Ephedra

Pollination in Ephedra (Gnetales)
Kristina Bolinder
Department of Ecology, Environment and Plant
Sciences
Stockholm University
Supervisor: Catarina Rydin
Bolinder, K. Licentiate thesis, 2014
Abstract
Pollination, i.e., the transport of male gametophytes to female gametophytes, can occur with
biotic or abiotic vectors and is necessary for fertilization and completion of the lifecycle in all
seed plants. Insect pollination and the co-evolution between angiosperms and insects have during
the last century been discussed as one possible solution to Darwin’s abominable mystery and an
important explanation for the relatively abrupt turn-over from a vegetation dominated by
gymnosperms to a vegetation dominated by angiosperms in the Cretaceous. Insect pollination is,
however, a much older phenomenon that can be traced back to the Devonian, but is it an ancestral
trait that has been lost in many seed plant groups, or has it originated multiple times in parallel?
These questions have to be addressed in a phylogenetic framework comprising extant and extinct
seed plant groups. The Gnetales are constantly in focus in studies of seed plant phylogeny,
probably because they have repeatedly been suggested, and refuted, to be the closest living
relatives of angiosperms. The order consists of three genera, Gnetum, Welwitschia and Ephedra,
of which the former two have long been known to be insect pollinated. Pollination biology in
Ephedra has, however, been poorly studied and understood. In this thesis pollination mechanisms
in Ephedra (Gnetales) are investigated by field experiments and observations (Paper I) and
aerodynamic simulations and studies of pollen morphology (Paper II). The results show that there
are multiple pollination mechanisms within this otherwise morphologically and ecologically
uniform genus. Further, in contrast to what has often been assumed, insect pollination is shown to
be ancestral in the Gnetales and not a derived feature that has evolved within the group. Using
this new information on pollination biology in the Gnetales and data from the literature, I explore
evolution of pollen morphology and pollination mode in seed plants.
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Bolinder, K. Licentiate thesis, 2014
List of Papers:
The following papers, referred to in the text by their roman numerals, are included in this thesis.
I
Bolinder, K., Humphreys, A.M.H., Ehrlén, J., Alexandersson, R., Ickert-Bond, S.M.,
& Rydin, C. Pollination mechanisms in the ancient gymnosperm clade Ephedra (Gnetales).
Manuscript.
II
Bolinder, K., Niklas, K.J. & Rydin, C. Aerodynamics and pollen ultrastructure in
Ephedra (Gnetales). Manuscript.
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Bolinder, K. Licentiate thesis, 2014
Contents
Abstract ............................................................................................................................................ 2
List of Papers:................................................................................................................................... 3
Pollination in the Gnetales and implications for the evolution of insect pollination in seed plants 5
Introduction .................................................................................................................................. 5
Material and methods ................................................................................................................... 6
Taxon sampling and character coding:..................................................................................... 6
Character evolution: ................................................................................................................. 6
Results and Discussion ................................................................................................................. 6
Paleozoic seed plants ................................................................................................................ 7
Mesozoic seed plants ................................................................................................................ 9
Ginkgo .................................................................................................................................... 11
Conifers .................................................................................................................................. 11
Gnetales .................................................................................................................................. 12
Cycadales ............................................................................................................................... 13
Angiosperms........................................................................................................................... 14
Conclusions ................................................................................................................................ 15
Pollen morphology in an evolutionary perspective ................................................................ 15
Evolution of insect pollination ............................................................................................... 16
Future perspective ...................................................................................................................... 17
Svensk sammanfattning (Swedish Summary) ............................................................................ 18
Acknowledgements, Tack! ......................................................................................................... 19
References .................................................................................................................................. 20
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Bolinder, K. Licentiate thesis, 2014
Pollination in the Gnetales and implications for the evolution of insect
pollination in seed plants
Introduction
Pollination involves the transportation of pollen (male gametophytes) to female gametophytes
that leads to fertilization and reproduction in seed plants. The transportation can occur by means
of abiotic vectors, for example wind or water, or by biotic vectors, for example insects or other
animals. The relationship, through which plants rely on pollinators for their reproduction and
pollinators rely on plants as a food source, was described already in 1793 by Sprengel and has
fascinated scientist ever since (Sprengel 1793). The adaptation to insect pollination has been
discussed as one of the explanations for the turn-over to an angiosperm dominated flora in the
Cretaceous (for details on the geological time scale, see Appendix 1) (Hickey and Doyle 1977,
Regal 1977, Crepet 1979, Burger 1981, Tiffney 1984, Bond 1989). However, insect pollination is
probably a much older phenomenon.
Investigations of the evolution of insect pollination need to be conducted in a phylogenetic
framework, which takes into consideration relationships among extinct and living seed plants.
Based on morphological data (Crane 1985, Doyle and Donoghue 1986, Loconte and Stevenson
1990, Doyle and Donoghue 1992, Doyle and Donoghue 1993) and molecular data (Chaw, et al.
2000, Rydin and Källersjö 2002) the Gnetales are strongly supported as monophyletic but their
relationship to the other five clades of seed plants has been very difficult to resolve (Chase, et al.
1993, Källersjö, et al. 1998, Chaw, et al. 2000, Rydin and Källersjö 2002, Schmidt and
Schneider-Poetsch 2002, Doyle 2008, Mathews 2009, Rydin and Korall 2009, Mathews, et al.
2010). Also, or maybe therefore, to be able to understand the evolution of insect pollination in
seed plants, the understanding of pollination mechanisms in the Gnetales is of great importance.
Pollination biology in the Gnetales has been studied for a few species, i.e., Gnetum gnemon,
Gnetum cuspidatum (Kato, et al. 1995), Welwitschia (Wetschnig and Depish 1999), and a few
species of Ephedra (see Paper I for references and details). Nevertheless, pollination biology in
the Gnetales is considered poorly investigated and understood (Endress 1996, Gorelick 2001).
Previous studies have, for example, come to deviating results on pollination in Ephedra. A trend
towards entomophily in the genus has been suggested (Bino, et al. 1984b), but field observations
of pollination in Ephedra has previously never been assessed in an evolutionary framework.
Together with collaborators, I have investigated pollination mechanisms in Ephedra, using
mechanistic field experimentation (Paper I), and aerodynamic simulations (Paper II). Here I put
the resulting conclusions on pollination biology in the Gnetales in the perspective of evolution of
insect pollination and pollen morphology in seed plants. When did insect pollination evolve? Is
the presence of pollen sacs correlated with wind pollination and is a saccate pollen diagnostic of a
clade of seed plants or has it evolved several times?
