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BI-125 Botany
Bryophyta
Mosses & Liverworts
General characteristics
- gametophyte dominant life cycle
- non-vascular
- some have water conducting hydroid cells in center of stem
and food-conducting leptoid cells surrounding hydroids
- some [Sphagnopsida] have closely appressed descending branches
that function by wick action as water-conducting structures
- Sphagnopsida can lift water approximately 18 cm above water surface
(LaFrance, 1970. unpubl.)
- male gametes flagellated; swim through dew to female gametangia
- female gametes remain in gametangium, even after fertilization
- sporophytes grow attached to gametangium
- germinating spores produce protonema
then typical gametophytes
- diploid zygotes grown on petri dishes can become gametophytes rather than sporophytes
produce diploid gametes, and quadraploid zygotes
up to 32n gametophytes.
- haploid spores grown in 3-d matrix sometimes resemble sporophytes
with abortive spore formation
Classification
- Hepaticophyta (liverworts)
- thalloid liverworts
- leafy liverworts
- protonema filamentous if present
- gametophyte exhibits prostrate growth
- thalloid gametophytes, a flattened leaf-like thallus
dichotemous branching
1-celled rhizoids on lower surface
asexual reproduction by spore-like gemmae
- leafy gametophytes, a stem-like axis with 2 rows of leaf-like thalli
unequal branching
few 1-celled rhizoids on axis
asexual reproduction by terminal decay
- Anthocerophyta (hornworts)
- gametophyte, a filmy thallus less than 2 cm diameter
- sporophyte, an erect, thin (less than 0.5 cm), greenish, curved rod up to 5 cm tall
central columella (believed to be conducting, hydroid?)
- Bryophyta (true mosses)
- gametophyte with branched stem [branches are leaf-like]
- leaves are almost microscopic, 1-cell thick, triangular shaped
- male and female gametangia on separate branches or separate plants
- male gametes [2- or 4-flagellae] swim through dew
to female eggs in gametangia, typically apical
- Sporophyte usually colorless, golf tee shaped structure attached to gametophyte
- top (lid) of sporophyte opens explosively, releasing spores
- protonema typically resembles branched filamentous algae
- asexual reproduction by terminal decay produces clumps of clones of the parent
- small fragments of gametophytes may be also serve for asexual reproduction
by forming protonema, then new gametophytes.
- orders of Bryophyta:
- Bryales (true moss)
- Sphagnales (peat moss)
fossil history
The non-woody Bryophyta fossilize poorly, so the fossil record is scant.
- oldest known thallose liverwort = Pallavicinites devonicus, Metzgeriales
Devonian, biostratigraphic date: 350 Myr BP; USA
- oldest known true moss = Muscites plumatus, Bryales
Carboniferous, 350-270 Myr BP; England
- oldest known [putative] peat moss = [species not stated], Protosphagnales
Permian, 270-220 Myr BP; [location not stated]
- data from J.-P. Frahm 1994. Moose-lebende Fossilien,
Biologie in unseren Zeit vol. 24, pp. 120-124.
English translation in Botanical Electronic News vol. 168 (July 5, 1997)
[www.ou.edu/cas/botany-micro/ben/]
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