the phylogeny of land plants the likely ancestor are charophycean algae chloroplast dna and...

The phylogeny of land plantsThe likely ancestor are charophycean algae

Chloroplast DNA and ribosomal RNA indicate charophycean algae and land plants had common ancestorMembranes of land plants and charophyceans have rosette-shaped arrays of proteins that make the cell walls

• Other algae have linear arrays

Land plants and charophyceans have anti-photorespiration enzymes packaged into organelles called peroxisomes

• Peroxisomes not found in other algae

Similarity of sperm of land plants and charophycean algae

Chara

Land plant life cycle

Gametophyte (1N)

Eggs or sperm

Sporophyte (2N)

Spores (1N)

Major evolutionary events in land plant evolution

1) Invasion of land

Bryophyta

Lack true roots, stems and leavesInstead have rhizoids, caulalia and phyllodes

Require moisture for fertilization

Without vascular tissue; rely on diffusion

Dispersal by spores

Gametophyte is dominant stage

Lack cuticle

Bryophyta (moss)

Bryophyta (hornwort)

Bryophyta (liverworts)

Major evolutionary events in land plant evolution

2) The evolution of vascular tissueXylem for conduction of water

Phloem for conduction of carbohydrates from leaves or fronds to other parts of plant body

3) Sporophyte is dominant phase of life cycle

4) Cutin lines external surfaces

Vascular plants

Roots, stems and leaves present

Presence of vascular tissue

Lycophyta (club mosses)

Lycophyta - club mosses

Do not produce seeds

Spores borne on strobili

Pterophyta (ferns)

Pteridophyta - ferns

Do not produce seeds

Spores produced in sori on the underside of fertile fronds

Major evolutionary events in land plant evolution

5) evolution of seedsA seed is a structure that encloses and protects a developing embryo

6) evolution of pollination

Seed plants

Gametophyte much reduced and dependent on sporophyteSeed consists of sporophyte embryo packaged along with a food supply within a protective coatAdapted for terrestrial existencePollination replaces swimming as the mechanism for delivering sperm to the egg

GymnospermsNaked seedsLack the enclosed chambers (ovaries) in which angiosperm ovules and seeds develop

Rather, gymnosperm ovules and seeds develop on the surfaces of specialized leaves called sporophylls

Wind pollinationWater not needed for pollination

All are woody plants (no herbaceous species)Date from 350 mybp

Ginkgophyta

Only one species

Tree with fan-shaped leaves

Ovules develop into yellow, cherry-like seeds

Ginkophyta

Cycadophyta

Stem unbranched with terminal palm-like leaves

Cone-like sporophylls

Cycadophyta (cycads)

Gnetophyta

Flower-like cones

Xylem composed of tracheids and vessel elements

Pits

Figure 28.4a

Tracheids

Perforatedend walls

Figure 28.4b

Vessels

Gnetophyta (Ephedra or Mormon Tea)

Shrub of American deserts

Gnetophyta (Welwitschia)

Welwitschia

Found in the Nabib Desert

Two enormous leaves,the longest lived of any plant

Grow about five inches a year

Each leaf can reach several hundred square feet in size

Coniferophyta

Sporophylls modified into cones

Wind-pollinated

Xylem with tracheids but no vessels

Coniferophyta

Coniferophyta

Major evolutionary events in land plant evolution

7) Evolution of flowers and fruits

Anthophyta - flowering plants

Reproductive organs within a flower

Gametophytes greatly reduced

Ovules embedded within sporophyte tissue (ovary)

Seeds within a fruit

Appeared in early Cretaceous

Most pollination by insects and birds

The origin of the angiosperms

Darwin wrote about “the abominable mystery” of what the first flowering plant looked like

Angiosperms appear suddenly in the fossil record with no obvious ancestors for a period of 80-90 million years before their appearance

Two hypothesesMagnolia hypothesis

• First angiosperm was a tree with complex flowers

Paleoherb hypothesis• First angionsperm was a non-woody plant with simple flowers

Amborella

Analysis of DNA reveals this genus is the most primitive flowering plant

Flowers with moderate number of petals

Flowers are imperfect (separate male and female gametophytes)

Found only on island of New Caledonia in the South Pacific

Amborella

New Caledonia

Amborella

Water lilies

Monocots

Monocots - parallel venation

Dicots

Dicots - reticulate venation

Diversity of various phyla of land plants

Bryophyta - 18,600 species

Lycophyta - 1,000 species

Pterophyta - 12,000 species

Ginkophyta - 1 species

Cycadophyta - 100 species

Gnetophyta - 70 species

Coniferophyta - 550 species

Anthophyta - 250,000 species!!