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Bolinder, K. Licentiate thesis, 2014
Material and methods
Taxon sampling and character coding: I selected a set of taxa that represent the major clades of
seed plants, and for which pollination biology is known or assessed for at least some taxa. I chose
four representative groups of extinct plants from the Paleozoic: Callistophytales, Cordaitales
Lyginopteridales and Medullosales; four groups of extinct plants from the Mesozoic:
Bennettitales, Caytoniales, Glossopteridales and Peltaspermales, and from the living clades:
angiosperms, cycads, Ginkgo, conifers (several conifer genera to investigate the evolution of
saccate pollen) and the Gnetales.
I have investigated pollen transfer in Ephedra (Gnetales) using field experiments; enclosing of
female branches in insect nets to deny insect access to the cones, pollen traps for investigation of
pollen dispersal, and diurnal and nocturnal insects observations (Paper I). Aerodynamic
properties of selected species of Ephedra were assessed using computer simulations and studies
of the ultrastructure of pollen grains of Ephedra (Paper II). Information on pollination mode and
pollen morphology in other major groups of extant and extinct seed plants was taken from the
literature.
Character evolution: Evolution of pollination was estimated using parsimony optimization of
two states: pollen transfer by biotic vector and pollen transfer by abiotic vector. Evolution of
saccate pollen was estimated using the same approach but as a multistate character: number of
pollen sacs 0, 1, 2 or 3. Ancestral character states were reconstructed, using accelerated
transformation optimization as described by Farris (1970) and delayed transformation
optimization (Swofford and Maddison 1987), on the most recent and most completely sampled
phylogeny of living and fossil seed plants (Hilton and Bateman 2006). Relationships in the
conifer crown group were modified according to most recent results (Leslie, et al. 2012). Further,
three different hypotheses regarding the phylogenetic position of the Gnetales were considered;
Gnetales member of an anthophyte clade (Crane 1985, Chase, et al. 1993), Gnetales sister to
conifers (Rydin, et al. 2002) and the Gnetales nested among conifers, sister to the Pinaceae
(Chaw, et al. 2000, Mathews, et al. 2010).
Results and Discussion
Seed plants can be traced back to the Devonian; the oldest known fossil remains are cupulated
and integumented ovules/seeds, e.g., Elkinsia from the late Devonian, or possibly Runcaria from
the middle Devonian (Taylor, et al. 2009). Many of the Paleozoic seed plants are referred to as
“seed ferns”, which is the loosely defined collective term for extinct seed plants with “fern-like”
leaves. Here, I avoid this term throughout. The male gametophyte of the earliest gymnosperms
shows similarities to both the microspores of heterosporous free-sporing plants with trilete or
monolete laesurae, and to true pollen of Mesozoic and Cenozoic seed plants. These grains are
called prepollen (Chaloner 1970), and are ancestral in seed plants and characteristic of Late
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Bolinder, K. Licentiate thesis, 2014
Paleozoic seed plants. They lacked a pollen tube and germinated proximally though the laesurae,
as do spores, but were multicellular as is pollen. Although, the insect fauna was diverse during
the Carboniferous, pollen morphology and ovule reception methods suggest that anemophily was
the dominant transfer mechanism during the Paleozoic. Also, the integument of early
gymnosperms may have evolved as a response to its aerodynamic effect on successful pollination
(Niklas 1981a, Niklas 1981b) but possibly both pollination and protection were important for the
adaptive evolution of an integument (Rothwell and Scheckler 1988).
Pollen is likely to be the first reward for insects offered by plants, e.g., prepollen of Lagenostoma
(Lyginoperidales) or the very large prepollen grains of Medullosans. If only pollen was the first
important nutritional reward, a bisporangiate condition would be necessary for successful
pollination in the early insect pollinated lineages. However, according to Crepet (1979) the
mandibulate mouthparts suitable for chewing pollen were also suitable for predation of ovules
and young seeds, and pollen and ovules were probably equally important reward sources to early
pollinators (Crepet 1979). This could thus explain why insects would be motivated to visit both
male and female organs that possibly were located on different plants (dioecious plants), or at
least on different cones (monoecious plants). Beetles were the most diverse and abundant order of
anthophilous insects during the time when insect pollination may have originated, and they were
probably the first insect-pollinators (Crepet 1979). Still today are beetles extensive pollenfeeders, and the pollinators of some angiosperms and cycads.
Paleozoic seed plants
Callistophytales
Callospermarion pusillum from the middle Pennsylvanian is the earliest documented fossil
evidence for a pollination drop mechanism (Rothwell 1977). The microgametophytes of
Callistophytales, monosaccate true pollen, about 40µm in diameter (Taylor 1979) with an
alveolate exine (Taylor and Zavada 1986) was surprisingly modern for a Paleozoic plant. These
grains germinated from the distal pole, and there is even some evidence for the presence of a
branched pollen tube (Taylor, et al. 2009). Ovules occurred on the lower surface of fernlike
leaves and were facing downwards in relation to gravity (Rothwell 1981, Doyle 2010). The
pollen probably floated upwards in the pollination drop and fertilized the ovule. This mechanism,
which is similar to that of some conifers, was thus present already in the Carboniferous (Leslie
2008). Pollen transfer in Callistophytales is poorly understood. The pollen grains most likely had
a low density and a low settling velocity, associated with an increased capability of wind
dispersal (comparable to the saccate pollen of extant Pinus (Schwendemann, et al. 2007). Thus,
there is some circumstantial evidence for wind pollination in the Callistophytales. Although the
presence of capitate glands on the ovulate structures may represent attractive structures analogous
to nectar bodies (Taylor 1979), most current evidence suggests that Callistophytales were
predominantly anemophilous plants.
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Bolinder, K. Licentiate thesis, 2014
Cordaitales
The cordaites were Palaeozoic trees that could be nearly 30 m high with a diameter of 1 m in at
the base of its trunks (Scott 1909), but could also be smaller trees with a height of 5 m and with
stilt roots (Cridland 1964). Cordaites were probably monoecious (Bell and Hemsley 2000), and
the compound fructifications consisted of a primary axis with monosporangiate cones in the axils
of the bracts (Biswas and Johri 1997). The cones had spirally arranged scales with pollen sacs or
ovules located close to the apex of elongated stalks (Florin 1951). The orientation of the ovules is
not known for certain, but the micropyle was probably facing away and outwards from the cone
axis at time of pollination (Scott 1909). The cordaites had true pollen with an alveolate pollen
wall (Taylor and Zavada 1986), distal germination (Bell and Hemsley 2000) and one pollen sac
(Florin 1951) of proportionately greater volumes than in extant conifers (Leslie 2008). The
integument of cordaites most likely played an active role in sealing the pollen chamber after
pollination had occurred (Rothwell 1988). The pollen morphology circumstantially supports the
cordaites as wind-pollinated.
