BSC 116 Lecture Notes - Lecture 6: Non-Vascular Plant, Vascular Plant, Gametophore

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Evolution and Diversity of Plants:
Five key events in the history of plant evolution:
o Multicellularity
o 475 My, invasion of land
o 420 My, evolution of vascular tissue
o 30 My, appearance of (extant) seed plants
o 140 My, evolution of flowers
Grades of plant morphology:
o Non-vascular bryophytes
o Vascular plants
o Seed plants
o Angiosperms (flowering)
Vascular tissue- specialized cells that transport water, nutrients, etc.
Bryophytes- non-vascular plants
o Three groups:
Hepatophyta (liverworts)
Anthocerophyta (hornworts)
Bryophyta (mosses)
Most diverse and most commonly encountered
o Typically form low "carpets" rather than upright branches
o Bryophyte life cycles dominated by a gametophyte, but with prominent sporophyte
Plant life cycles are characterized by alternation of generations
o Alternation of generations- alternating, multicellular haploid (n) and diploid (2n) phases
Sporophytes (2n) produce spores (n) by meiosis
Spores (n) develop into gametophytes (n)
Gametophytes (n) produce gametes (n) by mitosis
Gametes (n) fuse to produce sporophytes (2n)
o Dominant phases vary among plant groups
Bryophyte life cycle dominated by gametophyte stage
Gametophytes (n) develop from spores (n)
Spores germinate to form branched protonemata (1 cell thick)
Each protonemata produces 1+ gametophore(s)
Anchored by rhizoids; not roots
Gametophytes (n) have either female or male gametangia
Archegonia- produce eggs
Antheridia- produce flagellated sperm
Sperm must swim through water to fertilize eggs
Limits mosses to moist habitats
Bryophyte sporophytes are dependent on parental gametophytes
Sporophytes (2n) grow from embryos in archegonia
Green when young, but get nutrition from parental gametophyte
Sporangium (=capsule) on a stalk
Opens via peristome
Releases spores gradually: spread by wind
Their life cycles and lack of vascular tissue limit the diversity of bryophytes
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