Topic 5: Seedless Vascular Plants (Ch. 29)

I. Vascular Plants (overview) – plants with xylem and phloem – 7 to 9 living phyla, depending on who you talk to

A. able to dominate most terrestrial habitats because of vascular tissues, waxy cuticle, and stomata

B. conducting tissues (xylem and phloem) called vascular tissues

1. cylindrical or elongated cells that form network throughout plant

2. xylem

· conducts water and dissolved minerals upward

· typically dead cells

· typically at least partially lignified (having lignin, a highly branched polymer that makes cell wall more rigid)

3. phloem

· transports carbohydrates in solution throughout plant (down and up)

· living cells

4. only with vascular tissue do you have true leaves, stems, and roots

C. sporophyte dominant

D. vascular tissue is usually only found in the sporophyte generation

E. seeds (when present) are highly resistant structures that increase ability of developing embryos to survive on land

F. divided into seedless and seed-forming groups; seed-forming phyla covered in future outlines

II. Seedless Vascular Plants (ferns and fern allies)

A. sporophyte dominant and can grow independent of gametophyte in all

B. gametophyte small, reduced, but still able to grow independent of sporophyte in all

C. importance: dominated land during Carboniferous Period (354-290 million years ago), becoming a source of coal

1. coal is incompletely decomposed, highly compressed, carbon-rich rock derived mainly from the bodies of ancient seedless vascular plants (a type of “fossil fuel”)

2. fossil coal swamps are full of extinct plants

3. coal is a vital source of energy; burned for heat and for producing electricity (over half of U.S. electric production)

D. at least 3 extinct phyla represented in the fossil record; one will be covered, Phylum Rhyniophyta

E. 4 phyla with living members

1. Phylum Lycophyta

2. Phylum Pterophyta

3. Phylum Psilophyta (some group with Pterophyta; do fall in a clade with that group and Arthrophyta)

4. Phylum Arthrophyta (some group with Pterophyta; do fall in a clade with that group and Psilophyta)

III. extinct Phylum Rhyniophyta – oldest vascular plant fossils (Cooksonia, 420 MYA)

A. branching axis; no leaves or roots

B. only a few centimeters tall

C. sporangia at ends of branches

D. appearance much like that of modern-day whisk ferns

E. homosporous – only one spore type, so only one gametophyte type

IV. Phylum Lycophyta – club mosses

A. ~1000 living species; worldwide, but most in tropics and moist temperate regions; many species endangered

B. includes “resurrection plants”

C. fossil record includes tree-like forms that died out about 270 MYA

D. apparently evolved separately from the other seedless vascular plants

E. small, resembling mosses (but vascular with dominant sporophyte)

F. leafy stems usually less than 30 cm long

G. their leaves are also called microphylls, with very little vascular tissue (just a single vein); other vascular plant leaves have much more complex vascular tissue networks

H. homosporous and heterosporous genera

1. heterosporous – plant makes two types of meiospores, resulting in two types of gametophytes

2. megaspore is larger of the two; grows via mitosis into the female gametophyte

3. microspore is smaller of the two; grows via mitosis into the male gametophyte

I. sexual reproduction similar to that of ferns

J. sporangia grow from specialized leaves called sporophylls; sporophylls are clustered in a cone-like strobilus

V. Phylum Pterophyta – ferns

A. somewhat complicated phylogeny; we will visit the tree of life in class to discuss this

B. fossils date to as long as 375 MYA (important fossil fuel source)

C. ~12,000 living species; throughout world, but ¾ of species tropical

D. most leafy, but some tree ferns

E. most are homosporous, but some are heterosporous

F. life cycle similar to moss except decreased gametophyte, independent and dominant sporophyte

1. gametophyte

· germinating spore divides by mitosis and forms multicellular protonema

· protonema grows into mature gametophyte called prothallus

§ typically heart-shaped; mostly one-cell thick

§ has rhizoids

2. gametes produced in male antheridia and female archegonia on same or separate prothalli

3. sperm made in antheridia swim to archegonia (using flagella; need outside water source to swim in)

4. sperm unites with egg, forming diploid zygote

5. zygote undergoes mitotic divisions and develops into sporophyte

· sporophyte grows out gametophyte and takes over (larger, vascular, photosynthetic, responsible for all of own nutrition)

· typically have horizontal, underground stem (rhizome)

· leaves (called fronds) develop from rhizome as coiled “fiddleheads”

· form stalked sporangia in clusters called sori, typically on the backs of fronds

6. spore mother cells in sporangium produce haploid spores

7. at maturity, outer covering of sporangium snaps off, catapulting spores

8. spore in right (mainly moist) environment will germinate

VI. Phylum Psilophyta – whisk ferns

A. probably form a monophyletic group with ferns and horsetails; some group these within the fern phylum

B. simplest living vascular plants

1. no true roots or leaves – leaf-like enations and such sometimes present

2. forking green stems (photosynthetic; true stems)

C. sexual reproduction much like ferns (have antheridia and archegonia, swimming sperm that need outside water, etc.)

D. all are homosporous

E. like ferns, sporophyte is dominant generation

F. gametophytes small, colorless

1. in soil beneath sporophytes

2. associated with fungi

3. saprobic or parasitic

4. some have elements of vascular tissue (only gametophytes known to have this)

G. tropical and subtropical

H. only 6 known living species

VII. Phylum Arthrophyta – horsetails (alternative phylum names: Sphenophyta; Equisetophyta)

A. probably form a monophyletic group with ferns and whisk ferns; some group these within the fern phylum

B. 15 known living species, all in genus Equisetum

C. most <1 m tall, some 3 m tall; widely scattered in damp regions throughout the world

D. fossil record back to 300 MYA

1. once much more diverse and dominant

2. fossil record includes tree-like forms as tall as 30 m

E. sporophyte dominant

1. branching underground rhizomes with roots at their nodes

2. hollow, ribbed, jointed, photosynthetic stems

3. whorls of scale-like, nonphotosynthetic leaves at nodes on stems

4. some have whorls of photosynthetic branches at nodes as well

5. stems hollow

6. silica deposits in some epidermal cells (stiffens; protects from predators)

7. some are called “scouring rushes” because they were used by pioneers for scrubbing dishes

F. most are homosporous

G. sexual reproduction similar to that of ferns

H. sporangia on underside of stalked structures called sporangiophores

I. sporangiophores are clustered in a cone-like strobilus at a stem tip