Lyginopteridales
The Lyginopteridales are a diverse and perhaps paraphyletic assemblage of Paleozoic seed plants,
of which many are poorly documented and understood. Although many details are known from
vegetative and (female) reproductive organs, the structures have not always been found in
connection and possibilities for interpretation of whole plant concepts and the environmental
preferences of the plants are limited. Most members of the Lyginopteridales had narrow stems
and are thought to have had a scrambling or climbing habit (Masselter, et al. 2007, Taylor, et al.
2009). Pollen organs associated with the Lyginopteridales consist of clusters of fused or nonfused microsporangia. The prepollen was small with smooth surface and a trilete laesura. Pollen
transfer is uncertain. It may have occurred with insects as vectors; their ovules were born single
in tulip-shaped cupules, which had prominent glands on the abaxial sides of the cupule lobes
(Oliver and Scott 1904). However, these glands may also have functioned for defense against
predation, and the small and smooth prepollen may have been well-adapted for wind pollination.
In conclusion, it is difficult to assess the mode of pollen transfer in this poorly understood order,
and I have for this survey followed Taylor et al., (1988, 2009) who state that pollen of the
Lyginopteridales were wind-borne.
Medullosales
The Medullosales were similar to tree-ferns, with fern-like leaves, but employed a typical
gymnospermous mechanism of pollen capture using a pollination drop mechanism (Rothwell
1977). The monolete prepollen grains of Medullosa were extremely large, up to 0.6 mm, with a
very thick sporoderm (Taylor 1979) most likely associated with a high terminal settling velocity
and a reduced dispersal capability. Medullosans are found in coal swaps where they probably
grew as a part of the understory vegetation (Wnuk and Pfefferkorn 1984). The reduced wind
speed in understory vegetation (Whitehead 1983) in combination with the large, dense
morphology of their prepollen makes wind pollination highly unfavorable (Taylor 1979). Further,
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Bolinder, K. Licentiate thesis, 2014
Medullosans are found scattered e.g., among the more dominant tree-like Marattialean fern
Psaronius in floodplains (DiMichele and Phillips 1988). Wind-pollinated taxa typically grow in
large monotypic stands and are rarely scattered within stands of other species (Whitehead 1983),
as Medullosans appear to have been. Thus, circumstantial evidence clearly supports Medullosans
as among the earliest known enthomophilous plants, most likely pollinated by pollen-feeding
insects (Crepet 1979).
Mesozoic seed plants
Bennettitales
The Bennetittales are a group of extinct seed plants that were abundant and diverse during the
Triassic, Jurassic and Cretaceous (Harris 1969, Watson and Sincock 1992). The reproductive
organs of at least some bennettitalean taxa are somewhat similar to the angiosperm flower and
morphologically diverse; both unisexual and bisexual structures have been described (Friis, et al.
2011). In the bennettitalean microsporangiate structure Weltrichia from the Jurassic, pollen sacs
are placed inside bivalvate synangia (Harris 1969). The unisexual flower consists of a whorl of
bracts that maybe free or fused to a cup that protected the developing pollen sacs, or functioned
as attraction for insect visitors (Friis, et al. 2011). The internal surface of the bracts in Weltrichia
sol is covered with small sacs that contain resinous bodies and are tentatively interpreted a
remains of nectaries (Harris 1969). Pollen of the Bennettitales is relatively large, ovoid and
psilate, with a longitudinally oriented sulcus (Osborn and Taylor 1995) and share a granular
architecture of the infratectum with those of the Erdtmanithecales, Gnetales and Pentoxylales
(Osborn 2000). Pollen of Cycadeoidea dacotensis (Lower Cretaceous), found in situ, show a
dense granular infratectum that is unlikely to be an artifact resulting from the fossilization
process (Osborn and Taylor 1995). Consequently, this pollen probably had a high settling
velocity and a poor flight capability, as is here demonstrated for the gnetalean Ephedra foeminea
and inferred for Welwitschia (Paper II). Ovulate structures of the Bennettitales vary from large
open and exposed radially symmetrical structures (Williamsoniella), to moderately sized
structures with enclosed microsporophyll (Cycadeoidea) (Harris 1969, Crepet and Friis 1987,
Friis, et al. 2011). The overall robust morphology of the bennettitalean reproductive structures,
and the large pollen grains, suggest that most species of the known taxa were pollinated by
beetles and possibly had a pollination syndrome similar to that of extant Magnolia (Crepet and
Friis 1987, Friis, et al. 2011).
Caytoniales
Caytonia was first discovered by Thomas (1925). Based on the morphological similarities with
several groups of so called “seed ferns”, and with angiosperms, he treated them as “intermediate”
between gymnosperms and angiosperms (Thomas 1925). Also in some more recent phylogenetic
studies based on both molecular and morphological data, Caytonia is sister to the angiosperms
(Doyle 1996, Doyle 2008). The female reproductive structure of Caytonia consists of ovules,
most likely with the micropylar opening facing downwards in relation to gravity. The ovules
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Bolinder, K. Licentiate thesis, 2014
were borne several together and surrounded by an enclosing cupule, with an opening at the end
(Harris 1964). The number of ovules in each cupule varies, in C. sewardi there are up to ten
ovules and in C. thomasi there are up to 30 ovules in each cupule (Harris 1933). The pollen
grains were bisaccate (Harris 1964, Doyle 2010) and have been found in situ in the micropyle of
the ovule (Harris 1951), which thus rejects ideas of angiospermy in Caytonia. The pollen sacs
had a completely different ultrastructure than those of extant conifers (Osborn 2000), but
functioned as a floating device for entering inverted ovules in a similar way as occurs in some
extant conifers (Leslie 2008). The sacs are in addition likely to function as an aid for air dispersal,
as do the sacs of pollen of the Pinaceae and the Podocarpaceae. The pollination syndrome and
fertilization mechanism in Caytonia were probably similar to those of extant conifers (Harris
1933, Harris 1964) and Caytonia was thus most likely wind-pollinated.
Glossopteridales
Glossopterids were a highly successful group of gymnosperms that dominated the vegetation of
many Late Carboniferous ecosystems. The diversity of Glossopterids started to decline in the
Triassic and they went entirely extinct during the Jurassic (Stewart and Rothwell 1993). The
ovulate organs consisted of a stalked fertile head often attached to a modified leaf-like organ
(Gould and Delevoryas 1977). There is considerable variation in morphology and mode of
attachment to the leaf-like structure and it is not clear whether or not the Glossopterids are a
monophyletic group (Biswas and Johri 1997). There is a wide range of variation in number of
heads attached to the leaf-like organ as well as number of ovules in each head. In Scutum there
are up to 75 scattered ovules while in Denkania there is only one ovule in a cupule-like head
(Surange and Chandra 1975). The pollen grains of Glossopterids are bisaccate with characteristic
transverse striations on the corpus (Gould and Delevoryas 1977) and were, like most conifers,
most likely wind-pollinated.
