Plant Diversity Numero Uno
Lab 6
BIOL 171
Introduction
First land plants were related to green algae – 500
million years ago
Plant Life Cycles
• All land plants have a common sexual reproductive
life cycle called alteration of generations
• Gametophyte – haploid (n) generation
• Sporophyte – diploid (2n) generation
• One generation is always dominant (more
conspicuous)
– In the Bryophytes (mosses and liverworts) the
gametophyte is dominant
– In all other land plants the sporophyte is
dominant
Alternation of Generations
(also look at figure 2 in lab manual)
Alternation of Generations Vocab
• Spores – (n) produced by the sporophyte generation through meiosis
– germinate (undergo mitosis) to produce the gametophyte (n)
• Sporangium – a protective nonreproductive jacket that contains the
spores
• Gametes – produced inside the gametangia located on the
gametophyte
– Eggs (n) are produced inside the archegonia through mitosis
– Sperm (n) are produced inside the antheridium through mitosis
• Zygote – (2n) formed by fusion of the gametes, this is the first stage
of the sporophyte generation
•
Note: the archegonia and antheridium may occur simultaneously in the same
gametophyte, but on difference branches.
Non-vascular Plants
• 3 Phyla:
– Bryophyta (mosses)
– Hepatophyta (liverworts)
– Anthocerophyta (hornworts)
• Small plants, lacking vascular tissue (specialized cells for
transport of material)
• The gametophyte generation is dominant and conspicuous
plant.
• Restricted to moist habitats
– Because they lack vascular tissue
– And because this enables their mobile sperm to swim and
fertilize the egg
• Have a cuticle, but lack stomata on the surface of the thallus
(plant body)
Bryophyta (mosses)
• Most common group
• Occurs in moist environments, but also found
in dry habitats that are periodically moist
Peat moss (Sphagnum)
Hepatophyta (liverworts)
• Flattened and lobed thallus (plant body)
• Early herbalists believed that these plants were could treat
liver disorders. (based on the doctrine of signatures)
• Found along streams on moist rocks
• Very small
Liverwort body form
• Rhizoids – root-like extensions on the lower surface of the
thallus
• There are pores on the leaf-like thallus that function in gas
exchange, but lack guard cells so are always open.
• Gemmae cups are located on the upper surface of the
thallus, they are circular cups that contain flat disks of
green tissue called gemmae.
• The gemmae are washed out of the cups when it rains, and
they grow into new, genetically identical liverworts.
(asexual reproduction!)
Seedless Vascular Plants
• Two phyla:
– Lycophyta (club mosses)
– Pterophyta (ferns, horsetails, whisk ferns).
• Depend on water for external fertilization and
development of the unprotected, free-living embryo.
• Lived in vast swampy areas during the Carboniferous
period, but declined as Earth became drier.
• The fossilized remains of the swamp forests are the
coal deposits we mine and use today.
Seedless Vascular Plants
• All have vascular tissue (specialized for conducting
water, nutrients, and photosynthetic products).
• Alternation of generations where the sporophyte is
dominant and the gametophyte is usually
independent of the sporophyte.
• These plants have stomata and structural support
tissue.
• Still retain primitive feature of motile sperm that
requires water for fertilization, thus the
gametophyte is small and only in moist habitats
Lycophyta (club mosses)
• Found in moist habiats (i.e. bogs, streamsides)
• One species of Selaginella, the resurrection plant,
lives in deserts!
• Produce two kinds of spores (heterospory).
– Megaspores – large spores that produce female
gametophytes
– Microspores – small spores that produce male
gametophyte
Lycopodium
strobili
sporophyte
microspores
megaspores
Pterophyta
(ferns, horsetails, whisk ferns)
• Until recently these three groups of seedless vascular
plants were placed in separate divisions: Pterophyta
(ferns), Sphenophyta (horsetails), and Psilophyta
(whisk ferns).
• New molecular evidence has shown that they are all
closely related, thus they are all now in the division
Pterophyta.
Psilophytes (whisk ferns)
• Small, dichotomously
branched (repeated
Y-branches),
photosynthetic stems
that reproduce by
aerial spores.
• Found today in some
areas of Florida and
in the tropics.
Sphenophytes
strobili
Sphenophytes (horsetails)
• Have green jointed stems with occasional
clusters of leaves or branches.
• Their cell walls contain silica that give the
stem a rough texture.
• Occasionally used by pioneers to scrub dishes
– thus they were commonly called the
scouring rushes.
• In cooler regions of North America they grow
as weeds along roadsides.
Pterophyta (ferns)
• Most successful group of
seedless vascular plants.
• Occupy habitats from the
desert to tropical rain
forests.
• Most are small plants that
lack woody tissue, except
the tree ferns found in
tropical regions.
rhizome
roots