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