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Download 1 Plant Diversity General Plants are classified into 4 major groups
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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 and leathery most leaves have thick waxy cuticle 3. many conifers produce resin = viscous, clear organic substance that may protect plant from fungal and insect attack resin collects in resin ducts = tubelike cavities that extend throughout roots, stems and leaves resin is produced by cells lining resin ducts Woody Stems Conifers and flowering plants are the only major plant groups that have perennial species Plants that live more than one year, ie. perennials, produce secondary growth each year. In woody plants there are two major layers of embryonic cells (lateral meristem) called the cambium, that produces this secondary growth each year. 1. Vascular Cambium One layer of cambium is found in the vascular bundles of the stem between the xylem and phloem. Each year this cambium produces new layers of xylem and phloem cells. Xylem grows much faster than phloem and virtually all of the “wood” of a tree is dead xylem cells Plants: Plant Classification – General, Ziser, 2003 12 the oldest cells are closer to the center of the trunk Each year the cambium lays down a new layer of xylem the old wood closest to the center expands as new cells are laid down in the vascular cambium these older cells are often darker and are called heartwood. vs sapwood (still used for transport) Differences in the size of the cells produced throughout the growing season produce the familiar “growth rings” in the wood. softwood vs hardwood the arrangement of different cell types in the secondary tissue results in the distinctive characteristics of each kind of wood: eg oak, maple, pine, etc Most of the strength of wood comes from the sclerenchyma cells of the xylem specifically the tracheids, vessel elements and fibers thickness of the trunk requires rays for lateral transport = chains of parenchyma cells that radiate out from center of stem typically continuous with the secondary xylem and phloem the layers of phloem are much thinner and become part of the bark The phloem, on the “outer-side” of the cambium, the cortex and the periderm make up the bark of a tree. 2. Cork Cambium Another layer of cambium is located between the cortex and epidermis, this produces periderm Plants: Plant Classification – General, Ziser, 2003 13 which makes up most of the bark of woody plants. The bark replaces the epidermis for protection of the stem in large woody plants. cork cambium can form a continuous cylinder of dividing cells (similar to vascular cambium in woody stems) or a series of small arcs producing furrowed bark the thickness, patterns and texture of bark vary considerably by species largely because of the varying growth rates of cork cambium in different tree species the bark contains cork cells dead at maturity heavily waterproofed cell walls protects against injury, mild fires, temperature extremes, water loss areas of bark where cork cells are loosely arranged = lenticels allow gas exchange wood is typically produced in the stem (=trunk) but major roots of trees also usually have wood, bark and annual rings Life Cycle: Mosses Ferns Conifers gametophyte was dominant sporophyte a temporary structure growing on gametophyte sporophyte was dominant, separate from gametophyte gametophyte was small temporary prothallium sporophyte is dominant plant gametophyte greatly reduced, temporary, and completely dependent on sporophyte in gymnosperms the sporophyte is the dominant stage there is no free living gametophyte instead, gametophyte is attached to and nutritionally dependent upon sporophyte Plants: Plant Classification – General, Ziser, 2003 14 both gymnosperms and angiosperms are heterosporous produce two types of spores: microspores megaspores most conifers are monoecious (hermaphrodites) with separate male and female cones in different locations of same plant reproductive organs are cones (=strobili) Female Gametophyte ovule – produced on female cone female cone: much larger than male takes 2 years to mature not terminal In early spring the ovulate or seed cone begins to develop Takes 2 years to develop consists of a central axis bearing a series of bracts and scales (=modified leaves) two ovules develop on upperside of each bract some conifers do not produce woody female cones eg. yews: seed is almost completely surrounded by fleshy cuplike covering, an outgrowth from base of seed seed covering is red and attracts birds which eat it and disperse the seeds eg. Junipers bear seeds in fleshy cones that resemble berries fleshy scales are fused together and completely enclose seed birds eat and disperse seeds cones used to flavor gin Male Gametophyte =pollen grain produced in