Weber State University      Department of Botany

                                                    BOTANY  LS1203 - PLANT  BIOLOGY

Seedless Vascular Plants

Ferns (Pterophyta or Polypodiophyta)
Horsetails (Sphenophyta or Equisetophyta)
Whisk Ferns (Psilotophyta)
Club Mosses (Lycophyta)

Sporophyte is dominant generation; gametophyte is smaller, but nutritionally independent.  Gametophyte forms antheridia and archegonia to produce sperm and egg, respectively.

As members of the Plant Kingdom:  chl a, chl b, sporic life cycle, starch storage in plastids

Vascular Tissue
    allows upright growth on land
    large leaves
    roots for anchorage and absorption of soil minerals and water

Control of plant water status:  close stomata when transpiration rate exceeds water uptake rate by roots.

Features:
1)  sporic life cycle
2)  eggs in archegonia; sperm in antheridia
3)  chl a, chl b, carotenoids, starch, cellulose walls
4)  flagellated sperm; water required for fertilization
5)  well developed cuticle; functional stomata
6)  xylem and phloem
7)  lignin
8)  independent sporophyte and gametophyte; sporophyte is dominant generation
9)  sporophyte can be long lived


Sporophyte: Reproduce asexually by growing new leaves out of the rhizome each year
Both gametophyte and sporophyte can reproduce asexually by fragmentation

Some of the seedless vascular plants produce a strobilus = a step tip with several closely spaced leaves with sporangia.  e.g. club mosses, horsetails.  Forerunner of the cones of conifers and the flower.

Whisk Fern (Psilotum)

no roots; have rhizomes with absorptive rhizoids; mycorrhizae
no obvious leaves; sporangia are little balls near stubs where you would expect leaves
photosynthetic stems, dichotomous branching
homosporus


Club Mosses (Selaginella,  Lycopodium [resurrection fern])

have strobili (the “club” part)
some are heterosporus (Selaginella)
    microspores form the ♂ gametophyte
    megaspores form the ♀ gametophyte
some are homosporous (Lycopodium)
this group also includes the quillworts (Isotes); some species of quillworts have CAM photosynthesis



Horsetails (Equisetum)

Equisetum is the only living genus; 15 known species.
Silica in the cell walls  ==>  scouring rush
found worldwide in moist habitats, including the damp areas on lower campus near the Social Sciences building

Has true stems, roots, and leaves, but the leaves are very reduced.  The stem is the primary photosynthetic organ of the sporophyte.

Homosporus. The spores have attached elaters.  Sporangia in a terminal strobilus.



Ferns

the largest group of seedless vascular plants
circinate vernation = the curling of young fern leaves (fronds), i.e. “fiddleheads”

no strobilus.  Spores form on leaves in structures called sori.  Some sori are covered by an indusium.  The leaves with sori are often called sporophylls.

mostly homosporus.  Azolla (water fern) is heterosporus.

spore ---->  protonema ---->  heart-shaped gametophyte with archegonia and antheridia on the underside  ----->  water required for sperm to swim to egg  ----->  zygote  ---->  sporophyte grows attached to gametophyte  ---->  adult fern sporophyte ---->  sporangia clustered in sori on undersides of leaves ---->  spores



Uses

Lycopodium - flash powder
Azolla + Anabaena (a cyanobacterium) - N-fixation in rice paddies
Equisetum - scouring
various ferns - the floral industry as house plants, ornamentals
fossil fuel deposits (from the Carboniferous period, roughly 360-290 million years ago)

 

Review

What are the similarities and differences between the ganetophytes of the bryophytes and the seedless vascular plants?
What are the major differences between the four phyla of seedless vascular plants?
What similarities are found in the four phyla of seedless vascular plants?
What features of seedless vascular plants are found in all members of the Plant Kingdom?
What features of seedless vascular plants are found in all vascular plants but not in the bryophytes (or are not well developed in the bryophytes)?
Be familiar with the terminology:  homosporus, heterosporus, strobilus, antheridia, archegonia, gametophyte, sporophyte, microspore, megaspore, transpiration, cuticle, stomata, xylem, phloem, circinate vernation, sori, sporophylls
How are a spore and a gamete similar?  How are they different?

Suggested Online Reading

Introduction to the Psilotales: the whisk ferns  and Introduction to the Sphenophyta (University of California Berkeley Museum of Paleontology)

Psilophyta, Lycophyta, Sphenophyta, and Pterophyta   (Michael Knee, Ohio State University)

Biological Diversity:  Nonvascular Plants and Nonseed Vascular Plants  (from the Online Biology Book by M.J. Farabee at Estrella Mountain Community College) 

Lower Vascular Plants   (Ross Koning at Eastern Connecticut State University) 

Seedless Vascular Plants  (Steven Wolf at California State University Stanislaus) 

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27 September 2002.  Links checked 23 Nov 04.