Plant Diversity IHow Plants Colonized Land(The Seedless Plants) Packet #33 Chapter #29
Introduction • There are more than 290,000 species of plants that inhabit the earth. • How, and why, based on the theory of evolution, did plants venture out of the sea and onto dry land? • Charophyceans • Green algae • Provides some of those answers
Information About Plants • Multicellular • Eukaryotic • Photoautotrophs • Cell walls made of cellulose • Chlorophylls a & b are present in land plants
Diversion of Algae and Land Plants • Embryophytes (plants with embryos) is the traditional scheme and equates with Kingdom Plante
Similarities Between Charophyceans & Land Plants Evidence That Plants Moved to Land
Morphological & Biochemical Evidence • It is thought that land plants evolved from green algae • Four Key Traits that “suggest” an evolutionary relationship between Charophyceans and Land Plants • Homologous peroxisomes • Both groups contain enzymes that minimize the loss of organic products due to photorespiration • Formation of phragomoplast • Synthesis of cell plates during cell division involves the formation of phragomoplast • Homologous Sperm • Many plants (gymnosperms) have flagellated sperm that match charophycean sperm • Homologous cellulose cell walls • Cell walls of both land plants and charophyceans contain 20-26% cellulose
Genetic Evidence • Key nuclear genes • Ribosomal RNA • Cytoskeleton proteins • In agreement with the biochemical and morphological data • Homologous chloroplasts • Algal plastids, of green algae and algal groups such as euglenoids, are similar to those found in land plants • Chloroplast DNA found in charophyceans, green algae, is most closely related to that found in land plants.
Adaptations Enabling the Move to Land • Charophyceans have a layer of a durable polymer called sporopollenin. • Prevents exposed zygotes from drying out. • May be the precursor to the tough sporopollenin walls that encase plant spores.
“Evolutionary” Adaptations to Terrestrial Living/Derived Traits for Terrestrial Living
Evolutionary Adaptations to Terrestrial Living • There are four main groups of land plants • Bryophytes • Pteridophytes • Gymnosperms • Angiosperms
Adaptations II • The colonization of land by plants required the evolution of many anatomical, physiological and reproductive adaptations
Adaptations III • Waxy Cuticle • Used to protect against water loss • Stomata • Gas exchange needed for photosynthesis
Adaptations IV • Plant Life Cycles • Alternation of Generation • Part of the life cycle is in a haploid gametophyte generation and part in a diploid sporophyte generation. • The gametophyte plant produces gametes via mitosis • During fertilization the gametes fuse together to form the zygote • The zygote is the first stage of the sporophyte generation.
Adaptations IV • Zygote develops into a multicellular embryo that the gametophyte protects and nourishes • Mature sporophyte plant develops from the embryo • Sporogenous cells (spore mother cells) are produced • Cells undergo meiosis to form spores • The spore is the first stage of the gametophyte generation.
Adaptations V • Most plants produce multicellulargametangia • Protective jacket of sterile cells surrounding gametes. • Gametophyte generation (More to come later) all produce their gametes within multicellular structures • Gametangia • Male Gametangium • Antheridium • Many sperm released into the environment when mature
Adaptations V • Female Gametangium • Archegonium • Produces a single egg cell and retains the egg within the organism
Adaptations VI • Production of Secondary Compounds • Plants produce many unique compounds as byproducts of primary metabolic pathways. • Byproducts help plant defend itself against herbivores • Compounds have bitter tastes, strong odors or toxic effects. • Compounds include terpenes, alkaloids and tannins.
Adaptations VII • Mosses and ferns, although adapted to life on land, have motile sperm cells that require water as a transport medium for fertilization. • Ferns, and vascular plants, that “evolved” at a later time, have xylem, to conduct water, and phloem, to conduct dissolved sugar.
Features That Distinguish Bryophytes From Green Algae and Other Plants The Bryophytes
Bryophytes • Have several adaptations that green algae lack • Cuticle • Stomata • Multi cellular gametangia
Bryophytes II • Non-vascular plants • Lack xylem • Lack pholem • Only plants with a dominant gametophyte generation. • Sporophytes remain permanently attached and nutritionally dependent on the gametophyte.
