Chapter 29 Plant Diversity I: How Plants Colonized Land

Characteristics photoautotrophic mulitcellular eukaryotes cellulose cell walls store carbohydrates as starch chlorophyll a, b, & carotenoids mitosis & meiosis

Plant Evolution

Evolution 400 mya, plants colonized land gametangia – jacketed sex organs evolved and protected gametes, embryos from desiccation heteromorphic alternation of generations sporophyte more conspicuous, except in bryophytes followed changes in terrestrial conditions

Gametangia

Adaptations to land gametangia seeds cuticle stomata vascular tissue (xylem & phloem) lignin – supports cellulose matrix

Major periods in plant evolution 1)terrestrial adaptations allowed plants to move from water (algae) to land ~ 400 mya 2)vascular tissue evolved 3) origin of the seed ~ 260 mya allowed embryos to leave the parent plant encased in a resistant coat with food supply 4) evolution of flower ~ 130 mya (specialized reproductive structure producing ovary- enclosed seeds)

Ancestry evolved from Chlorophyta (green algae), more specifically Charophyceans with chl. a & accessory pigments, cellulose cell walls, store starch, form cell plates in cytokinesis divergence from common ancestry or separate origins from different algae types resulted in vascular & nonvascular (hornworts, liverworts, mosses) plants trend toward increasing dominance of diploid sporophyte in vascular plants

Classification Nonvascular plants: -no true roots, stems, leaves Division Bryophyta – hornworts, liverworts, mosses ~ 16, 000 species - lack many terrestrial adaptations - low-growing, require damp, shady places

Bryophytes

Classification Vascular plants: (Tracheophytes) - true roots, stems, leaves Seedless plants Division Psilophyta – whiskferns ~ 10 – 13 species - ex: Psilotum

Classification Division Lycophyta – club mosses ~ 1,000 species - may be epiphytic – grow on substrates, but are not parasites - have sporophylls – leaves specialized for reproduction - ex: Lycopodium

homosporous – have both M & F sex organs produce a single type of spore heterosporous – 2 types of spores megaspores – develop into female gametophytes microspores – develop into male gametophytes

Classification Division Sphenophyta – horsetails ~ 15 species - ex: Equisetum Division Pterophyta – ferns ~ 12,000 species - microphylls – leaves arising from stem with singular vascular tissue - megaphylls – branched system of veins

Seedless vascular plants

Chapter 30 Plant Diversity II: The Evolution of Seed Plants

Classification Seeded plants Gymnosperms – “naked seed” plants Division Coniferophyta – cone bearers ~ 550 species - leaves are modified as needles - transport water in tracheids – primitive, tapered cells which function in mechanical support - ex: Pinus, sequoia, fir, spruce

Pollen cones

Pine seed

Classification Division Cycadophyta – cycads ~ 100 species - bear naked seeds on scales - ex: sago palm Division Ginkgophyta – ginkgoes - 1 species - resistant to pollution - ex: Ginkgo biloba

Sago palm (cycad)

Classification Division Gnetophyta ~ 70 species ex: Gnetina, Welwitschia

Classification Angiosperms – “flowering plants” ~ 235,000 species Division Anthophyta Class Monocotyledonae – monocots - one cotyledon (embryonic seed leaf) - parallel venation in leaves - vascular bundles scattered in stem - flower parts in 3’s - ex: grasses, lilies * vessel elements, fiber cells

Angiosperms

Flower anatomy

Fruit – mature ovary Seed – mature ovule

Tracheids and vessel elements

Classification Class Dicotyledonae – dicots - 2 cotyledons - branched venation - vascular bundles in a ring - flower parts in 4’s or 5’s *Double fertilization – characteristic of Angiosperms (prevents squandering of nutrients), also evolved independently in some gymnosperms

Pollinators