Plant Diversity

Chapters 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

• 3 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

• 3 Groups– Seedless plants– Gymnosperms– Angiosperms

Seedless Vascular Plants

• 2 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

What is a seed?

• Sporophyte embryo

• Food supply

• Protective coat

• May remain dormant for years

• May be carried by wind, water or animals

Seed Dispersal

• Seeds have adaptations for dispersal

• Wind• Water• Animal

Gymnosperms

• 4 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 Plants

Major 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