The Evolution of Plants Kingdom Plantae The Evolution of Plants

Introduction More than 280,000 species of plants inhabit Earth today. They range in size from 1mm across to 100m tall. Land plants (including the sea grasses) evolved from a certain green algae, called charophytes, between 425 million to 490 million years ago. Note: Evidence for this includes: - both having chlorophyll - cell plate formation in mitosis - cell walls made of cellulose - ability to store excess food as starch

Fig. 29.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Characteristics of Plants: Eukaryotic Multicellular Carry out photosynthesis Most are terrestrial Cell walls composed primarily of cellulose Sessile – can’t move from place to place

4 main groups of land plants: Bryophytes – most common are mosses 2) Pteridophytes – includes ferns 3) Gymnosperms – includes pines and other conifers 4) Angiosperms – flowering plants

Plant Life Cycles: All plants have a two-generation life cycle known as ALTERNATION OF GENERATIONS.  A plant exists in 2 forms: 1) Gametophyte Generation - haploid (1N) generation is the gametophyte that produces gametes These gametes fuse to produce a diploid zygote, which grows into a diploid sporophyte plant and then the plant is in the ………………….

Plant Life Cycles cont’d: 2) Sporophyte Generation - diploid (2N) generation is the sporophyte that produces spores by meiosis - plant looks quite different from gametophyte

*spores are haploid structures that develop or mature into the gametophyte plant *usually, lower plants spend their life longer in the haploid (1N) generation

Examples: Mosses, Liverworts, Hornworts, Sphagnum, Peat moss Nonvascular Plants Bryophytes Examples: Mosses, Liverworts, Hornworts, Sphagnum, Peat moss

Bryophytes cont’d Seeds - no (spores) Vascular tissue - no - lack true stems and leaves Flower

Bryophytes cont’d Other Characteristics Simplest plant life, only few centimetres in height Very dependent on water to complete life cycle Sperm must swim from male organ to female organ Must live close to ground to obtain sufficient water Anchored by tubular cells or filaments of cells, called rhizoids

Seedless Vascular Plants Pteridophytes Examples: Ferns, Horsetails and Club mosses (Lycophytes)

Pteridophytes cont’d Seeds - no (spores) Vascular tissue - yes (roots, stems and leaves) - able to grow to great heights - 2 types: 1) xylem 2) phloem Flower - no

Pteridophytes cont’d Other Characteristics Moisture needed for fertilization Male gamete needs to swim to female on gametophyte Developed symbiotic mycorrhizal relationships (between roots and fungi) that help them obtain water and other nutrients from soil

Plant Evolution The evolution of plants is highlighted by two important landmarks: (1) the evolution of seeds, which lead to the gymnosperms and angiosperms, the plants that dominate most modern landscapes (2) the emergence of the importance of seed plants to animals, specifically to humans. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Agriculture, the cultivation and harvest of plants (primarily seed plants), began approximately 10,000 years ago in Asia, Europe, and the Americas. This was the single most important cultural change in the history of humanity, for it made possible the transition from hunter-gather societies to permanent settlements. The seeds and other adaptations of gymnosperms and angiosperms enhanced the ability of plants to survive and reproduce in diverse terrestrial environments. Plants became the main producers on land. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Examples: Coniferous trees like Pine, Spruce and Cedars Gymnosperms The First Seed Plants Examples: Coniferous trees like Pine, Spruce and Cedars

Gymnosperms cont’d Seeds - yes (naked) Vascular tissue - yes Flower

Gymnosperms cont’d Other Characteristics Dominant land plants Naked seed in cones (not enclosed by fruit) Haploid male pollen fertilizes ovules in female cone producing diploid zygote/embryo Zygotes grow in seeds on surface of female cone scales, falls on soil and develops into plant Mycorrhizal relationships with symbiotic fungi

Angiosperms Flowering Plants

Angiosperms cont’d Seeds - yes (enclosed by fruit) Vascular tissue Flower

Angiosperms cont’d Other Characteristics Seeds mean less dependent on water Seed enclosed in an ovary, which becomes fruit to protect and nourish Main function of fruit is to help disperse seeds Flowers perform same function as cones in gymnosperms – produce pollen and egg Flowers are diverse, specialized for the way the plant is pollinated