Fern Morphology and Life Cycle Plant Biology 209

Fern Morphology
and Life Cycle
Plant Biology
209
January 14, 2014
Version 140116
Spore dispersal
Siphonosteles
Megaphylls
Five lineages are included in the
monilophyte clade:
• Equisetophytes (horsetails)
• Psilotales (whisk ferns)
Three of them are considered “ferns”:
•Marattiales
•Ophioglossales (grape ferns)
•Polypodiales
Gametophyte
(n)
-74
Sporophyte
(2n)
Blueprint: the Land Plants Life Cycle
The Sporophyte Phase
The Sporophyte Phase
There are four plant organs:
I. The Vegetative Body:
A.The Shoot:
1. Stem
2. Leaf
B. The Root
II. The Reproductive Body: Sporangia
Flowers (= Leaves + Sporangia)
Vegetative Body: the Stem
CHARACTERISTICS
POLYPODIALES
SEED PLANTS
apical meristem with a single
tetrahedral apical initial cell
Many initials
stem protoxylem in islands
Stem protoxylem primitively
continuous
VARIATION
buds not axillary (buds in other Buds axillary
positions)
stem vascular tissue in a
siphonostele (at least not a
eustele)
Stem vascular tissue in a
eustele
wood (and cambium) absent
Cambium present
POLYPODIALES
SEED PLANTS
apical meristem with a single
tetrahedral apical initial cell
Many initials
stem vascular tissue in a siphonostele
(usually)
POLYPODIALES
SEED PLANTS
Vegetative Body: the Stem
VARIATION
• Stems creeping or erect (tree ferns - but no wood!)
• Siphonostele varies in compaction of leaf gaps.
• Epidermal coverings (indument) are hairs or scales.
Our New England Ferns Have
a Creeping Rhizome
more or less upright
long-creeping
Rhizome habit: is the underground stem ± upright or is it
long-creeping?
Tree ferns have
erect stems.
Variations on the siphonostele
A
B
C
D
B,C, and D are dictyostelic siphonosteles because their leaf gaps overlap
Indument: of hairs, scales, or both
Osmunda
Woodsia
Dryopteris
Indument of Scales
(Dryopteris)
Indument of Hairs
(Lophosoria)
Variation in petiole scales of scaly tree ferns (Cyatheaceae)
Indument of Hairs and Scales (Phegopteris)
Vegetative Body: the Leaf
• The fern leaf is a
megaphyll
• Vernation is
circinate
The Frond (Leaf)
Fiddleheads (croziers)
Leaf
Dissection
Lady fern
(leaf twice-pinnate
pinnatisect)
Walking fern
(leaf entire)
Christmas fern
(leaf once-pinnate)
Reproductive Body: Sporangia
• Sporangia are commonly borne in clusters
called sori
• They are of the leptosporangiate type
• They are often covered by an indusium.
• Sori vary in shape and position.
The sorus of Cyrtomium from above, covered by its true indusium
Marginal sori of purplestemmed cliffbrake
Abaxial sori of Polypodium
Fern sori differ in shape, position, and presence
or absence of an indusium
Leptosporangia
- Sporangia small (ca 0.25 mm in diameter)
- Sporangial walls one cell layer thick plus
tapetum
- Sporangia develop from a single sporangial initial
- Sporangia produce relatively few spores (commonly 64)
Eusporangia
- Sporangia large (> 0.5 mm in diameter)
- Sporangial walls several cell layers thick
- Sporangia develop from a group of
sporangial initials
- Sporangia produce a large number of spores.
Leptsporangium Structure and Dehiscence
Spore Catapult Video
Sporangium development
tapetum
tapetum
Fern spores are either trilete or monolete
Trilete spore
(e.g., Adiantum)
Monolete spore
(e.g., Polystichum)
Fern spores are either trilete or monolete
Trilete spore
Jamesonia imbricata
Monolete spore
Lomariopsis guineensis
The Gametophyte Phase
Spore germination
and early growth,
Ceratopteris
rhizoid
spore wall
General Features of Fern Gametophyte Development
Antheridia
Fern sperm are helical
and multiflagellate
from Raven…
The transition from zygote to embryonic sporophyte
From Raven
Stable (versus labile)
characters of the
Polypodiales:
•
•
•
•
Stems have siphonosteles (most species)
Apex has a single tetrahedral apical initial
Leaves are megaphylls with circinate vernation (croziers)
Sporangia usually abaxial (on the lower surface, i.e. away
from the stem), leptosporangiate, in sori (most species)
• Gametophytes are green and thallose (that is broad and
flat), not axial (that is with an elongating meristem).
First characters to evaluate in the
ferns:
•
•
•
•
•
•
Stem habit: erect or creeping, long internodes or short?
Leaf shape: broadest at base, middle, above middle?
Leaf dissection: once-pinnate, twice pinnate, etc.
Indument: of hairs, scales, or both?
Sorus shape and position: round and near margin, etc.
Indusium: present or absent