BIO
201: Botany
SEEDLESS
VASCULAR PLANTS
GENERAL CHARACTERISTICS
1)
presence of true vascular tissue:
a) true stems
horizontal
stem = rhizome
vertical
stem = trunk
b) true leaves = photosynthetic tissue with vascular bundles
microphylls
(single unbranched bundle)
megaphylls
(branched vascular bundles)
c) true roots
include
branching roots of a main (tap) root = adventitious
2) sporangia typically associated with leaves = sporophyll
3)
alternation of generations but sporophyte much larger
presence of vascular tissues has allowed larger size
4) no seeds
TAXONOMY - Four Divisions/Phyla are currently recognized. We will look at three:
Division
Lycophyta - lycopods
1) microphylls only
2) each sporangium associated with a sporophyll & one sporangium per
sporophyll
Division Equisetophyta - horsetails
1) microphylls, but not photosynthetic
2) sporangia at stem tip without associated leaf tissue
= strobilus
Division
Polypodiophyta - ferns
1) megaphylls
2) many sporangia per sporophyll
DIVISION LYCOPHYTA (lycopods)
We will look at three genera
General
characteristics
microphylls only
sporangia on unmodified (or slightly modified) sporophylls
Lycopodium:
club moss, running cedar (pp. 391-393)
tropical and temperate genus of moist forests
many grow as epiphytes in tropics
leaves small & scale-like
sexual reproduction -- sporangia found in one of two patterns:
1) in axils of unmodified sporophylls
2) in axils of slightly modified sporophylls and on elongate stems =
Strobilus (fig 21.3)
all spores of same size = Homosporous
gametophyte -- very small and tuber-like
some grow on surface and are photosynthetic
some subterranean and nonphotosynthetic, fungal
hyphae commonly associated
monoecious- antheridia & archegonia on surface (same plant)
sperm must have free water to swim to archegonium
Selaginella:
spike moss (pp. 394-395)
stems with four rows of microphylls - 2 large, 2 small
= Anisophyllous
sexual reproduction
sporangia always clustered into strobili
spores of two distinct sizes = Heterosporous
1)
microspores - small, many per sporangium
develop
into male gametophyte
in
microsporangia
2)
megaspores - large, typically 4 per sporangium
develop
into female gametophyte
in
megasporangium
Why heterospory?
1)
may mean dioecious - guarantees cross fertilization
2)
larger female to give nutrients to developing embryo
larger means more nutrients
small male only produces sperm which promptly leave
gametophytes develop within spore wall
nonphotosynthetic,
dioecious
male- jacket layer + sperm (with flagella)
female- cellular, may have rhizoids + several archegonia
Isoetes:
quillworts (pp. 395-396, fig 21.7)
aquatic
very elongate microphylls
very short stem in ground = Corm
sporangia produced at base of sporophylls - heterosporous
DIVISION EQUISETOPHYTA (horsetails)
Single genus Equisetum -- horsetails (pp. 396-399)
Sporophyte
(fig 21.10):
rhizome present
stems cylindrical, hollow, jointed
leaves scale-like, nonphotosynthetic
strobili produced - homosporous
sporangia on small stalked structures = Sporangiophores
spores with attached elators (note drawing, fig 21.13)
Gametophyte:
globular with rhizoids 1mm -
1 cm in length
photosynthetic
bisexual or male only
DIVISION POLYPODIOPHYTA (ferns)
Differences
from lycopods & horsetails:
1) Megaphylls - leaves with branching vascular bundles
2) sporangia produced directly on the leaf
3) typically many sporangia per leaf
Sporophyte
structure (variety of pictures, p. 402):
Both horizontal and vertical stems
horizontal = Rhizome; vertical = Trunk
all species in SC have rhizomes -- tree ferns in tropics
(such as fig 12.26)
all roots produced are adventitious
results
in a very interesting morphology on trunks
Leaves
are correctly called Fronds - since they have two functions (fig.
21.17)
1) photosynthetic
2) reproductive
Photosynthetic portion with 2 basic parts
1) petiole
2) blade - photosynthetic + sporangium producing tissue
a)
entire = Simple
b)
divided, Rachis (central stalk) & Pinnae (blade)
= Compound
young fronds unroll as they develop = circinate vernation (fig.
21.19)
fronds
called Fiddleheads
Spore production
all but a few ferns are homosporous
sporangia clustered into Sori (s. = sorus) - fig. 21.20
appear
as brown spots on lower surface of frond (fig. 21.20b)
may have an associated protective tissue = Indusium (fig. 21.20c,f)
diversity of sorus and indusium types:
1)
sori without indusia = naked (fig21.20b)
2)
sori at frond margin with margin folded over
3)
sori a center of frond tissue with one sided indusium (fig 21.20d)
4)
sori at center of frond tissue with umbrella-like indusium -- sporangia attached to indusium
5)
highly modified frond with only sporangia tissue =
dimorphic fronds (fig. 21.17b)
sporangium morphology:
elongate
stalk, disc-like apex (like a frying pan) - fig. 21.21
flattened
cells on each surface
squared
cells around outside edge (annulus + lip cells)
the annulus
cells around edge are hygroscopic
1) slow opening due to slow drying
2) springing forward after overextending
Spore development:
Spore Mother Cells (2n) divide by meiosis to form a tetrad of spores (1n)
Gametophyte: =
Prothallus (fig 21.22)
small- less than 2 cm
typically heart-shaped, photosynthetic, with rhizoids
most species are monoecious
but
antheridia & archegonia do not mature at same time
antheridia - multicellular, jacket layer
sperm
multiflagellate
archegonia - found near notch, flask-shaped, ventor + 1 egg
Initial sporophyte development is dependent on gametophyte