Chapter 3 plants

Chapter 3: Plants

Summary

Why are plants important?Evolution4 major groupsLife cycle – generalKey lineages

Why are Plants Important?

3 categories: Ecosystem services Fuels and fibers Other

Evolution

It started with green algae, confined to a watery environment, ~ 570 mya.

Land plants 1st appeared about 450 mya, preceding land animals.

Evolution

Invasion of land presented some of the same problems for plants as it did for animals:

4 Major Groups

Based on similar characteristics and order of evolution. Non-vascular land plants, mosses, liverworts and

hornworts Vascular plants

Seedless vascular plants, club mosses, ferns and horsetails

Gymnosperms have “naked” seeds that protect embryo, conifers, cycads and ginkgos.

Angiosperms have enclosed seeds (fruits) and flowers.

Life Cycle

Alternates between sporophyte (2n) and gametophyte (n) generations.

In early land plants the gametophyte stage predominates, later the sporophyte stage dominates.

Nonvascular Plants (Bryophytes)

Characteristics Gametophytes are photosynthetic, sporophytes are

attached to gametophytes and depend on them for nutrition.

Require water to reproduce Most are small and live in moist, temperate

environments.

Non Vascular Plants

Phylum Hepaticophyta – liverworts

Nonvascular plants

Phylum Anthocerophyta – hornworts Gas Exchange:

Stomata (the rest of the plant kingdom has stomata).

Tiny “broom handles” extending from rhizoids (above ground anchors to substrate).

Phaeocerus leavis

Nonvascular Plants

Phylum Bryophyta – mosses *source of peat Rhizoid = anchor,

supports “leaves” which are 1 cell thick.

Vascular Plants

Major developments Vascular tissues to…

Vessels – vascular tissue modified to provide structure in later species.

2 groups: seedless and seed bearing

Seedless Vascular plants

Characteristics Primitive vascular tissue. Roots *Still dependent on water for transport of sperm to

egg.

Seedless Vascular Plants

Phylum Lycophyta – club mosses Extinct varieties were

tree-like but surviving species are small.

Major source of coal.

Seedless Vascular Plants

Phylum Psilotophyta Whisk ferns: no leaves or

roots, grow on rhizoids or they are epiphytes.

Horsetails: photosynthetic stems, leaves are less prominent than stems in some varieties. Grow well in wet, boggy areas.

Seedless Vascular Plants

Phylum Pteridophyta - ferns Most abundant, closest

relative to seed plants.

Fern sporangia

Seed-bearing Vascular Plants Ch 28

Characteristics Sporophyte stage dominates. Major development is the seed that protects embryo

and allows for a dormant period. 2 types of gametophytes or structures:

Male (pollen-sperm) and Female (ovary – eggs)

Seed-bearing Vascular Plants

2 groups Gymnosperms – “naked” seeds. Ovules (eggs) are

partially exposed on scales; sperm are motile or nonmotile.

Angiosperms – “vessel” seeds (fruit). Ovules are totally enclosed, sperm are motile.

Seed-bearing Vascular Plants

Gymnosperms – 4 phyla Gnetophyta –

Cycadophyta (cycads) –

Ginkgophyta –

Cycad Ginkgo

Seed-bearing Vascular Plants

Gymnosperms – 4 phyla cont’d Coniferophyta (conifers) – largest group; pines, firs,

cedars, yews, cypresses, etc. Produce male and female cones. Pollen grains and ovules develop at the base of scales.

Pollen grains float into female cones and stick on ovules. Female cones take 1-2 seasons to mature and release

their seeds.

Seed-bearing Vascular Plants

Anthophyta (Angiosperms) – Characteristics Flowers and fruits Dominate the plant world

Seed-bearing Vascular Plants

Anthophyta – 6 clades. Basal angiosperms: Amborella, water lilies, star

anise. Core angiosperms:

Magnoliids – magnolias, laurels, etc. Monocots – derived from Magnoliids, 1 cotyledon (seed

leaf), no woody tissue, leaf veins parallel, flower parts are multiples of 3. Lilies, grasses, yucca, irises

Eudicots (true dicots) – 2 cotyledons, leaf veins are web-like, woody tissue, flower parts are multiples of 4-5. Trees, shrubs, annuals.

Angiosperms – what is the purpose of flowers?

Figure 30-23Figure 30-23aFigure 30-23a

“Corpse” flowers smell like rotting flesh and attract carrion flies.