Plant Classification and Adaptations

Plants are classified into phyla; mosses and relatives are seedless nonvascular plants.
Nonvascular plants absorb water and nutrients close to the ground and require free-standing water for reproduction.
Liverworts (Phylum Hepatophyta): often on wet rocks, can be thallose or leafy.
Hornworts (Phylum Anthocerophyta): tropical forests, flat lobed body.
Mosses (Phylum Bryophyta): common seedless nonvascular, e.g., sphagnum moss.
Club mosses & ferns are seedless vascular plants with a vascular system enabling greater height.
Require free-standing water for reproduction.
Club mosses (Phylum Lycophyta): oldest vascular plants, not true mosses.
Ferns (Phylum Pterophyta): whisk ferns and horsetails are close relatives, large leaves called fronds.
Seed plants: cone-bearing and flowering, reproduce via pollination without free-standing water.
Seeds nourish, protect, and disperse plant embryos.

Vascular system: transports water, nutrients, and sugars, enabling growth.
Lignin: hardens cell walls in vascular tissues, providing stiffness.
Pollen grains: reproduction without free-standing water, carried by wind or animals.
Seed: storage for plant embryo, seed coats protect from drying.
Plants evolve with other organisms, sharing mutualistic relationships (e.g., plant roots and fungi, flowering plants and pollinators).
Defensive adaptations: spines, thorns, defensive chemicals.

Land plants evolved from green algae, sharing photosynthetic traits, chlorophyll, starch storage, and cellulose cell walls.
Genetic analysis points to Charophyceae algae as common ancestor; important characteristics originated here.
True plants evolved through natural selection, adapting to land through:
- Cuticle: waxy layer to retain moisture.
- Stomata: tiny holes for air movement.

Agriculture: stable food supplies through farming, artificial selection.
Botany: study of plants.
Ethnobotany: how cultures use plants.
Plants as economic resources: traded for millennia.
Plant compounds in medicine:
- Pharmacology: study of drugs and effects.
- Salicin (aspirin) from willow trees.
- Alkaloids (e.g., taxol) with anti-cancer properties.

Flowering plants (largest phylum) have adaptations for efficient pollination (flowers) and seed dispersal (fruit).
Classification based on seed type:
- Monocots: single cotyledon (seed leaf), parallel veins, flower parts in multiples of 3, scattered vascular bundles.
- Dicots: two seed leaves, netlike veins, flower parts in multiples of 4 or 5, vascular bundles in rings.
Categorization by stem type (woody or herbaceous) and lifespan:
- Annuals: mature, flower, and die in one year.
- Biennials: two-year life cycle.
- Perennials: live more than two years.