male cone male cone: terminal on short branches Plants: Plant Classification – General, Ziser, 2003 15 ~ half inch long or less produce pollen consists of 2 cell walls enclosing 3 cells prothallial cells (2) degenerate) generative cell air sacs (for bouyancy) tube cell Pollen grains blow around until they contact micropyle of female gametophyte Pollen tube develops from tube cell of pollen generative cell produces sperm nuclei which travel down pollen tube to egg and fertilize it = zygote the fertilized egg develops into mature seed consisting of several structures: ~8 cotyledons (surround epicotyl) seed coat hypocotyl Economic Importance of Conifers: conifers are the most important phylum of gymnosperms both ecologically and commercially conifers are the predominant trees in 35% of the world’s forests they play an essential ecological role: 1. roots hold soil in place and reduce soil erosion 2. watersheds – absorb hold and slowly release water and help control flooding 3. food and shelter for other organisms coniferous forests are economically important: 1. recreation camping backpacking picknicing Plants: Plant Classification – General, Ziser, 2003 16 2. in US ~80% of timber crop is from conifers: building and paper products landscaping christmas trees resin of some plants is used to make turpentine, tar, etc Plants: Plant Classification – General, Ziser, 2003 17 Flowering Plants [Angiosperms] 235,000 known species =vascular plants that reproduce sexually by forming flowers and fruits dominant plants in world today last major group to appear in the fossil record 1st appeared 130 MY ago have dominated the landscape for the last 100 Million years Why are flowering plants so successful: 1. highly adaptable vegetative organs including complex symbioses with fungi and bacteria enhance survival 2. form and diversity of leaves maximize photosynthetic efficiency 3. much more efficient transport tissues structure of both xylem and phloem are more efficient than in gymnosperms 4. diversity in flower structure greatly enhances success and diversity of group 5. seed within fruit better protection much greater variety of dispersal differences from gymnosperms: more efficient vascular tissues: sieve cells smaller in gymnosperms, larger and with more pores in angiosperms few gymnosperms have xylem vessels, mainly have tracheids angiosperms have flower instead of cone angiosperms surround seed with fruit Two major groups of flowering plants: monocots ~65,000 species Plants: Plant Classification – General, Ziser, 2003 18 flower parts in three’s parallel veined leaves onions, grasses, irises, lilies, only woody monocots are palms eg coconut palm dicots more diverse, (>170,000 species) flower parts in 4’s or 5’s net veined leaves oaks, roses, mustards, cacti, sunflowers includes herbs, shrubs and trees Flower Structure in flowering plants, sexual reproduction occurs in flowers sepals petals stamens = filament + anther pistils = stigma + style + ovary are temporary structures parts are arranged in whorls on the end of a flower stalk = peduncle peduncle may terminate in a single flower or a cluster of flowers = inflorescence tip of peduncle enlarges to form the receptacle sepals lowermost whorl leaflike covers and protects flower bud all sepals together = calyx petals whorl just above (inside) sepals great variation in size, shape and color sometimes fused to form tube all petals together = corolla stamens just inside petals consist of filament and anthers Plants: Plant Classification – General, Ziser, 2003 19 anther = sac like structure that produces pollen grains (=gametophytes) each pollen grain produces 2 cells surrounded by tough outer wall one cell contains 2 male gamete (sperm) nuclei other cell produces pollen tube through which sperm nuclei travel to ovule pistil female reproductive organs may be a single chamber or made of a group of chambers = carpels sometimes carpels are fused into a single pistil sometimes there are many pistils each pistil consists of: stigma on which pollen lands necklike structure style saclike, contains ovule ovary each ovule contains cells that form one egg and 2 polar nuclei many variations in flower structure a flower with all four different parts lacking one or more with both stamens and carpels stamens or carpels = = = = complete flower incomplete perfect imperfect some of these variations are due to the way flowers are pollinated pollen grains must travel from anther of one flower to stigma of another self pollination pollen travels to stigma of same flower cross pollination pollen travels to stigma of different plant flowering plants have coevolved with many kinds of animals through most of their history this close interdependent relationship between Plants: Plant Classification – General, Ziser, 2003 20 plants and pollinators has resulted in coevolution mutual adaptations for mutual benefits plant: petals, scent, nectaries animal: special body parts and behaviors In some instances the relationships have become very specialized such that only a single species of animal can pollinate a particular species of plant. 