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Chapter 29: Plant Diversity I: How Plants Colonized Land. Overview of Plant Phylogeny. Chamber-contained seed. Chara, the outlier to the plant phylogeny, is a green alga. Naked seed. More Detail. Don’t worry about dates. Nonvascular Plants.
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Overview of Plant Phylogeny Chamber-contained seed Chara, the outlier to the plant phylogeny, is a green alga Naked seed
More Detail Don’t worry about dates
Nonvascular Plants Nonvascular plants also lack woody tissue, seeds, flowers, and fruits Note majority are mosses
Seedless plants also lack flowers and fruits Vascular Plants Not all seed plants have flowers and fruits
Similarities in peroxisomes, flagellated sperm, and cell division also link charophyscean algae with green plants. Cellulose-Synthesis “These distinctly rose-shaped arrays of proteins are found only in land plants and charophycean algae, suggesting their close kinship.” p. 574, Campbell & Reece (2005)
The ancestor of all plants was a green alga • Green algae have plant-like chloroplasts, plant-like cell walls, and a plant-like energy storage molecule (starch)… etc. • The ancestor of plants probably was a green alga that lived whole or partially in very shallow water, perhaps susceptible to periodic drying up • Those algae that could continue to metabolize despite not being completely covered with water presumably possessed a selective advantage—including shading those algae restricted to water • The first roots were stems (stipes) that physically connected out-of-water portions of algae with still-in-water portions • Water diffused through short stems to keep above-water, actively photosynthesizing tissues from desiccating Scenario for Algae to Plants
Algae: • Get minerals and water from surrounding water • Have their bodies supported by surrounding water • Their sperm and spores swim through the water • Plants: • Get their Minerals and Water from soil • Soil is subject to desiccation • Soil also is opaque to sunlight • Do not have their weight supported by surrounding water • Do not have, or have less water for sperm and spores to swim through • To survive on land, plant ancestors had to address these challenges The Challenges of Land
Waxy cuticles: water proofing of plant body • Stomata: holes in waxy cuticle • Sporophyte (alternation of generations): increased productivity per fertilization (does not exist in Charophycean algae) • Vascular tissue: connects roots to leaves • Woody tissue: allows greater plant height • Sporopollenin: polymer which prevents zygotes from drying out • Pollen: non-motile sperm carrier; also male gametophyte • Seeds: “…embryo packaged with a supply of nutrients inside a protective coat.” p. 579, Campbell & Reece (2005) • Flowers: allows more efficient pollen transfer • Fruit: embryo protection and dissemination Plant Innovations
Waxy Cuticle & Water Proofing Air is desiccating (unless humidity is 100%)
Sporophytes, Dominance Note: Plants are heteromorphic
Water and minerals are passed up the xylem, ultimately to be transpired out of the plant Vasculature (etc.) Sugar, amino acids, and other organic molecules are passed down phloem to the stem and roots
Cellulose Cell Walls The cellulose of cell walls is important for supporting plant tissues against gravity’s pull
Lignin is the polymer that gives woody plants their woodiness Lignin Woody Tissue Vasculature allong with woody tissue allowed plants to grow taller, so as to avoid being shaded by other plants
Gametangia Antheridium Oogonium Chara: No Sporophyte Zygote Essentially four spores per fertilization (corresponding to the typically 4 meiotic products)
Development of the sporophyte prior to meiosis Diploid parent (Sporophyte) Meiosis (delayed) Diploid zygote Haploid Spores Sperm (gamete) Egg ( gamete) Haploid parent (Gametophyte) Delaying Meiosis
Diploid phase Syngamy Meiosis Gametes Spores Haploid phase A of G, Simplified!
Defining Plant Derived Traits Hence plants are described as embryophytes
Embryo Retention (Analogy) We’ve seen embryo retention before… But in plants the embryo is dependent on parent for nutrients
Defining Plant Derived Traits An apical meristem is the cell division that takes place at the tips of stems and roots
Bryophytes have flagellated sperm and disseminate using spores (not pollen) Bryophytes We will mostly concern ourselves with phylum Bryophyta
Liverworts Longer-lived (conspicuous) gametophyte
Hornworts Longer-lived (conspicuous) gametophyte
Mosses Longer-lived (conspicuous) gametophyte
Seedless Vascular Plants We will mostly concern ourselves with phylum Pterophyta
Fern Sporophytes Longer-lived and larger (conspicuous) sporophyte
Innovation: Different Spore Types Seen in most non-seed bearing plants Seen mostly in seed bearing plants
When “Ferns” ruled the Earth! “Artists conception of a Carboniferous forest based on fossil evidence. Most of the large trees with straight trunks are lycophytes. The tree on the left with feathery branches is a horsetail. Tree ferns, not shown, here, were also abundant in the ‘coal forests’ of the Carboniferous.” p. 574, Campbell & Reece (2005)