Post on 18-Dec-2015
transcript
Non-Vascular Plants
Evolution of Land Plants
• Land plants evolved from green algae
• The green algae called charophyceans are the closest relatives of land plants
• Comparisons of both nuclear and chloroplast genes– Point to charophyceans
as the closest living relatives of land plants
Chara, a pond organism
(a)10 mm
Coleochaete orbicularis, a disk-shaped charophycean (LM)
(b) 40 µm
Origin and Diversification of Plants
• Fossil evidence indicates that plants were on land at least 475 million years ago
• Whatever the age of the first land plants those ancestral species gave rise to a vast diversity of modern plants
Plant Evolution
Bryophytes(nonvascular plants) Seedless vascular plants Seed plants
Vascular plants
Land plants
Origin of seed plants(about 360 mya)
Origin of vascular plants (about 420 mya)
Origin of land plants(about 475 mya)
Ancestralgreen alga
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Bryophytes
• Life cycles of mosses and other bryophytes are dominated by the gametophyte stage
• Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants– Liverworts, phylum Hepatophyta– Hornworts, phylum Anthocerophyta– Mosses, phylum Bryophyta
Bryophytes
• Nonvascular (pass water cell-to-cell)
• Seedless (reproduce by spores)• Low growing• Phylum Bryophyta (also includes
liverworts & hornworts)• Grow on moist brick walls, in
sidewalks, as thick mats on forest floors, and on the shaded side of trees
Bryophytes
• Can survive periodic dry spells, reviving when water becomes available
• Require water for fertilization so sperm can swim to egg
• Rhizoids (root like structures) anchor mosses
• Have waxy covering called cuticle on aerial parts to prevent desiccation
• Dominant form of a moss is a clump of leafy green gametophytes (photosynthetic)
• Moss alternates between a haploid (1n) gametophyte and diploid (2n) sporophyte
• Gametophyte generation produces gametes (eggs & Sperm)
• Sporophyte generation forms at the top of the gametophytes and produces spores
• Stalk-like sporophytes lack chlorophyll
• Capsule at the top of the sporophyte forms haploid (1n) spores
a Diploid (2n) sporophyte stage (contains two sets of chromosomes, one from male and one from female) and a
Haploid (1n) gametophyte stage (contains one set of chromosomes)
This type of life cycle is called Alternation of Generations
• Sexual reproduction in Moss:
• Moss produce 2 kinds of jacketed gametes --- eggs & sperm• Egg producing organ is called the archegonium• Eggs are larger and nonmotile• Sperm producing organ is called the antheridium• Sperm are smaller, flagellated cells• Antheridia & archegonia are both part of the gametophyte
plant• Fertilization can occur only during or soon after RAIN when
the gametophyte is covered with Water• Sperm swim to the egg by following a trail of
chemicals released by the egg in the water• Fertilization produces a zygote that becomes a sporophyte• Mature sporophytes produce homosporous spores (all the
same type)• Mature capsules open & release spores spread by wind• Spores landing on moist places germinate
into protonema that become new gametophytes
Only the zygote is 2n
Liverworts
• Have no true roots or shoots
• Non- vascular• Require water to
reproduce• Have no or very
little leaf structure• Cannot live in
sporophyte form
Hornworts
• Free-floating aquatic plant, or land plant
• No vascular tissue• No true leaves or
roots• Can live in both
gametophyte and sporophyte forms
Mosses
• Land plant
• Most have no vascular tissue
• Majority of life spent in gametophyte stage
• Need water to breed
• No leaves or roots
• Sporophytes are capsules on stalks