Increasing dominance of sporophyte in the alternation of generations

Advent of the seed - replaced the spore as the main means of dispersing offspring

Evolution of pollen - became the vehicle for sperm cells in seed plants

In the nonvascular plants - gametophyte was dominant stage - sporophyte dependent on gametophyte for protection and nourishment

In the seedless vascular plants - sporophyte became dominant stage - gametophyte inconspicuous and free-living (not dependent)

In the seed plants - sporophyte dominant stage - gametophyte enclosed within tissues of sporophyte, from which it obtains its nourishment

Consists of components representing 3 plant generations:

Microspores (within microsporangia) develop into haploid pollen grains - male gametophyte

Protected by tough coats containing sporopollenin

In vicinity of ovule, will elongate a pollen tube and discharge sperm into female gametophyte tissue

In most cases, lacks flagella - very different dispersal compared to lower plants, which must swim through film of water to fertilize egg(s)

Cycadophyta - cycads - commonly known as sago palms

Ginkophyta - ginkgo is only extant species - deciduous

Gnetophyta - 3 genera (not closely related) - appear to be most closely related to angiosperms

Coniferophyta - conifers - largest group of gynmosperms - includes pines, firs, junipers - largest and oldest organisms on earth (e.g., sequoias and bristlecone pine (4,600 years old)

Most diverse and geographically widespread of all plants - 250,000 known species (compared to 720 gymnosperm species)

Adaptations included refinements in vascular tissue (vessel elements evolved from tracheids in gymnosperms) and the flower (reproductive structure) - the defining reproductive structure in angiosperms

Class Monocotyledones - monocots - one leaf (cotyledon) on embryo; veins parallel - includes grasses, palms, yuccas

Class Dicotyledones - dicots - two cotyledons on embryo; veins branched - includes most broad-leaf angiosperms (e.g., roses, peas, oaks, maples)

Reproductive structure - consists of 4 whorls of modified leaves:

Generally only one fertilized egg develops

Seeds "naked" - wind primary means of dispersing pollen

Seeds dispersed primarily by wind & water

Double fertilization - one fertilized eggs - triploid endosperm (nutrients for embryo)

Seeds within ovary

Fruit - mature ovary - attractive to animals - important dispersal mechanism

Appearance and proliferation of plants reduced CO₂ levels in atmosphere - resulted in global cooling (minimized "greenhouse effect")

Plants and animals have influenced each others evolutionary adaptations - coevolution

Foundation of food webs

Natural resources - lumber (primarily gymnosperms) & agriculture (almost entirely angiosperms) - many pharmaceutical drugs