bryophytes
DESCRIPTION
bryophyesTRANSCRIPT
Bryophytes
Bryophytes
Plants are divided into two large groups
>Bryophytes - lack vascular tissue
>Tracheophytes - have vascular tissue
>Bryophytes not closely related
Phylum Bryophyta - mosses
Phylum Hepaticophyta - liverworts
Phylum Anthocerophyta - hornworts
Bryophytes share several primitive traits
>Rely primarily on diffusion
>Limited to moist environments
>Lack a true root-shoot system
>Sporophytes are not free living
Bryophytes rely on diffusion to take in water and to exchange gases
Bryophytes are usually small - inconspicuous
Advantage of being small - dont have to invest in support structures and vascular tissues
Bryophytes have a central strand of primitive vascular tissue
Not true vascular tissue, much simpler than that of higher plants
Bryophytes are limited to moist environments - no mosses in the desert
Bryophytes need water to reproduce - sperm must swim to the egg
Bryophytes lack a true root-shoot system - no true roots, stems, leaves
Have more primitive tissues that function like leaves, roots
Tiny leaves are scale like sheets only one cell thick
Roots are tiny rhizoids - a few epidermal cells that anchor the plant to the soil
The sporophytes of bryophytes are not free living organisms
The leafy green plant we think of as moss is the gametophyte generation
The sporophyte generation grows out of the tissues of the gametophyte, and depends on its parent for nutrition
Phylum Bryophyta Mosses
16,000 species, from Greek bryon = moss - Mnium, Sphagnum
Two growth types
>Cushiony moss - erect stalks
>Feathery moss - flattened mats, low-lying
Moss plants are male or female (dioecious)
Male plants have antheridia at the top
Female plants have archegonia at the top
Gametophytes are haploid, so can make gametes by mitosis
Antheridia produce sperm
Archegonia produce eggs
Sperm swims through thin film of water from the antheridium to the archegonium
Sperm drawn to the egg by chemical attractant
Sperm swims down the neck of the archegonium
Sperm fuses with egg, forms 2n zygote
The male and female plant share a cigarette, discuss old times
Diploid zygote develops into the adult sporophyte, a small green stalk growing out of the top of the female plant
Stalk can photosynthesize, but soon turns brown, lives off the parent plant (sound familiar??)
Sporophyte consists of a stalk with a small capsule on the top
Cells in capsule undergo meiosis, form haploid spores
Capsule ripens, the lid or operculum opens up, releases the spores
Spores germinate into tiny green threads called protonema (pl. = protonemata)
Looks like tiny green algae.hmmmm
Buds on protonema develop into adult gametophytes
Mosses can also reproduce asexually by fragmentation
Mosses can also grow little vegetative buds called gemmae, that break off and grow into a new plant
Mosses - Ecological Importance
Pioneer species on bare soil
Retains moisture and nutrients in ecosystems
Seed bed for higher plants
Most abundant plant in polar ecosystems
Peat bogs cover 1% of the Earths land surface, area = half the United States !!
Peat bogs are very acidic, pH = 4 or lower, most acidic natural environment
Mosses - Economic Importance
Sphagnum moss is commercially important
>Compressed into peat, used for fuel
>Cotton absorbs 4-6 times its weight in water, but Sphagnum absorbs > 20 times its weight!!
used for diapers
enriching garden soil
dressing wounds in war
Phylum Hepaticophyta Liverworts
9,000 species, Marchantia, PorellaSimplest bodies of any green plant, looks like a flat scaly leaf with prominent lobes
Lobes suggested the shape of a liver, hence hepato - phyta = Greek for liver plant, liver - wort from Anglo Saxon wyrt = herb
During the Middle Ages, because of its resemblance to the human liver, liverworts were used to treat liver diseases
Doctrine of Signatures claimed that the creator has intentionally created plants to look like the parts of the body they could be used to cure!
Mandrake root was a heal-all because it looked like an entire human body
Can you guess what walnuts were used for?
Walnuts were used to treat brain disease!!
Liverworts store food as oil instead of starch, and lack stomata
Life cycle similar to mosses - gametophyte is dominant stage (the leafy green plant)
Archegonia hang from the underside of tiny umbrellas
Sperm swims to the egg, zygote develops into tiny diploid sporophyte that remains attached to the umbrella
Haploid spores are surrounded by elaters, long, twisted, moist cells
When the elaters dry out, they twist and jerk around, scatter the spores
Asexual reproduction by gemmae cups, little cups with tiny liverwort inside, dispersed by drop of water
Phylum Anthocerophyta Hornworts
100 species - AnthocerosGametophytes look like liverworts, but send up a tiny moss-like sporophyte
More closely related to mosses (stomata)
Symbiotic with cyanobacteria Nostoc and Anabaena, which fix nitrogen for the hornwort