Peltaspermales
Peltasperms were widespread on the Gondwana and the northern continents from the
Pennsylvainian to the Triassic (Taylor, et al. 2009). They are associated with fern-like fronds
referred to several form-genera, of which Lepidopteris is sometimes used for entire plants based
on similarities in e.g., stoma structures (Stewart and Rothwell 1993). Reproductive morphology
was probably diverse; ovules and microsporangia may be attached to fertile (parts of) fronds or to
fan-shaped or peltate sporophylls (Taylor, et al. 2009). The early Permian peltasperm Autunia
had bisaccate pollen (Vesicaspora) (Kerp 1988, Doyle 2010) and open seed-bearing structures
(Kerp 1988, Naugolnykh and Kerp 1996) with one or two ovules attached to a fan shaped
megasporophyll downwards oriented in relation to gravity (Kerp 1988). Autunia were most likely
wind pollinated and is coded as such here. The late Permian peltasperm Vittatina lack pollen sacs
on the pollen grains (Hart 1966, Meyen 1984). Furthermore, pollen grains of Vittatina have been
found in the gut of the Permian insect Idelopsocus (Krassilov and Rasnitsyn 1996)
circumstantially supporting Vittatina as insect pollinated.
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Bolinder, K. Licentiate thesis, 2014
Ginkgo
The earliest known ginkgoalean fossil is the Trichopitys, from the Early Permian, and the group
was abundant in the northern hemisphere during the Mesozoic and early Cenozoic (Bell and
Hemsley 2000). The only living species of this genus is Ginkgo biloba endemic to China. It is
dioecious with male and female individuals occurring at a 1:1 ratio (Santamour Jr, et al. 1983).
The pollen grains are non-saccate and boat-shaped with a large longitudinal aperture extending
over the entire grain (Wodehouse 1935). They can be dispersed extremely long distances. In the
Boston area, the more than 400 m distance between the closest male and female tree does not
inhibit seed set (Del Tredici 1989). Thus, Ginkgo biloba is clearly wind-pollinated (Del Tredici
2007). The ovules are usually borne in pairs, symmetrically attached at the end of a stalk-like
sporangiophore and facing upwards in relation to gravity (Bell and Hemsley 2000). At the time of
pollination the small pollination droplet captures the air borne pollen (Jin, et al. 2012a). When
conspecific pollen is captured, the secretion terminates and the pollen enters the pollen chamber
as a result of evaporation and active withdrawal (Jin, et al. 2012b). The pollen grain germinates
into a tube with haustorial function, which releases motile spermatozoids into the fluid located
above the archegonia (Friedman 1987). This example of zooidogamous fertilization was
discovered already in 1896 by Hirase (Hirase 1896).
Conifers
The oldest known conifers had saccate pollen grains (Florin 1951). Among extant conifers,
saccate pollen is restricted to some members of the Podocarpaceae and the Pinaceae (Doyle 1945,
Tomlinson 1994, Salter, et al. 2002, Leslie 2010). The number of pollen sacs varies from one sac
in Tsuga (Pinaceae) to three pollen sacs in Microstrobus and Dacrydocarpus (Podocarpaceae)
(Appendix 2) (Hesse, et al. 2008). The absence of pollen sacs in pteridophytes with winddispersed spores suggest that the primary function of the sacs is as a floating device for the pollen
grain and or aid to float up the pollination drop and fertilize the ovule (Doyle 1945, Tomlinson
1994, Runions and Owens 1996, Leslie 2008). And extant conifers with saccate pollen also show
erect stobili with ovules facing downwards in relation to gravity, and a pollination drop produced
by the plant or by rainwater (Doyle 1945, Tomlinson 1994, Runions and Owens 1996, Salter, et
al. 2002, Leslie 2010). However, pollen sacs is in addition interpreted as aid for pollen dispersal
by decreasing the density and settling velocity of the pollen grain, and thus increase its dispersal
capability (Proctor, et al. 1996, Schwendemann, et al. 2007). The Araucariaceae, Saxegothaea
(Podocarpaceae), and some Pinaceae (Abies and Tsuga) have no pollination drop-mechanism
(Eckenwalder 2009), and also (mostly) nonsaccate pollen (Eckenwalder 2009). In few other taxa,
Larix and Pseudotsuga (Pinaceae), drop production is delayed until after pollen has landed on the
dry micropylar surfaces (Gelbart and von Aderkas 2002). Also these two genera have nonsaccate
pollen (Eckenwalder 2009). All extant conifers, even those without pollen sascs on the pollen
grains, disperse their pollen grains by wind (Owens, et al. 1998). Wind pollination is also
assumed for the extinct crown group conifer clade the Cheirolepidiaceae, based e.g., on the
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Bolinder, K. Licentiate thesis, 2014
widespread occurrence of their characteristic pollen (Classopollis) (Taylor 1988). Classopollis
displays columellate exines and a circumpolliod colpal-like feature (Traverse 1988).
Gnetales
The Gnetales consist of three distinct monophyletic genera, Ephedra L., Gnetum L. and
Welwitschia Hook.f. Ephedra comprises about 40 xerophytic species in Eurasia and the
Americas. Gnetum is restricted to tropical rain forests and consists of about 30 species.
Welwitschia includes only one species endemic to the Namib Desert.
Ephedra
Ephedra has in general been referred to as wind-pollinated (Kubitzki 1990) and empirical studies
have come to different conclusions. Jaccard (1894) proposed wind-pollination for E. helvetica
based on field observations, confirmed by field experiments (Paper I), the pollen ultrastructure
(Paper II) and the absence of pollination drop producing structures in the male cone.
Aerodynamic experiments on the two North American species E. trifurca and E. nevadensis
show that their cone and pollen morphology is compatible with wind pollination (Niklas, et al.
