Chapters 29 & 30: Plant Diversity AP Biology 2013 1 Chara species, a pond organism 5 mm Colonization of the Land Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) Since colonizing land, plants have diversified into about 290,000 species Evolved from green algae 40 µm Charophyceans are closest relatives of land plants and share these characteristics: 29.3 Rose-shaped complexes for cellulose synthesis 1 Origin of land plants (about 475 mya) 2 Origin of vascular plants (about 425 mya) 3 Origin of extant seed plants (about 305 mya) Hornworts Seed plants 450 400 350 300 50 0 Millions of years ago (mya) Plants have been on land for at least 475 million years 29.7 Derived Adaptations Chlorophytes Mitosis n Plantae 29.4 Embryophytes Gamete from another plant Mitosis Viridiplantae ANCESTRAL ALGA Charophytes Plants differ from charophyceans in five key ways: 2 Red algae Streptophyta So closely related to green algae that some think they should be included as plants Apical meristems Vascular plants Pterophytes (ferns, horsetails, whisk ferns) 3 500 Haploid Diploid n n Gamete n 2n Multicellular gametangia Multicellular dependent embryos Seedless vascular plants Lycophytes (club mosses, spike mosses, quillworts) 2 Formation of phragmoplast (aids in cell plate formation) Walled spores produced in sporangia Land plants Mosses Structure of flagellated sperm Alteration of generations Liverworts ANCESTRAL 1 GREEN ALGA Nonvascular plants (bryophytes) Peroxisome enzyme Zygote Mitosis Alternation of generations 29.5 3
Important Plant Terminology produces spores in organs called sporangia 29.5 s Diploid cells called sporocytes undergo meiosis to generate haploid spores Longitudinal section of Sphagnum sporangium (LM) Gametes are produced within organs called gametangia s and sporangia of Sphagnum (a moss) gametangia are called archegonia (produce eggs and are site of fertilization) Male gametangia are called antheridia (produce and release sprem) Archegonia, each with an egg (yellow) Antheridia (brown), containing sperm 29.5 Male 4 Archegonia and antheridia of Marchantia (a liverwort) Important Plant Terminology Apical Meristems - where plants exhibit continual growth Developing leaves Apical meristem of shoot 29.5 Apical meristems of plant roots and shoots Cells here can differentiate into various tissues Cuticle - waxy coating of the epidermis Apical meristem of root Mycorrhizae - symbiotic association bet ween plants and fungi that helps plants obtain nutrients Root Shoot 100 µm 100 µm Seed - an embryo surrounded by a protective coat Seed plants form a clade that can be divided into the clades gymnosperm and angiosperm Plants are grouped based on presence of vascular tissue 5 Bryophytes Nonvascular plants Represented by three phyla of small herbaceous (nonwoody) plants Bud Haploid Diploid s Gametophore dispersal Peristome Mature s Mosses - phylum Bryophyta Archegonia Rhizoid Zygote (within archegonium) Seta Capsule (sporangium) Foot Embryo Archegonium Young 2 mm Sequence of bryophyte evolution is not clear, but mosses are most closely related to vascular plants Antheridia Male Egg Liver worts - phylum Hepatophyta Hornworts - phylum Anthocerophyta Protonemata Bud Capsule with peristome (LM) s An Anthoceros hornwort species 29.8 Polytrichum commune, hairy-cap moss Capsule In all three phyla, s are larger and longer-living than s Seta (a sturdy plant that takes months to grow) 29.9 6
Importance of Mosses Capable of inhabiting diverse and extreme environments (although most common in moist forests and wetlands) Help retain nitrogen in soil Sphagnum (peat moss) forms deposits of partially decayed organic material called peat which can be used for fuel Reservoir for organic carbon Overharvesting or water level drop could cause stored CO2 to be released into the atmosphere RESULTS Annual nitrogen loss (kg/ha) (a) 6 5 4 3 2 1 0 With moss Peat being harvested from a peatland Without moss (b) 29.10 29.11 Tollund Man, a bog mummy dating from 405 100 B.C.E. 7 Seedless Vascular Plants Date back to 420 million years ago Vascular tissue allowed the plants to grow tall Have flagellated sperm (require moist environments) Early tiny plants had independent, branching s but lacked the other derived traits of vascular plants s are the larger generation; s are tiny plants that grown on or below the soil surface Haploid Diploid Sorus dispersal Fiddlehead (young leaf) Mature Young New Rhizoid Underside of mature Zygote Archegonium Egg Antheridium 29.13 8 Leaves - organs that increase surface area of vascular plants (capture more solar energy) Two types: Microphylls - with a single vein (perhaps evolved from outgrowths of stems) Megaphylls - highly branched vascular system (perhaps evolved from webbing of flattened branches) Sporophylls - modified leaves with sporangia Most seedless vascular plants are homosporous. Seed plants and some seedless vascular plants are heterosporous Evolution of Leaves Vascular tissue Sporangia Microphyll (a) Microphylls (b) Megaphylls Overtopping growth Other stems become reduced and flattened. Megaphyll Webbing develops. 29.14 9
