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1 Plant Diversity General Plants Are Classified Into 4 Major Groups Plant Diversity General Plants are classified into 4 major groups: from simplest to most complex from oldest to most recently evolved Mosses (~15,000 species) small, simple, in moist habitats, oldest fossils Ferns (11,000 species) more complex tissues and organs, Conifers (760 species) mostly trees and shrubs, reproduction by producing pollen, and seeds in “cones” Flowering Plants (235,000 species, 90% all plants) most complex in terms of structure reproduce by producing pollen, and seeds in fruits Plants: Plant Classification – General, Ziser, 2003 1 Mosses & Allies (several other phyla of plants have the word “moss” in their common names but they are NOT really mosses they just resemble them in some way) ~15,000 species eg. mosses, liverworts, hornworts simplest of plants most are small (<20 cm) and inconspicuous grow along streams or on moist soil, rocks and tree trunks are ancient plants most are tropical they apparently developed from a green alga as a “dead end” group not in direct path of evolution (ie. vascular plants did not have moss ancestors) plants that were first able to leave aquatic environment and move onto land generally poorly adapted to land tend to live in moist places live in dense beds on moist soil, rocks or bark still tied to water for reproduction thin cuticle in most, some lack it no water distribution system: no vascular tissue absorb water through epidermis (like sponge) no true roots, stems or leaves (since no vascular tissue) each individual plant has tiny root-like rhizoids for attachment (not to absorb nutrients for the plant) slender stemlike structure bears leaflike blades Plants: Plant Classification – General, Ziser, 2003 2 can grow upright or along ground weak (no lignin) Reproduction and Life Cycle: show basic alternation of generations with gametophyte the dominant form in the life cycle it is larger it is often perennial while the sporophyte is temporary it provides nutrition for sporophyte gametophyte Structure (true mosses): leafy green often perennial bears gametangia at tip of “stalk” antheridia sperm cells archegonia eggs many species have separate male and female plants flagellated sperm are released from antheridia during rainy weather and transported by splashing of raindrops once they get to female plant, sperm cell swims down neck of archegonium and fuses with egg = zygote the zygote grows into a sporophyte sporophyte remains attached to the gametophyte for nutrition foot = embedded in tip of gametophyte to anchor it seta = stalk capsule = sporangium – contains up to 50M haploid spores when spores are mature, capsule bursts open as it dries out wind or rain carry spores to new areas where they germinate Ecological Importance: Plants: Plant Classification – General, Ziser, 2003 3 Pioneer Plants colonize bare rock produce acids that help in soil formation hold soil in place and help prevent erosion along streams some birds (eg. waxwings) use moss as nesting material peat bogs: major carbon reserves eg. Sphagnum =>help to absorb CO2 and stabilize climate used for fuel in England and some northern countries mosses are sensitive indicators of air pollution Plants: Plant Classification – General, Ziser, 2003 4 Ferns and Allies (Seedless Vascular Plants) Vascular Plants virtually all plants other than mosses and allies have vascular tissue vascular system enables plants attain greater size: some ferns (tropical) grow to 75 feet today vascular plants have true stems most have vascularized roots and leaves ancestors of vascular plants also evolved from green algae Ferns & Allies 11,000 species mostly terrestrial, a few are aquatic range from tropics to arctic but most are tropical epiphytes in temperate regions ferns typically inhabit swamps and moist areas most common fern in the world is bracken fern (=Pteridium aquilinum) grows well in poor soil – uncommon fern trait have true stems, roots, and leaves Stems rhizome = underground stem with wiry roots in temperate areas rhizome produces new leaves each spring ferns are easily propagated by rhizome cuttings Plants: Plant Classification – General, Ziser, 2003 5 Roots the roots are clearly differentiated from stem Leaves frond = large, compound leaves used for photosynthesis and reproduction when each young frond emerges from ground it is tightly coiled fiddlehead as fiddlehead grows it unrolls and expands to form frond Reproduction and Life Cycle ferns show clear alternation of generations most ferns are annuals fern life cycle 4-18 months sporophyte stage is dominant the “fern” we see are sporophytes fern sporophytes are perennial sporophyte produces asexual spores spore production occurs on underside of leaf in clusters of sporangia called sori sometimes sori are covered by umbrella-like