The Evolution of Land Plants 1 Colonization of

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