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SEEDLESS VASCULAR PLANTS
I. Vascular plants
A. contain true conducting tissues, xylem and phloem
II. Two major groups of vascular plants:
A. Seed plants - reproduce via seeds
1. Seed = a structure in which the embryo (the young sporophyte) is shed
from the parent plant, enclosed within a resistant coat, together with a
supply of food that aids its establishment
2. The majority of extant plants are seed plants
B. Seedless plants - reproduce via spores
III. There are three phyla of extinct seedless vascular plants
A. The genera Rhynia, Zosterophyllum and Trimerophyton
are members of these phyla
B. The earliest known go back about 425 million years ago and most went
extinct by about 370 million years ago
C. They were relatively simple plants 18 in to 36 inches tall
1. Naked photosynthetic stems
2. Mostly terminal sporangia (some lateral)
3. No roots or leaves
4. All homosporous
5. Protosteles
EXTANT PHYLA OF SEEDLESS VASCULAR PLANTS
There are two phyla of extant seedless vascular plants. They
are often called ferns and allies
I. Phylum Pteridophyta - ferns
A. The majority of extant seedless vascular plants belong to this phylum
B. About 11,000 species, most of which are tropical
C. Most of the fern plant you see is actually leaves, called fronds. The
fronds are borne from a horizontal stem called a rhizome.
D. Ferns go back to before the Carboniferous period, about 360 million
years ago, and they were a large component of coal age forests
E. Ferns are quite diverse and range in size from 1 inch in diameter (water
ferns) to tree size in New Zealand (tree ferns). Although they are called tree
ferns all growth is primary so they are not true trees. Only one genus, Botrychium,
the grape fern actually has a vascular cambium
F. Major characteristics of the Pterophyta:
1. Most have a siphonostele
2. The leaves, called fronds, are megaphylls. The leaves are coiled in
bud forming "fiddleheads"
3. Most are homosporous. A few water ferns and many extinct species
are/were heterosporous
4. Sporangia are usually borne in clusters called sori (sorus) on the
underside of the leaves
a. In a few species they may occur on separate fertile stalks
b. Sori may be covered by a flap of tissue called an indusium, cross
section
5. Sporangia are stalked and they have a thick walled layer called an
annulus which aids in spore dispersal
6. They have free living, usually heart shaped, bisexual gametophytes
called prothalli (prothallus), which bear archegonia and antheridia (usually
at different times to promote outcrossing). The sporophyte remains attached
to gametophyte for a while
7. They have multiflagellated sperm and require water for fertilization.
G. See your text for a typical fern life cycle.
II. Other Pteridophyta
A. Psilotales
1. 2 genera and about 10 species
2. Psilotum, the whisk fern, is native to the
southern U.S. from Florida to Arizona and Puerto Rico
3. Psilotum is the simplest vascular plant, it is
hardly different from the extinct ones:
a. No roots or leaves
b. A simple dichotomously branched photosynthetic stem
with scale like outgrowths
c. Rhizome (horizontal underground stem)
d. Homosporous and the spores are borne in sporangia on
short lateral branches
e. Protostele
f. Multiflagellated sperm requiring water for
fertilization
4. See your text for the life cycle of Psilotum
B. Equisetales - horsetails, scouring rushes or snake grass
1. Only one extant genus, Equisetum (Equus, horse; seta,
bristle), with about 15 species
2. Common in North America
3. Temperate species range up to 4 feet tall, tropical species may be up
to 15 feet tall, with stems up to 1 inch diameter
4. The phylum goes back at least 300 million years ago. Extinct calamites
(giant horsetails), were up to 50 feet tall, and they were a major component
of coal age forests
5. Major features:
a. Hollow, jointed, ribbed stems with siliceous deposits in the
epidermal cells. The silicone deposits give the stem a rough texture. They
used to be used for scouring pots and pans, hence the common name scouring
rushes
b. Photosynthetic stems with sunken stomata
c. The stems have very well defined nodes and internodes
d. Internally the stems have a central hollow pith surrounded by a ring
of smaller canals. Each of the smaller canals is associated with a strand
of primary xylem and primary phloem
e. The leaves are very reduced to scales, which are interpreted as
being reduced megaphylls
f. Homosporous and the sporangia are borne in a strobilus, on umbrella
shaped sporangiophores
Spores have elaters - hygroscopic appendages which aid in dispersal
Strobili may be borne at the tips of a vegetative axis, or borne on a
non-chlorophyllous fertile branch that develops from the rhizome
g. Gametophytes are green and free living. They may be either bisexual
or male. In bisexual ones the archegonia develop before the antheridia to
ensure outcrossing
h. The sperm are multiflagellated and water is required for
fertilization
6. The life cycle of Equisetum is on p. 404 of your text
III. Phylum Lycopodiophyta - commonly called club mosses, spike
mosses, quillworts or ground pines
A. 10 - 15 extant genera and about 1,000 species
B. They are relatively small plants, up to 2 feet high
C. The genera Lycopodium and Selaginella are fairly common in
North America
D. Most are hardy perennials which occupy forest floors, but a few are
tropical epiphytes
E. Extinct giant club mosses, up to 100 feet tall, were major components of
the Coal Age (Carboniferous) forests, 360-286 million years ago
F. Major characteristics:
1. Microphylls
2. Protosteles
3. There are both homosporous (Lycopodium) and heterosporous (Selaginella)
genera
4. Sporangia are borne in the axils of leaves called sporophylls
a. Sporophylls may be arranged into a cone-like structure called a
strobilus (strobili)
5. Flagellated sperm which require water for fertilization
G. The life cycles of Lycopodium and Selaginella are in your
text. Note how they differ because one is homosporous and
the other is heterosporous
H. Members of the genus Selaginella have a ligule, a small
protuberance at the base of the leaves
I. Members of the genus Isoetes (quillworts) are unusual looking
aquatics of lakes, ponds, rivers, swamps, and vernal pools. There are a few
terrestrial species.
1. The heterosporous sporophyte consists of many quill like leaves
spirally arranged on a very shortened axis
2. Although the leaves may reach 2 feet long, they are still microphylls
with a single vascular trace and no leaf gaps
3. A ligule is also present
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