indusium [size of a pinhead] as humidity changes sporangia break open throwing spores into air Gametophyte Stage gametophyte generation of ferns is completely separate and bears no resemblance to sporophyte spores germinate into gametophytes called a prothallium Plants: Plant Classification – General, Ziser, 2003 6 gametophyte is tiny (~1/4 inch) often heart shaped as prothallium matures it produces male and female reproductive organs =antheridia & archegonia archegonia located in central region near notch each contains a single egg antheridia scattered among rhizoids sperm cells shaped like cork screws ferns require water for fertilization as young sporophyte develops the prothallium withers and dies. Ecological and Economic Uses of Ferns & Allies help soil formation and prevent erosion probably most significant contribution to human culture is as coal deposits carboniferous fern forests are widely cultivated for horticultural value the fiddlehead of some species are harvested in early spring , bilied or steamed and eaten esp in New England and Canada eg. ostrich fern Matteaccia horsetails have a hollow jointed stems impregnated with silica gritty texture (=scouring rushes) first “brillo pads” Plants: Plant Classification – General, Ziser, 2003 7 Seed Plants mosses are small, nonvascular plants that generally are found in moist habitats and require water for reproduction ferns, though more terrestrial, with vascular tissue and better able to survive in drier habitats still require water for sexual reproduction both of these groups are relatively rare today and found in only a few habitats. most plants today are Seed Plants (gymnosperms & angiosperms) seed plants are much more successful at life on land 1. they are no longer tied to water, even for reproduction 2. they generally have a much more efficient vascular system but most of their success can probably be attributed to three major adaptations: 1. Greatly reduced alternation of generations sporophyte no longer produces spores for reproduction and dispersal sexual reproduction becomes the primary method of reproduction and dispersal instead sporophyte produces microscopic gametophytes that become the main means of reproduction and dispersal 2. Pollen male gametophyte = pollen dispersed by wind (not water) to the female Also offers a wider variety of methods of Plants: Plant Classification – General, Ziser, 2003 8 genetic variation 3. Seed female gametophyte remains attached to sporophyte plant as ovule once fertilized, ovule develops into seed seed = embryonic plant unlike spore which is a single cell, seed already has an embryonic root, stem and leaf plus stored food supply for germination, surrounded by protective seed coat in nonseed plants the asexual spore is the primary means of dispersal seed replaces the spore as the main means of reproduction is much more effective, and resistant to drying in non-seed plants, the embryo develops from the fertilized egg in the archegonium and immediately grows to maturity in seed plants the embryo reaches a certain size, goes dormant, and becomes an important means of dispersal Sexual reproduction becomes the main means of reproduction greater variation evolutionary advantage seeds and seed plants are strongly connected with the development of human civilization as an important food source: seeds are: easy to store easy to germinate Plants: Plant Classification – General, Ziser, 2003 9 generally have high nutritional value Plants: Plant Classification – General, Ziser, 2003 10 Conifers & Allies 760 sp of gymnosperms conifers are one of a group of plants called gymnosperms or “naked seeds” they produce seeds that are either totally exposed or borne on the scales of the female cone the seeds are not produced inside a flower and fruit they are exposed usually on a cone gymnosperms include: conifers: pine, cedar, spruce, fir, sequoias, etc cycads (resemble palms) ginkoes gnetophytes by far the most abundant gymnosperms are the conifers nearly all are woody trees, shrubs and vines conifers group contains some of the world’s a. most massive organisms: “General Sherman” giant sequoia - California 272’ (81.6m) tall 79’ girth; >25’ diameter b. world’s tallest tree: Coastal Redwood 385’ (117m) tall c. oldest living trees bristlecone pines one is over 4900 years old Conifer Characteristics: 1. nearly all conifers are evergreen: can carry out photosynthesis even in winter to some degree Plants: Plant Classification – General, Ziser, 2003 11 in spring they can increase photosynthesis immediately (don’t have to grow new leaves) each leaf lives 2-14 years and falls off individually a few are deciduous, eg.: dawn redwood, larch, bald cypress 2. in most leaves are needle or scale shaped to survive dry conditions (desert, snow) leaves are long, narrow, tough
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