1986, Niklas and Kerchner 1986, Niklas and Buchmann 1987, Buchmann, et al. 1989). In
contrast, E. aphylla has been described as partly entomophilous (Bino, et al. 1984a) and E.
foeminea has been suggested to be exclusively entomophilous or entomophilous in combination
with anemophily (Porsch 1910, Meeuse, et al. 1990). Bino, et al. (1984a) suggest an evolutionary
trend towards entomophily within the genus. However, in Paper I, we conclude that the case is
actually the opposite. Entomophily is ancestral in Ephedra, and in the Gnetales, and shift towards
anemophily is possibly associated with the re-radiation of the genus (Paper I) 30 million year ago
(Ickert-Bond, et al. 2009). The derived adaptations to anemophily extend to the
microgametophytic level and pollen grains of wind-pollinated taxa have lower settling velocity
associated with a more spacious exine (Paper II). Even though dispersal aid is suggested to be a
secondary function the sacs of pollen of some conifers, it is nevertheless interesting to think
about the functional similarities in pollen dispersal between the spacious infratectum in plicae in
wind-pollinated Ephedra (Paper II), and the pollen sacs of members of the Pinaceae,
Podocarpaceae and many Paleozoic seed ferns (see above).
Gnetum
Most species of Gnetum have morphological bisexual, functionally unisexual, male reproductive
structures, in which also male plants can produce sugary pollination drops and are emitting a
strong scent (Endress 1996). Accordingly, entomophilous pollination syndrome is suggested for
the genus by van der Pijl (1953), and Kato (1994, 1995). Gnetum gnemon is shown to be
pollinated by nocturnal moths of Pyralidae and Geometridae whereas G. cuspidatum is pollinated
by small flies of Lauxaniidae (Diptera) (Kato, et al. 1995). In both species, pollinators are
attracted by strong scent (Kato and Inoue 1994, Kato, et al. 1995). Pollen grains of Gnetum is
spheroidal, inaperturate, and Gnetum is the only gymnosperm with spinose to spinulose
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Bolinder, K. Licentiate thesis, 2014
ornamentation, although the surface sculpture varies among species (Gillespie and Nowicke
1994). The spinulose ornaments of Gnetum are homologous with the plica of Ephedra and
Welwitschia (Osborn 2000, Yao, et al. 2004), and their ultrastructure is similar. The exine in
Gnetum pollen has a dense granular infratectum in the spinolose regions and a thin tectum
uniform throughout the grain (Yao, et al. 2004, Tekleva and Krassilov 2009). A spinulose
ornamentation is common among entomophilous taxa, and maximizes the number of pollen
grains that attach to the pollen vector (Wodehouse 1935, Faegri and van der Pijl 1979, Ackerman
2000, Culley, et al. 2002). In addition, pollen grains of Gnetum are sticky, even though they lack
pollen kitt (Hesse 1980, Hesse 1984), and adhere to the proboscides antennae of visiting moths or
to the antennae and body of visiting flies (Kato, et al. 1995).
Welwitschia
Both male and female reproductive organs of Welwitschia mirabilis produce sugary pollination
drops (Endress 1996) that are since long known to attract insects (Hooker 1863, Baines 1864,
Pearson 1906). The species was through field experiments and field observations shown to be
insect-pollinated, mainly by diurnal dipterans (Pearson 1909, Wetschnig and Depish 1999).
However, as far as known, no nocturnal observations have been conducted on Welwitschia and
since both Gnetum (Kato, et al. 1995) and Ephedra foeminea (Paper I) is pollinated by nocturnal
moths it would be very interesting to see if there are any nocturnal visitors/pollinators of
Welwitschia mirabilis. Pollen grains of Welwitschia are polyplicate and similar to those of
Ephedra, but are monoaperturate; a broad sulcus extends over the entire grain (Wodehouse
1935). The pollen grains lack pollen kitt but become sticky from tapetal debris (Hesse 1984) and
are so adhesive that our attempts to investigate their terminal settling velocity failed (Paper II).
However, previous authors state that the pollen grains of Welwitschia can travel only short
distances (Wetschnig and Depish 1999), and a dense architecture of their exine has been observed
(Paper II). These observations are consistent with a high settling velocity (i.e. similar to the case
of Ephedra foeminea) (Paper II), which thus supports previous conclusions on entomophily in
this monotypic genus.
Cycadales
The Cycadales are an ancient group that shares many presumably ancestral features with extinct
Paleozoic seed plants, for example a zooidogamous fertilization mechanism (also present in
Ginkgo), discovered already in 1896 (Ikeno 1896). The Cycadales appear for the first time in the
fossil record during the Triassic (Crane 1986), and their diversity maximum was during the
Jurassic-Cretaceous (Jones and Stevenson 1993, Watson and Cusack 2005). Extant clades (about
300 species in 11 genera,Hill, et al. 2004), are however thought to have radiated simultaneously,
and as recent as the late Miocene (Nagalingum, et al. 2011). Aerodynamic experiments suggests
that wind pollination alone may not be that efficient in cycads (Niklas and Norstog 1984), and
Chamberlain (1935) observed a decrease in seed set with an increased distance from nearest
microsporangiate plant. In most species of cycads, the ovules are enclosed by cone bracts at time
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Bolinder, K. Licentiate thesis, 2014
of pollination (Jones and Stevenson 1993). This obstructs pollen access to the ovules, and
pollination requires two phases: first the transportation of pollen grains to the female
megastrobilus and, in most cases, a second transportation from the megasporphylls to the ovules
(Niklas and Norstog 1984). Cycad pollen is monosulcate and bilaterally symmetrical
(Wodehouse 1935, Dehgan and Dehgan 1988). The exine is generally alveolate (Taylor and
Zavada 1986) but the structure of the alveoli varies between the genera (Dehgan and Dehgan
1988) and so does the pollination syndrome.
Cycas
The megastrobili of Cycas deflect airflow passing over the cone toward leeward where pollen
grain accumulates (Niklas and Norstog 1984). The loose aggregation of the sporophylls makes
the ovules directly accessible to air-borne pollen, although some passive secondary transport of
pollen by water is most likely required for successful fertilization (Niklas and Norstog 1984).
Wind-pollinated plants generally produce dry, light, pollen in large amounts (Faegri and van der
Pijl 1979). Pollen grains of Cycas are subcircular in shape with a fossulate surface (Dehgan and
Dehgan 1988) and are to a certain degree adapted to wind pollination (Faegri and van der Pijl
1979). The comparatively big male cones of C. circinalis shed large amounts of pollen at time of
pollination (Norstog 1987), which further supports Cycas as wind-pollinated.