Seedless Vascular Plant Phyla Lycophyta - club mosses, spike mosses, and quillworts Isoetes gunnii, a quillwort Selaginella moellendorffii, a spike moss 2.5 cm Strobili (clusters of sporophylls) Small herbaceous plants 1 cm Pterophyta - ferns, horsetails, and whisk ferns Ferns - most diverse group Diphasiastrum tristachyum, a club moss Equisetum arvense, field horsetail Athyrium filix-femina, lady fern These phyla formed the first forests during the Carboniferous period Vegetative stem 1.5 cm 25 cm Strobilus on fertile stem Psilotum nudum, a whisk fern Caused major global cooling 4 cm Eventually became coal 29.15 10 Seeds Bearing Plants Changed the course of plant evolution PLANT GROUP Plants could become dormant Mosses and other nonvascular plants Dominant Reduced s are protected in ovules and pollen grains Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms) Reduced, independent (photosynthetic and free-living) Reduced (usually microscopic), dependent on surrounding tissue for nutrition Reduced, dependent on Dominant for nutrition Dominant Gymnosperm Microscopic female s inside ovulate cone Angiosperm Microscopic female s inside these parts of flowers Example Develop within the walls of spores and retained within the tissue of the parent Microscopic male s inside pollen cone Microscopic male s inside these parts of flowers 30.2 Heterospory Ovules and 11 Heterospory Seed plants evolved from plants that had megasporangia (produce megaspores that give rise to female s) Ovule consists of a megasporangium, megaspore, and protective integuments Seed plants evolved from plants that had microsporangia (produce microspores that give rise to male s - contained in pollen) grain germination involves pollen tube that discharges t wo sperm into the female within the ovule Pollination - transfer of pollen to the part of the seed plant that contains the ovules Immature ovulate cone 30.3 Integument wall Micropyle grain (a) Unfertilized ovule wall Egg nucleus Megaspore Megasporangium Seed coat Discharged sperm nucleus tube Male (b) Fertilized ovule Food supply Embryo (c) Gymnosperm seed Seed develops from the whole ovule embryo along with its food supply packaged in a protective coat 12
Conifers Include four plant phyla: Cycadophyta, Gingkophyta, Gnetophya, Coniferophyta 30.5 Cycas revoluta Ginkgo biloba leaves and Ginkgo biloba pollen-producing tree fleshy seeds Ovulate cones Gnetum Welwitschia Ephedra Common juniper Appear early in the fossil record Douglas fir Sequoia European larch Wollemi pine Bristlecone pine 13 Gymnosperm Life Cycle features: Dominance of generation Ovulate cone Megasporocyte Integument cone Microsporocytes Mature Megasporangium grain grains Microsporangia Microsporangium Development of seeds from fertilized ovules Role of pollen in transferring sperm to ovules Ovule Haploid Diploid Surviving megaspore Seedling Archegonium Seeds Food reserves nucleus Egg nucleus Seed coat Embryo (new ) tube 30.6 14 Flowering plants Seed plants that produce reproductive structures called flowers and fruits adaptation of angiosperms Flower is a specialized structure for sexual reproduction Most widespread and diverse of all plants 15
Stigma Stamen Flower and Fruits Anther Carpel Style Filament Specialized shoot with modified leaves Ovary Petal Sepal Tomato Sepals enclose the flower Petals brightly colored to attract pollinators Ovule Ruby grapefruit Nectarine Figs. 30.7-30.9 Hazelnut Stamens which produce pollen Wings Milkweed Carpels which produce ovules Seeds within berries Fruits consist of a mature ovary and can be dispersed by wind, water, or animals 16 Barbs Angiosperm Life Cycle Double fertilization occurs when a pollen tube discharges t wo sperm into the female within an ovule One sperm fertilizes the egg; the other combines with t wo nuclei in the center cell of the female and initiates development of a food-storing endosperm Mature flower on plant Microsporangium Anther Microsporocytes Ovule Ovary Germinating seed Microspore Generative cell Male (in pollen grain) Embryo Surviving megaspore Seed coat (embryo sac) Nucleus of developing endosperm (3n) Zygote Antipodal cells Central cell Synergids Egg grains Stigma Megasporangium Endosperm (3n) Seed Tube cell tube Style tube Egg nucleus Haploid Diploid Discharged sperm nuclei 30.10 Endosperm nourishes the developing embryo 17 Angiosperm Evolution Originated at least 140 million years ago Primitive fossils of 125 million-year-old angiosperms display both derived and primitive characteristics Thought that ancestors had separate pollen producing and ovule producing structures before they were combined into a single flower Carpel Stamen 5 cm (a) Archaefructus sinensis, a 125million-year-old fossil (b) Artist s reconstruction of Archaefructus sinensis 30.11 18
Basal Angiosperm Diversity Two groups: Star anise Monocots Orchid Lily Monocots - one cotyledon Eudicots - t wo cotyledons Water lily Amborella trichopoda Pygmy date palm Anther Basal angiosperms less derived Stigma Ovary Filament 30.13 Barley, a grass Eudicots Magnoliids - share some traits with basal angiosperms but are more closely related to monocots and eudicots California poppy Dog rose Pyrenean oak Snow pea Zucchini 19 Angiosperm Diversity Monocot Monocot Eudicot Roots Embryos Two cotyledons One cotyledon 30.13 Leaf venation Veins usually netlike Veins usually parallel Taproot (main root) usually present Root system usually fibrous (no main root) grain with one opening Stems Vascular tissue scattered Eudicot grain with three openings Flowers Vascular tissue usually arranged in ring Floral organs usually in multiples of three Floral organs usually in multiples of four or five 20 Links Bet ween and Animals Pollination of flowers by animals and transport of seeds by animals Crucial for sur vival of humans Food, wood, and medicines Humans are destroying habitats and causing extinction 21