PLANT DIVERSITYChapters 29 & 30

Definition of Plants

• Multicellular• Eukaryotic• Photosynthetic• Autotrophic• Cell walls made of cellulose• Chlorophylls a and b

Plant Evolution

4 Main Groups of Land Plants• Bryophytes – non vascular plants

• Mosses, liverworts, hornworts

• Pteridophytes - seedless vascular plants• Lycophytes, ferns, horsetails, whisk ferns

• Gymnosperms – naked seed plants• Ginko, cycads, gnete, conifers

• Angiosperms – flowering plants

Land Plant Evolution

• Ancestral green algae

• Aquatic plants: Charophyceans

• Land plants:• Development of vascular tissue• Development of seeds• Development of flowering plants

Charophyceans

• Closest relative of land plants

• Algal group

• Similarities with land plants• Rosette cellulose-synthesizing

complexes• Located in plasma membranes

• Peroxisomes• Flagellated sperm (some land

plants)

Evidence of common ancestor with charophycean algae

• Homologous chloroplast• Homologous cellulose walls• Homologous peroxisomes• Homologous sperm• Molecular systematics

• Chloroplast DNA• Ribosomal RNA

Adaptations of Land Plants• Apical meristems

• Roots and shoots – growth• Multicellular, dependent embryos

• “embryophytes”• Transfer of nutrients from parent

• Alternation of generations• Sporophyte (diploid) and gametophyte (haploid)

• Gametangia – gametes are produced within multicellular organ• Female – archegonia• Male - Antheridia

• Walled spores – resist drying out• Cuticle – waxy covering, water conservation• Stomata – pores, water conservation• Vascular tissue – transport water and minerals

Apical meristems of plant shoots and roots

Embryos of Land Plants

Alternation of generations

Walled Spore

Gametangia: Gametes produced within multicellular gametangia

Archegonium - female Antheridium - male

egg sperm

Cuticle of a stem: Prevents drying out

Vascular Tissue: Xylem and Phloem

Xylem(water)

Phloem(food)

Development of Alternation of Generations

• Delay in meiosis until one or more mitotic divisions of the zygote occurred

• Result: multicellular, diploid sporophyte• Increases number of spores produced per zygote

What is the Plant Kingdom?

Bryophytes

• Three phyla• Hepatophyta: liverworts• Anthocerophyta: hornworts• Bryophyta: mosses

• Non-vascular• Earliest land plants• Gametophyte (haploid) is dominant form• Anchored by rhizoids• No true roots or leaves

Bryophytes

Life cycle of a moss

Moss life cycle

gametophyte gametangia sporophyte

sporophyte sporesProtonemata

(pre-gametophyte)

Sphagnum, or peat moss

gametophyte sporophyte

Vascular Plants• Vascular plants have

• Xylem – transports water• Phloem – transports food• Dominant sporophyte generation

• First vascular plants were seedless

• Three Groups• Seedless plants• Gymnosperms• Angiosperms

Seedless Vascular Plants

• Two phyla• Lycophyta – lycophytes• Pterophyta – ferns, whisk ferns, horsetails

• Most have true roots and leaves

• Still require water for fertilization

Pteridophytes

Club “moss” Whisk fern

Horsetail Fern

Hypothesis for the development of leaves

• Probably evolved from a flap of stem tissue• Stem had vascular tissue• Microphylls

• Macrophylls – larger leaves with branched veins

Ferns

Life cycle of a fern

Fern sporophyll, a leaf specialized for spore production & sori

Sorus (sori): Clusters of sporangia – found on underside of leaves

Mature fern sporangium – releasing spores

Fern gametophyte

Archegonia of fern

zygote

Flagellated sperm from antheridium fertilize eggs in archegonium

Fern sporophytes

Evolution of Seed Plants

• Reduction of gametophyte continued

• Seeds – important means of dispersal

• Pollen – eliminated water requirement for fertilization• Pollination

• Two clades• Gymnosperms• Angiosperms

Gametophyte/ Sporophyte Relationships• Seed plants: further reduced gametophyte• Female gametophyte and embryo protected by

parental sporophyte

Seed Development

• Fertilization initiates the transformation from ovule to seed• Sporophyte embryo• Food supply• Protective coat

Seed Dispersal

• Seeds have adaptations for dispersal

• Wind• Water• Animal

Gymnosperms

• Four phyla• Ginko• Cycads• Gnetophytes• Conifers

• Naked seed – no fruit (ovary)• Seeds develop on surface of sporophylls• Evolved before angiosperms

Phylum Coniferophyta

Douglas fir Sequoia

Phylum Coniferophyta: Frasier Fir

Characteristics of Conifers• Cone: reproductive structure

• Cluster of sporophylls• Female cones: produce ovules - “pine cones”• Male cones: produce pollen

• Seed develops from fertilized ovule – scale of cone

• Dominate in areas with short growing season• High latitude or altitude

• Most are evergreens

• Some have needle-shaped leaves• Adapted for dry conditions• Thick cuticle

Life cycle of a pine

Pollen cone (male) – produces pollen

Pine pollen

Pine embryo

Embryo(new sporophyte)

Angiosperms: Flowering PlantsMajor Clades:

Phylum Anthophyta: Angiosperms

• Vascular seed plants• Reproductive structures: flowers, fruits• Most diverse group of plants today• 2 groups

Monocots Dicots

# Petals Multiples of 3 Multiples of 4 or 5

# Cotyledons 1 2

Vascular bundles Scattered Circle

Root Fibrous Tap root

Xylem cells in Angiosperms

• Trachids• Support• Water transport

• Fiber **• Support

• Vessel element **• More efficient

** Evolutionary adaptations of angiosperms

Flower Structure: Reproductive Adaptation of Angiosperms

Life cycle of an angiosperm

Fruit and Seed Dispersal

Flower-pollinator relationships