Plant Evolution Plants evolved about 475 million years ago from charophytes (a group of green algae)...
-
date post
20-Dec-2015 -
Category
Documents
-
view
223 -
download
0
Transcript of Plant Evolution Plants evolved about 475 million years ago from charophytes (a group of green algae)...
Plant Evolution• Plants evolved
about 475 million years ago from charophytes (a group of green algae) – Most modern
plants are photoautotrophs on land
Plant Adaptations to Land • Most groups are
adapted to dry and often cold habitats through structural modifications– Stomata across
epidermal surfaces– Waterproof cuticle– Lignin-reinforced
tissues– Xylem and phloem
(vascular tissues)
Alternation of Generations
• Land plants alternate between gametophyte (haploid) and sporophyte (diploid) generations
What are bryophytes?
• Mosses, liverworts, and hornworts– Nonvascular (no xylem or
phloem)– Rhizoids store moisture,
anchor gametophyte • Sperm swim through water
droplets or film of water to eggs • Sporophytes stay attached to
larger gametophytes • Spores that give rise to
gametophytes are wind-dispersed
What are seedless vascular plants?
• Lycophytes, horsetails, whisk ferns, true ferns• Dominated by the sporophyte • Spore-bearing structures
– Strobili of horsetails– Sori of ferns
• Sperm swim through water to reach eggs
Gymnosperms: Naked Seeds
• Conifers, cycads, ginkgos, and gnetophytes– Many are well
adapted to dry climates
• Life cycle: No ovaries– Ovules form on
exposed surfaces of strobili or (in conifers) female cones
Angiosperms: Flowering Plants
• Only angiosperms have flowers– Many coevolved with
birds, bees, bats, and other animal pollinators
• Most widely distributed and diverse plant group– Two largest classes:
Eudicots and monocots– Magnoliids preceded
eudicots and monocots
Life Cycle: Flowering Plants • Monocot life cycle: An
example of sexual reproduction in flowering plants– Formation of pollen and
eggs• Double fertilization
produces an embryo sporophyte and nutritive tissue that supports it– Protective seeds form in
ovaries– Outer ovary tissues
later develop into fruits