Zamia
In contrast to Cycas, Zamia is most likely exclusively or partly insect-pollinated (Niklas and
Norstog 1984, Norstog, et al. 1986, Tang 1987). Pollen of extant (Dehgan and Dehgan 1988) and
fossil (Hill 1990) Zamia is broadly elliptic in shape and the alveolate exine is multilayered and
similar throughout the genus (Dehgan and Dehgan 1988). Male cones of Zamia are
comparatively small and produce far less amounts of pollen than do male cones of Cycas
(Norstog 1987). Some pollen-transportation to the megastrobili occurs initially by wind and
becomes secondarily transported to the ovules by insects (Niklas and Norstog 1984). In Zamia
furfuraceae (Norstog, et al. 1986) and Z. pumila (Tang 1987), successful pollination may,
however, occur in the absence of anemophilous pollen, by means of different species of the
weevil Rhopalotria. Larvae of the weevil feed on tissue of the microsporangiate cone, pupate at
inside the microsporangiate cone, and hatch as pollen-coated adults. Mature weevils visit the
ovulate cones but are non-destructive to ovules, and thus effective pollinate the plant (Norstog, et
al. 1986, Tang 1987).
Angiosperms
Numerous studies with the attempt to determine the age of the angiosperm crown group has been
conducted during the last century (Ramshaw, et al. 1972, Magallón and Sanderson 2001,
Wikström, et al. 2001, Bell, et al. 2010, Magallón 2010). Wikström et al. (2001) and Bell et
al.(2010) estimate its age to the Early to Middle Jurassic, and Magallón (2010) to the Triassic.
The earliest recognized angiosperm remains are younger, however, and consists of scattered
14
Bolinder, K. Licentiate thesis, 2014
pollen. Synapomorpic for all angiosperm pollen is the columellate-reticulate architecture of the
exine (Doyle 1978), and indisputable angiosperm pollen grains are known from the earliest
Cretaceous (Valanginian-Hauterivian) (Friis, et al. 2011). Pollen grains that share some but not
all their features with angiosperm pollen are reported from the Middle Triassic (Hochuli and
Feist-Burkhardt 2013), and these grains were conceivably produced by extinct plants that
represent stem groups along the lineage to the angiosperm crown group. The earliest angiosperms
are repeatedly considered to have been insect-pollinated (Bernhardt and Thien 1987, Crepet and
Friis 1987, Gottsberger 1988, Hu, et al. 2008) and possibly pollinated e.g., by beetles, flies
(Empididae), micropterigid moths, sawflies and sphecid wasps. All these insect groups are
known from the Early Cretaceous (Crepet and Friis 1987), and co-evolution with pollinators and
a pollinator driven speciation are thought to be one of the mechanisms of angiosperm
diversification in the Cretaceous (Hickey and Doyle 1977, Regal 1977, Crepet 1979, Burger
1981, Tiffney 1984, Bond 1989). A consequence of this hypothesis is that wind pollination is a
derived state in angiosperms, thought to have evolved repeatedly in response to ecological
conditions that make animal pollination less favorable (Linder 2000, Friedman and Barrett 2008).
However, based on my brief survey I find it clear that pollination biology and pollen morphology
varies considerably among and within early diverging angiosperm clades, even to the extent that
it was difficult or impossible to score the ancestral states of angiosperms in my data matrix (see
further below).
Conclusions
Pollen morphology in an evolutionary perspective
Evolution of three different pollen traits (Appendix 2) was assessed under three topological
frameworks that differ (only) regarding the position of the Gnetales: sister to Pinaceae (Figs 1ac), sister to conifers (not shown) and sister to angiosperms and allied extinct taxa (not shown).
Regardless of the relationship of the Gnetales to other seed plant groups a rounded shape of
pollen grains is the ancestral state in conifers and in the anthophyte clade (equivocal in
anthophytes if Gnetales are included in anthophytes) (Fig. 1a). Transitions to boat-shaped pollen
have occurred repeatedly, for example within the Gnetales and Bennettitales. Among earlier
diverging clades accelerated and delayed transformations to boat-shaped pollen produce, under
my topological framework, equally parsimonious results. Aperture (regardless of direction or
shape) evolved early in the history of seed plants (Fig. 1b), but is however missing in several
clades within the Gnetales. Repeated losses of the aperture within the Gnetales (Ephedra and
Gnetum), or one loss and regains in Welwitschia, are equally parsimonious (Fig. 1b).
Many Paleozoic groups with true pollen had one or several pollen sacs (Millay and Taylor 1974),
a feature that typically is correlated with downward oriented ovules (Leslie 2008, Hernandez‐
Castillo, et al. 2009). The flotation hypothesis, described by Doyle (1945) and Tomlinson (1994),
and experimentally tested by Leslie (2010), according to which pollen sacs mainly functions as a
15
Bolinder, K. Licentiate thesis, 2014
flotation device and pollen grains float upwards into the ovule, is well-known and widely
accepted for conifers. The same mechanism was however most likely established also among
other seed plants, such as Callistophytes, Caytonia and Glossopterids, and was thus present
already during the Paleozoic (Leslie 2008, Doyle 2010, Leslie 2010). Callistophytes are
sometimes discussed as possibly related to conifers and cordaites, but the presence of pollen sacs
(and perhaps an associated floatation function) in pollen of Glossopterids and Caytonia appears
to be independently evolved. In extant plants saccate pollen is restricted to some genera of the
Pinaceae and Podocarpaceae. Monosaccate pollen present in Tsuga (Pinaceae) but in general rare
among living plants (Appendix 2). From my survey it is not possible to assess whether saccate
pollen is ancestral within conifers, or has originated several times, and twice within extant
conifers (Fig. 1c). Evolution of trisaccate pollen in the Podocarpaceae is also unclear (Fig. 1c).
Character evolution of pollen sacs shows a comparatively complicated pattern, which would be
interesting to model across a sample of trees. Regarding pollination, I conduct these analyses
using a relatively small set of terminals, and optimizing a single binary state character, for which
I suggest multiple transformations along branches are unlikely. In such cases, parsimony has
been shown to be more appropriate for ancestral state reconstruction than methods that employ
more parameter rich models (Pirie, et al. 2012). A major drawback of my approach is however
that I optimize the character on only three alternative topologies, the reliability of which can be
questioned. In that respect, optimization over a sample of Bayesian trees could have been
advantageous. The relationship among major clades of seed plants is a very difficult phylogenetic
question, far beyond the scope of this study. In my opinion, it is nevertheless interesting to
investigate the evolution of pollination biology and pollen morphology, using the currently best
estimate of phylogeny of seed plant as a framework.
Evolution of insect pollination
Mutualistic relationships between insects and plants in the form of pollination were established
well before the origin of the angiosperms, and co-evolution between angiosperms and insects
cannot solely explain the turn-over from a gymnosperm dominated to an angiosperm dominated
vegetation (Crepet and Niklas 2009). There are several early examples of entomophilous seed
plants, for example the Carboniferous Medullosans and Mesozoic groups such as some
Peltasperms and the Bennettitales. My character optimization unequivocally resolves insect
pollination as independently evolved in Medullosans, Peltasperms and cycads (Figs 2a-c). This is
consistent with indications based on literature information on these respective clades. For
example, circumstantial evidence (most importantly a transition from open seed-bearing
structures to ovules enclosed in cupules, and a transition from saccate to non-saccate pollen)
supports a shift to insect pollination within Peltasperms (Meyen 1984) (see also above).
