Fern Morphology and Life Cycle Plant Biology 209 January 14, 2014 Version 140116
Jan 20, 2016
Fern Morphologyand Life Cycle
Plant Biology 209
January 14, 2014
Version 140116
Megaphylls
Siphonosteles
Spore dispersal
Five lineages are included in the monilophyte clade:
• Equisetophytes (horsetails)
• Psilotales (whisk ferns)
Three of them are considered “ferns”:
•Marattiales •Ophioglossales (grape ferns)•Polypodiales
Sporophyte(2n)
Gametophyte(n)
Blueprint: the Land Plants Life Cycle
-74
The Sporophyte PhaseThe Sporophyte Phase
Sporangia
Vegetative Body: the StemCHARACTERISTICS
VARIATION
POLYPODIALES SEED PLANTS
apical meristem with a single tetrahedral apical initial cell
Many initials
stem protoxylem in islands Stem protoxylem primitively continuous
buds not axillary (buds in other positions)
Buds axillary
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 StemVARIATION
• 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 Havea Creeping Rhizome
Rhizome habit: is the underground stem ± upright or is it long-creeping?
long-creeping
more or less upright
Tree ferns have erect stems.
A B C D
Variations on the siphonostele
B,C, and D are dictyostelic siphonosteles because their leaf gaps overlap
Indument: of hairs, scales, or both
Osmunda Woodsia Dryopteris
Indument of Hairs(Lophosoria)
Indument of Scales(Dryopteris)
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)
Walking fern(leaf entire)
Christmas fern(leaf once-pinnate)
Lady fern(leaf twice-pinnate
pinnatisect)
LeafDissection
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 purple-stemmed 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.
Spore Catapult Video
Leptsporangium Structure and Dehiscence
Sporangium development
tapetum
tapetum
Trilete spore(e.g., Adiantum)
Monolete spore(e.g., Polystichum)
Fern spores are either trilete or monolete
Trilete sporeJamesonia imbricata
Monolete sporeLomariopsis guineensis
Fern spores are either trilete or monolete
The Gametophyte Phase
spore wall
rhizoid
Spore germination and early growth, Ceratopteris
General Features of Fern Gametophyte Development
Fern sperm are helicaland multiflagellate
Antheridia
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