These notes will cover two lecture periods.
1) Evolution
a) Best living model for first "land" plant is the green algae - Coleochaete - complex multicellular shoreline algae. This is haploid.
b) Evolutionary trend for increasing dominance of the sporophyte (diploid) generation.
c) Primitive vascular plants present in the Silurian - 438 to 408 million years b.p. Much radiation in the Devonian - 408 to 360 million years b.p.
2) Vascular plant body
a) root system - anchors and absorbs water and nutrients
b) shoot system - stems and leaves involved in photosynthesis
c) tissues - dermal, vascular and ground
d) primary growth - apical meristems
e) secondary growth - vascular cambium (secondary xylem and phloem) and cork cambium (corky periderm)
f) vascular cells
i) tracheary elements - trachieds and xylem vessel members - dead when functional
ii) phloem cells - living protoplasm when functional
g) stele - primary xylem and phloem
i) protostele - no pith, no leaf gaps
ii) siphonostele - pith, may have leaf gaps
iii) eustele - ptih, discrete vascular strands
h) leaves
i) microphylls - single vascular strand, no leaf gaps
ii) macrophylls - complex venation, leaf gaps
3) Reproduction
a) Oogamy - large cell - egg, small cells - sperm
b) Heteromorphic alternation of generations - haploid (1N, gametophyte) looks very different from diploid (2N, sporophyte)
c) Generalized life cycle
i) 2N sporophyte - sporangia - spore mother cells undergo meiosis to produce 1N spores
ii) 1N spores produce 1N gametophyte
iii) gamateophytes produce 1N antheridia (sperm) and 1N archegonia (egg)
iv) sperm fertilizes egg to form 2N zygote
v) zygote develops into embryo, which develops into 2N sporophyte.
d) Evolutionary trend toward progressive reduction in size of gametophyte and toward its nutritional dependence upon the sporophyte generation.
4) Major living Divisions of Seedless Vascular Plants
a) Rhyniophyta, Zosterophyllophyta and Trimerophyta - three simple primitive extinct Divisions. See phylogenetic reconstruction in your text.
b) Psilotophyta - wisk-ferns
i) Psilotum, lacks both roots and leaves, sporophyte dichotomously branched, underground endosymbiotic rhizome
ii) Life cycle = 1N spores produced by sporophyte by meiosis in sporangia, spores germinate to form bisexual gametophyte, looks like rhizome and has endosymbiotic fungus, sperm swim from antheridia to archegonia and fertilize the egg, the zygote grows to initiate the new sporophyte, and is anchored to the gametophyte by the "foot" - absorbs nutrients from gametophyte. Sporophte eventually outgrows its dependence upon the gametophyte.
c) Lycophyta - ground-pines
i) "Lycopodium" group - homosporous, microphylls and sporophylls (may be grouped into strobili).
ii) Life cycle - gametophyte bisexual, either green or non-pigmented subterranean (endosymbiotic). Sperm swim to egg and fertilize it after neck canal cells break down. Zygote grows into sporophyte, anchored by the "foot".
iii) "Selaginella" group - heterosporous, ligules present at base of microphylls
iv) Life cycle - megagametophyte (female) with archegonia and rhizoids, cast on soil, microgametophyte (male), with spermatogenous tissue, also cast on soil, egg develops in archegonia, sperm develop in microgametophyte, sperm swim to egg, fertilize egg, zygote pushed deep into the megagametophyte by suspensor, anchored by "foot". Young sporophyte grows out of megagametophyte.
d) Sphenophyta - horse-tails, scouring rushes
i) Equisetum - homosporous, leaves reduced to scales, hollow, silicaceous stems, may be oldest genus on earth.
ii) Life cycle - sporophyte may have separate vegetative and reproductive shoots, sporangia in strobili at tip of stem, sporangiophores are umbrella-like, elators help disperse haploid spores, which germinate to produce bisexual, green, free-living gametophyte, sperm swim from antheridia to archegonia, fertilize egg, zygote develops into new sporophyte, anchored by "foot"
e) Pterophyta - ferns and water ferns
i) Many genera, main distinction between primitive homosporous eusporangiate ferns (Ophioglossales and Marattiales) and the more advanced homosporous leptosporangiate ferns (Filicales), eusporangium - sporangia develops from many initial cells via cell division parallel to surface, leptosporangium - sporangium develops from a series of divisions in a single initial cell, both parallel and perpendicular to the surface. Leptosporangia usually stalked. Water ferns are heterosporous.
ii) Eusporangiate ferns - example Botrychium (grape fern), single leaf from rhizome each year, leaf has vegetative and fertile segments, fertile segments bear eusporangia, gametophyte is elongate, subterranean, and rhizome-like, antheridia on top, archegonia on sides
ii) Filicales (leptosporangiate ferns) - most common ferns, sporophyte fronds develop, usually via circinate vernation, bear leptosporangia in sori on fertile fronds, sori may or may not be covered by a structures called indusia, spores develop into bisexual, green, free-living, rhizoid-laden, heart-shaped gametophytes, sperm swim to egg, fertilize egg, zygote develops in gametophyte, anchored by "foot"
Note - some (apogamous) ferns living in dry areas produce new sporophytes directly from structures that develop from 2N spores, looks like gametophyte, but is diploid (sporogenous cells do not undergo meiosis), eliminates the need to sperm to swim to egg.
iii) Water ferns - Marsiliales and Salviniales, aquatic, heterosporous, derived from terrestrial ancestorsa) Marsilia - rhizomes, aquatic, clover-like leaves, sporocarps (bean like resistant 2n spores) germinate in water to form chains of sori, each sorus contains rows of microsporangia and megasporangia
b) Azolla and Salvinia - float on surface, sporangia in sporocarps, Azolla - leaf pouch contains cyanobacteria, nitrogen-fixing, important in rice paddies, Salvinia - two leaves green and photosynthetic, one leaf dissected and bearing sporangia, hangs down into the water.