Similarly, although insect pollination has been suggested for many extant cycads, the alveolate
pollen exine of extant (Dehgan and Dehgan 1988) and fossil (Hill 1990) species is most likely
associated with a low settling velocity. This indicates, in accordance with my optimization, that
anemophily is the ancestral pollination syndrome in the Cycadales.
16
Bolinder, K. Licentiate thesis, 2014
It is, however, unclear from my optimization whether or not insect pollination evolved
independently in the Gnetales, the Bennettitales and the angiosperms (Figs 2a-c). As before, this
is true under all three topological frameworks used here, i.e., the Gnetales nested within the
conifer (Fig. 2a), sister to the Pinaceae (Fig. 2b), or members of an anthophyte clade (Fig. 2c)
(although an association between conifers and the Gnetales clearly means an independent origin
of insect pollination in the Gnetales). Furthermore, it appears questionable if insect pollination
should be considered ancestral in angiosperms, and I scored several characters as question marks
for angiosperms (Table 1). Recent character optimization by Hu, et al. (2008) resolves insect
pollination as ancestral in angiosperms, in line with ideas in many previous studies (references
above). However, this interpretation may be an oversimplification. My literature survey clearly
shows that many of the early diverging angiosperm clades, for example Amborella, Nymphaeales
and Trimeniaceae, are diverse in terms of pollen morphology (Endress and Honegger 1980,
Sampson and Endress 1984, Osborn, et al. 1991, Sampson 1993, Hesse 2001, Remizowa, et al.
2008), and probably also in pollination mode. Conceivably, early angiosperms were generalists
regarding pollination, utilizing several mechanisms simultaneously, and with morphological and
functional variation even within species and individuals.
Studies of the evolution of pollination require knowledge of pollination mode in extinct seed
plants, but such information related to function is not always readily available for fossils. Indirect
inference can sometimes be made, based for example on pollen morphology, ultrastructure of
pollen, the abundance of a certain pollen type as dispersed grains, and discoveries of structures
for pollinator reward. It is also possible to simulate aerodynamic properties of pollen grains and
female structures, and thereby assess how far pollen can travel by air and how efficiently ovules
can trap air-borne pollen. For the Gnetales, all available information points towards insect
pollination as the ancestral and prevailing state. My studies indicate that wind pollination evolved
relatively late in the evolutionary history of the Gnetales, i.e., in the current core Ephedra clade,
which is estimated to have originated only about 30 million years ago. In contrast to these
conclusions is the presence of a relatively abundant and widespread fossil record of dispersed
“ephedroid” pollen in the Cretaceous as well as in the Cenozoic, which as such may indicate
wind pollination.
Future perspective
I will continue my ongoing studies of morphology and ultrastructure of living and fossil
“ephedroid” pollen. The aim is that the results will prove useful for 1) evaluations of the
gnetalean affinity of different palynomorphs, 2) to infer the pollination biology of the plants that
produced the pollen, and 3) to assess the paleoenvironment, in which they lived in order to assess
the relevance of “ephedroids” as climatic indicators.
17
Bolinder, K. Licentiate thesis, 2014
Svensk sammanfattning (Swedish Summary)
Pollination, det vill säga transport av pollen från pollenproducerande organ till fröämnen,
förekommer med biotiska eller abiotiska vektorer och är i princip nödvändigt för befruktning och
fullbordandet av livscykeln hos alla fröväxter. Ett ömsesidigt förhållande mellan insekter och
växter där båda är beroende av varandra, insekter för föda och växter för dess förökning, har varit
känt ända sedan 1700-talet. Denna samevolution mellan insekter och växter har också diskuterats
som en möjlig förklaring till den, med geologiska mått, plötsliga övergången från en
gymnospermdominerad vegetation till en blomväxtdominerad vegetation under slutet av kritaperioden. Insektspollination är dock ett mycket äldre fenomen som går tillbaka ända till devonperioden, men är det en ursprunglig karaktär som sedan försvunnit i många fröväxtgrupper, eller
har insektspollination uppkommit parallellt hos avlägset besläktade grupper?
Dessa frågor måste undersökas i ett fylogenetiskt ramverk där både nulevande och utdöda
fröväxtgrupper finns med. Gnetales står ofta i fokus i studier som behandlar släktskap mellan
fröväxtgrupper och har upprepade gånger föreslagits, och motbevisats, som närmaste släktingar
till blomväxterna. Gnetales består av tre släkten, Gnetum, Welwitschia och Ephedra, varav de två
förstnämnda tidigare beskrivits som insektspollinerade. Få studier om pollinationsbiologin hos
Ephedra har publicerats och också med motsägande slutsatser.
I den här avhandlingen presenteras resultat av studier av pollinationsmekanismer inom Ephedra
(Gnetales) genomförda som fältexperiment och observationer (kapitel I) och genom
aerodynamiska simuleringar och studier av pollenmorfologin (kapitel II). Resultaten visar att det
finns flera pollinationssätt inom detta annars morfologiskt och ekologiskt homogena släkte.
Vidare, i motsats till vad som ofta antagits, är insektspollination ursprungligt inom släktet och
inom hela Gnetales, och inte en egenskap som utvecklats inom gruppen. Med hjälp av denna nya
kunskap om Gnetales pollinationsbiologi och litteraturuppgifter diskuteras här evolution av
pollenmorfologi och pollinationssyndrom inom fröväxter mer generellt.
18
Bolinder, K. Licentiate thesis, 2014
Acknowledgements, Tack!
Först och främst vill jag tacka min alltid lika engagerade handledare Catarina Rydin, för all
fantastisk handledning och allt fantastiskt stöd. Jag kan inte tacka dig nog!
Tack till Johan Ehrlén för perfekt statistikhandledning och pepp.
I would like to show my gratitude to Stefanie Ickert-Bond and Carina Hoorn. Steffi for all your
enthusiasm, sharing your knowledge of Ephedra and making science so much fun! Carina for
training me in palynology and for sharing fossil material and knowledge.
Thanks to Aelys Humphreys; always with an encouraging word and an answer to why my Rscript doesn’t work or how they can be improved. I really can’t thank you enough!
Karl Niklas thank you for having me as a guest in your lab at Cornell University and for the great
supervision and support in the preparation of Paper II.