Phyla of Pryophytes Bryophytes
Phylum BryophytaThe Mosses • Have gametophytes that are green plants that grow from a filamentous protonema. • Green filamentous growth that arises from spore germination in liverworts and mosses and eventually gives rise to a mature gametophyte.
Phylum BryophytaThe Mosses • Gametophyte bears archegonia and/or antheridia at the top of the plant. • During fertilization, sperm cell fuses with an egg cell in the archegonium • Zygote grows into an embryo that develops into a moss sporophyte which is attached to the gametophyte. • Meiosis occurs within the capsule if the sporophyte to produce spores. • Spores are dispersed by wind. • Spore germinates. Grows into a protonema that forms a bud.
Gametophyte Sporangium Life Cycle of the Mosses
Sporangium Mature Sporangium Life Cycle of the Mosses
Germination Gametophyte Life Cycle of the Mosses
Phylum BryophytaThe Mosses • Bryophytes have been distributed around the world from the tropics to the arctic. • They can exist in dry or cold habitats • They can practically desiccate • Rehydrates following rain events. • One wetland moss, Sphagnum, forms extensive deposits of peat.
Phylum HepaticophytaThe Liverworts • Have gametophytes that are flattened, lobelikethalli. • Plant body, not differentiated into roots, stems and leaves, of some algae, fungi and similar simple plantlike organisms. • Others are leafy
Phylum AnthocerotophytaHornworts • Have thalloid gametophytes
Features That Distinguish Ferns and Other Seedless Vascular Plants From Algae and Bryophytes. Ferns
Ferns I • Comparison to Bryophytes • Ferns have vascular tissue • Ferns have a dominant sporophyte generation. • As in bryophytes, reproduction in ferns depends on water as a transport medium for their motile sperm cells.
Introduction I • Represent the modern groups that formed the forest during the evolutionary time period—The Carboniferous Period. • Organisms left relics, fossils and coals • Seed plants were present during this evolutionary time period but were not dominant. • Became important as the swamps dried up and the global climate cooled.
Introduction II • There are four phyla of seedless vascular plants. • Phylum Polypodiophyta • Ferns • Phylum Psilotophyta • Whisk ferns • Phylum Equisetophyta • Horsetail • Phylum Lycophyta • Club Mosses
Phylum PterophytaSubphylum PolypoiophytaThe Ferns • Largest and most diverse group of seedless vascular plants. • More than 12,000 species have been described. • Almost all species are homosporous (details to come) • All have megaphylls.
Phylum PterophytaSubphylum PolypoiophytaThe Ferns • Sprophytes have roots, rhizomes and leaves that are megaphylls. • Leaves, or fronds, bear sporangia in clusters called sori. • Meiosis of sporangia produces haploid spores. • Fern gametophyte, called a prothallus, develops from a haploid spore and bears both archegonia and antheridia.
Keywords • Homospory • The production of one kind of spore • Bryophytes • Whisk ferns • Horsetails • Most club mosses • Most ferns • Spore gives rise to gametophyte plants that produce both egg and sperm cells.
Keywords II • Heterospory • Production of two kinds of spores • Microspores • Give rise to male gametophytes that produce sperm cells • Megaspores • Give rise to female gametophytes that produce eggs. • Occurs in • Certain club mosses • Certain ferns • ALL SEED PLANTS. • The “evolution” of heterospory was an essential step in the evolution of seeds.
Phylum PterophytaSubphylum PsilotophytaThe Whisk Ferns • Lack true roots and leaves • Consists of dichotomously branching rhizomes • Have erect stems. • Homosporous sporophylls.
Phylum PterophytaSubphylum EquisetophytaThe Horsetails • Sporophytes have roots • Rhizomes • Aerial stems • Hollow and jointed • Leaves that are reduced megaphylls
Phylum LycophytaThe Club Mosses • Consist of roots • Rhizomes • Erect branches • Leaves that are microphylls.