The Evolution of Land Plants 1: Colonization of Land 2: Evolution of Seed Plants

Colonization of Land Overview: Plants appeared on land about 475 mya, as the descendants of green algae = charophytes The phylogeny of the Plant Kingdom reflects increasing adaptation to terrestrial habitats The colonization of land by plants changed the biosphere and created adaptive zones that paved the way for other organisms

Adaptations to Life on Land Plant characteristics Embryophytes - new mode of reproduction that solves two problems Alternation of generations - review

Plant Characteristics multicellular, eukaryotic, photosynthetic autotrophs cell walls of cellulose surplus carbohydrates stored as a starch chloroplasts contain chlorophyll a and b stomata secondary products: cuticle; lignin; sporopollenin

Diversity of Modern Plants Highlights of plant phylogeny Classification of plants

Origin of Plants Evolution from charophytes Delayed meiosis and the evolution of alternation of generations

Nonvascular Plants Evolution of embryophytes Gametophyte-dominant life cycle Mosses (Bryophyta)

3 major challenges to life on land water conservation: thick waxy coating on plant surface = cuticle internal system of tubes and vessels = vascular tissue reproduction: spore production and alternation of generations gametophyte: haploid form; produces gametes sporophyte: diploid form; produces spores absorption of nutrients and minerals: symbiotic relationship w/ fungi called mycorrhizae

Nonvascular Plants characteristics transport materials by osmosis and diffusion have flagellated sperm anchored by root-like structures = rhizoids due to first two, these plants need lots of water gametophyte is the dominant form Mosses = most common and well-known nonvascular plants pioneer plants - grow in inhospitable places

Evolution of Vascular Plants have tissues which are able to transport water and nutrients over great distances which allows for greater size and complexity vascular seedless plants: club mosses, horsetails and ferns these plants have the sporophyte as the dominant form: spores develop on the underside of fronds gametophyte forms sex cells; dependent on water for fertilization

Seed Plants vascular plants with seeds: very successful, water is not needed for sustained growth seed = specialized structure that develops from the fertilized egg. Provides 2 advantages: enables embryos to survive in dry/harsh climates provide protection to embryo - physical protection cotyledon = leaflike structures found on a plant embryo which store food and help absorb nutrients from the seed

Two Types of Seed Plants: gymnosperms . . . gymnosperms = “naked seeds”; plants with naked ovules. Most have seeds in the form of cones. Pine, spruce, fir, and gingko 2 types of cones: seed and pollen cones pollen cone = produce male gametophytes - pollen grains seed cone = female gametophyte containing egg cells - ovule Pollination and Germination

. . . and angiosperms angiosperms = “flowering plants”; ensure gamete exchange during reproduction. Produce embryos contained within seeds that are usually inside a fruit