Birgitta Bremer, för hjälpsamma kommentarer som förbättrat båda manuskripten och kappan,
Tack!
Kjell Jansson på Institutionen för Material och Miljökemi; alltid med en ny idé för att få till den
perfekta bilden, Tack!
Susanne Lindwall för allt stöd i morflabbet, Tack!
Thanks to all members of the former department of Systematic Botany for all fruitful discussions,
scientific and other… Additional thanks to all PhD students and master students that made the
work behind this thesis a blast: Annika, Åsa, Chen, Clara, Eva, Frida, Julia, Lena, Lina and Olle,
tack! Chen for being the best roomie, Annika, Åsa och Frida för att ni fått mig att inse tjusingen
och meditationskraften i stickning, Lena för att du delar min passion för pollen.
Avslutningsvis vill jag tacka Mamma, Pappa och Markus, för era insattser som fältassistenter i
Papper I, för ert omåttliga stöd och för att ni aldrig tröttnar på att höra om pollen, Ephedra och
allt annat som hör den här avhandlingen och fortsättningen till. Tack!
19
Bolinder, K. Licentiate thesis, 2014
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25
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Figure 1: Character evolution of three pollen traits, mapped onto a phylogeny of extant and extinct seed plants estimated by
Hilton and Bateman (2006) but with relationships among conifers constrained according to most recent results (Leslie et al.
2012) and the Gnetales constrained as sister to the Pinaceae. Ancestral state reconstruction was in addition performed on a
topology in which the Gnetales are sister to a) all conifers, and b) to angiosperms and allied extinct taxa (not shown, see text
for details). (a) Pollen shape. Rounded pollen grains is the ancestral state in conifers and the anthophyte clade (equivocal in
anthophytes if the Gnetales are included in anthophytes). Transitions to boat-shaped pollen grains have occurred within
several clades, e.g., the Gnetales and the Bennetittales. (b) Presence or absence of aperture (regardless of its shape and
direction). An aperture evolved early in the history of seed plants but is missing in several clades among the Gnetales.
Repeated losses, or one loss and regain in Welwitschia, are equally parsimonious. (c) Number of pollen sacci. In extant plants
saccate pollen is restricted to some genera of the Pinaceae and Podocarpaceae. Evolution of trisaccate pollen in the Podocarpaceae is unclear.
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wind
insect
Figure 2: Character evolution of pollination syndrome in seed plants. According to the results, insect
pollination has evolved independently in Medullosans, Peltasperms and cycads. From this survey it is not
clear whether insect pollination has evolved independently in the Gnetales, the Bennettitales and the
angiosperms, although an association between conifers and the Gnetales clearly means independent
evolution of insect pollination in the Gnetales. (a) Pollination syndrome optimized on a phylogeny, in
which the Gnetales are sister to conifers (b) sister to the Pinaceae, and (c) members of an anthophyte
clade.
Appendix 1
Geological time scale. Redrawn from Gradstein et al. 2012
CENOZOIC
Epoch
Epoch
Age
(Ma) Period
Holocene
Lopingian
70
Late
80
275
Guadalupian
Pennsylvanian
100
Miocene
110
120
20
325
Early
350
130
25
140
150
Late
160
400
170
40
Eocene
220
230
65
Paleocene
240
250
SILURIAN
Early
190
450
ORDOVICIAN
475
210
55
60
425
200
50
Middle
Early
Middle
Late
TRIASSIC
PALEOGENE
45
180
JURASSIC
35
Mississippian
Late
DEVONIAN
375
Oligocene
30
Cisuralian
300
CRETACEOUS
15
NEOGENE
90
10
Epoch
PERMIAN
Pleistocene
Pliocene
5
Age
(Ma) Period
PALEOZOIC
CARBONIFEROUS
Quat.
Age
(Ma) Period
MESOZOIC
500
CAMBRIAN
Middle
Early
525
Appendix 2
Group
Pollination
Prepollen/
pollen
pre-pollen
pre-pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
pollen
Aperture
Saccus/sacci
Lyginopteridales
wind
No, proximal germination; laesura(e) 0
Medullosales
insekt
No, proximal germination; laesura(e) 0
Bennettitales
insect
Yes, sulcus
0
Caytonia (Caytoniales)
wind
Yes?
2
Glossopteridales
wind
Yes?
2
Autunia (Peltaspermales)
wind
Yes?
2
Vittatina (Peltaspermales)
insect
No, inaperturate
0
Ginkgo (Ginkgoales)
wind
Yes, sulcus
0
Cordaitales
wind
Yes, distal pole
1
Callistophytales
wind
Yes, distal pole
1
Cheirolepidiaceae
wind
Yes, distal circle
0
Araucariaceae
wind
Yes, indistinct
0
Cupressaceae s.l.1
wind
Yes, distal circle
0
Tsuga (Pinaceae)
wind
Yes, indistinct
1
Pinus and Picea (Pinaceae)
wind
Yes, indistinct between sacci
2
Larix (Pinaceae)
wind
Yes, indistinct?
0
Pseudotsuga (Pinaceae)
wind
Yes, indistinct
0
Abies (Pinaceae)
wind
Yes, indistinct between sacci
2
Cedrus (Pinaceae)
wind
Yes, indistinct between sacci
2
Phyllocladaceae
wind
Yes, indistinct (between sacci?)
2
Podocarpus (Podocarpaceae)
wind
Yes, indistinct (between sacci?)
2
Microstrobus (Podocarpaceae)
wind
Yes, indistinct (between sacci?)
3
Dacrydocarpus
wind
Yes, indistinct (between sacci?)
3
(Podocarpaceae)
Dacrydium (Podocarpaceae)
wind
pollen
Yes, indistinct (between sacci?)
2
Saxegothaea (Podocarpaceae)
wind
pollen
Yes, indistinct
0
Ephedra (Gnetales)
insect
pollen
No, inaperturate
0
Gnetum (Gnetales)
insect
pollen
No, inaperturate
0
Welwitschia (Gnetales)
Insect
pollen
Yes, distal sulcus
0
Cycas
wind
pollen
Yes, distal sulcus
0
Zamia
insect
pollen
Yes, distal sulcus
0
Angiosperms (summary)
generalized
pollen
Yes, variable number and shape
0
1
Cupressaceae s.l. refers to a clade comprising Cupressaceae, “Taxodiaceae”, Taxaceae, Cephalotaxaceae, and Sciadopitys
Shape
rounded?
boatshaped?
boatshaped
rounded?
rounded?
rounded?
boatshaped?
boatshaped
rounded
rounded?
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
rounded
boatshaped
rounded
boatshaped
boatshaped
boatshaped
rounded?