Chapter 30: Plant Evolution and Classification 30-1 Overview of Plants 30-2 Nonvascular Plants 30-3 Vascular Plants

Revisiting Evolution The first true plant is thought to have been similar to a green alga, with adaptations that enabled it to survive the dry conditions on land. Assessing Prior Knowledge Explain how successive generations become adapted to different conditions and evolve into different species. Describe what types of data are used to construct a phylogenetic tree.

I. Adapting to Land (from green algae?) Terrestrial life evolved ~ 430 m.y.a. (following ozone) and at one point small, club-shaped plants began to grow in the mud at water’s edge Overview of Plants Like green algae, plants possess chlorophyll, store energy as starch, and have cellulose making up their cell walls.

(A) Preventing Water Loss Benefits of migrating? More exposure to sunlight, increased CO 2 levels, and greater supply of nutrients. (1) Cuticle (an early adaptation to life on land) A waxy protective covering on plant surfaces that prevents water loss (balanced out by stomata to exchange gases through cuticle)

(B) Reproducing by Spores and Seeds Evolved to aid terrestrial plant reproductive cells from drying out. (1) Spore (widespread & water-resistant—primitive dispersal strategy) Haploid reproductive single cell surrounded by a hard outer wall. (2) Seed (more evolved dispersal strategy and is multicellular) Embryo surrounded by a protective coat and contains an endosperm. (3) Endosperm Tissue that provides nourishment for the developing plant embryo.

(C) Transporting Material throughout the Plant As a multicellular organism, differentiated plant cells need to share resources to grow, divide, and carry out metabolic activity. (1) Vascular Tissue (2 types: more evolved terrestrial plant species) Specialized plant tissue that transports water and dissolved substances. (2) Xylem Vascular tissue carrying water and inorganic nutrients in one direction, from the roots to the stems and leaves. (3) Phloem Vascular tissue carrying organic compounds (carbohydrates), and some inorganic nutrients in ANY direction, depending on the plant’s needs.

(4) Woody Tissue (advantage in growing to greater heights, more sunlight) Formed from several layers of xylem, usually concentrated in the center of the stem (generally brown and rigid) (5) Herbaceous Tissue (shorter plants, non-woody plants) Vascular tissue that is NOT surrounded by schlerenchyma cells, making the stems of herbaceous plants soft, green, and flexible.

II. Classifying Plants Kingdom Plantae is divided into 12 phyla (a.k.a. divisions) divided into 3 groups based upon the presence of vascular tissue. (1) Nonvascular Plants (3 phyla, less diversified, no xylem or phloem) More primitive plants that lack true vascular tissue, roots, stems, and leaves. (2) Vascular Plants (9 phyla, more diversified) More recently evolved plants that possess vascular tissue, roots, stems, and leaves.

Non-Vascular Plants Mosses10,000 Liverworts6,500 Hornworts100 Vascular Plants - Seedless Whisk ferns Club-mosses1,000 Horsetails15 Ferns12,000 Seed Plants - Gymnosperms Conifers550 Cycads100 Gingko1 Gnetae70 Angiosperms Flowering plants235,000

(3) Seed-Bearing Plants More evolved than seedless plants (spore-bearing plants), include four phyla of gymnosperms and one phylum of angiosperms. (4) Gymnosperms (non-flowering plants) Class of seed-bearing plants that produce seeds that are NOT enclosed in fruits (e.g., pine trees) (5) Angiosperms (flowering plants) Class of seed-bearing plants that produce seeds within a protective fruit (e.g., apple and orange trees)

(B) Alternating Life Cycles All plants maintain a life cycle that involves TWO phases, named after the type of reproductive cells the plant produces in each phase. (1) Sporophyte (diploid plant—2N, pine & oak trees are large sporophytes) Plant producing spores, known as the sporophyte generation/phase and is the dominant phase in VASCULAR plants. (2) Gametophyte (haploid plant—1N) Plant producing gametes (egg and sperm cells), known as the gametophyte generation/phase and is the dominant phase in NONVASCULAR plants.

(3) Alternation of Generations (NOT found with green algae) A type of life cycle which alternates between the sporophyte and gametoyphyte phases. NOTE: The gametophyte makes gametes, which combine to make a diploid zygote, of which divides to form a sporophyte plant (2N). Sporophyte (through meiosis) produces haploid spores (1N)—these spores are released by most seedless plants BUT are retained by seed-bearing plants. The life cycle begins again when spores divide by mitosis to form new gametophytes.

I. Seedless Vascular Plants Four phyla (fern allies and ferns), dominated the Earth until about 200 m.y.a. relying upon spores as the mobile sexual reproductive cells Vascular Plants

(1) Rhizome (“horizontal root”) Fibrous stem that grows horizontally underground (2) Fiddleheads Tightly coiled new (immature) leaves of ferns (3) Fronds Mature leaves that develop sori (pl. of sorus) on the underside where haploid spores develop.

II. Vascular Seed-Bearing Plants The mobile sexual reproductive part of seed plants is the multicellular seed, an evolutionary success story of adaptation and germination. (1) Germination Abiotic conditions favor growth, a seed sprouts as the embryo begins to divide and grow into a new seedling. (2) Seedling New young plant that has emerged as an embryo through the seed coat. (3) Cone (found among the 4 phyla of gymnosperms) Reproductive structure made of hard scales, bearing the seeds on the open surface. (serve similar roles in gymnosperms as flowers do for angiosperms)

(G) Monocots and Dicots (all angiosperms are divided into two classes) Flowering plants are classified based upon the number of cotyledons present in the plant embryo, as well as a few other features. (1) Cotyledons Seed leaves found in in the plant embryo, either one (monocot) or two (dicot) leaves are present. (NOTE: By comparison, gymnosperms typically have two or more cotyledons) (2) Parallel Venation (monocot leaves) Most mature monocot leaves have several main veins or bundles of vascular tissue running roughly parallel to each other. (3) Net Venation (dicot leaves) Most dicots have one or more non-parallel main veins that branch repeatedly, forming an interconnected network.