1. wind pollinated often grow in dense populations many small inconspicuous flowers petals reduced pistils and stamens exposed numerous stamens and conspicuous large amounts of pollen produced eg. oak, willow, grasses insect pollenators - general petals colorful and large often with nectaries fused petals force insect to crawl into flower for nectar 2. sunflowers are a successful exception to above: they are insect pollinated but consist of numerous inconspicuous flowers they combine to resemble a single, large showy flower one insect pollinates many flowers at once 3. bee pollinated 20,000 different species of bees are important pollinators for many plants honeybees are attracted to nectar they also gather pollen flowers are generally brightly colored predominately blue or yellow rarely pure red (pure red appears black to them) flowers often have lines or distinctive markings that function as “honey guides” lead bees to nectar some of these markings are only seen in UV light Plants: Plant Classification – General, Ziser, 2003 21 invisible to us, not bees flowers often delicately sweet and fragrant 4. beetle pollinated flowers tend to have a strong yeasty, spicy or fruity odor usually white or dull in color (beetles cant see as well as bees) secrete no nectar but may supply food as pollen or in special storage cells in petals 5. carrion flies tend to be dull red or brown often have foul odors resembling rotting meat eg. carrion flowers (Africa); skunk cabbage 6. butterflies similar to bee-pollinated flowers in that they have sweet fragrances nectaries are usually at bases of deep spur that only butterflies and moths can reach with their mouthparts some butterflies can detect red flowers eg. daisy family: butterfly bush= Buddelias, goldenrods, blazing star eg. milkweeds monarchs 7. moth pollinated white or yellow flowers heavy fragrance open at dusk eg. some yuccas, some milkweds (see p510 Stern 3rd ed) 8. bat pollinated mainly in tropics strong odor dull color open only at night 9. hummingbirds do not have a highly developed sense of smell but do have excellent sense of vision frequently bright red or yellow flowers little if any odor fused petals with nectary Plants: Plant Classification – General, Ziser, 2003 22 produce copius quantities of nectar long floral tubes prevent most insects from reaching the nectar eg. fuschias, petunias, morning glories, salvias, cardinal flowers, trumpet creepers, columbines, penstemons 10. orchids some speceis of orchids resemble certain wasp females see Stern p 512-14 Plants: Plant Classification – General, Ziser, 2003 23 Role of Pollinators in Modern World without pollinators many plants cannot be fertilized to produce seeds 90% of worlds flowering plants are animal pollinated including 80% of world’s 1330 cultivated crop species 1/3rd of US agricultural crops are insect pollinated 120,000 – 200,000 animal species are pollinators including >1000 sp of birds and mammals honeybee pollination services are 60-100x’s more valuable than the honey they produce in US ~1/2 of honeybee colonies have been lost in last 50 years 25% in last 5 yrs alone threats: habitat fragmentation loss of nesting and overwintering sites intense exposure to pesticides and herbicides introduction of exotic species Plants: Plant Classification – General, Ziser, 2003 24 Fertilization: one of the two cells in pollen grain grows a thin pollen tube down through the style into the ovule the 2nd cell divides to form two sperm cells which move down the pollen tube ad enter the ovule only flowering plants have double fertilization zygote endosperm this double fertilization results in seed: young plant embryo nutritive tissue = endosperm seed coat The Seed: seed = plant embryo with stored nutrients in protective shell mature seed consists of: 1. embryo: radicle = embryonic root hypocotyl = embryonic shoot (stem) cotyledons = seed leaves (monocot has 1 cotyledon dicots have 2 cotyledons) plumule (=epicotyl) = part of shoot above leaves 2. food food is stored either in the cotyledon or in endosperm (a nutritive tissue surrounding embryo) the nutrients are used by the germinating seed until true leaves can begin photosynthesis in monocots the endosperm is main source of food in mature seed in most dicots – endosperm nourishes embryo which subsequently stores food in its cotyledons 3. Seed Coat tough, for protection Plants: Plant Classification – General, Ziser, 2003 25 seed size varies from: eg. dustlike orchids eg. 60lbs double coconut The Fruit seeds are not naked as in most gymnosperms the ovary wall enlarges into a fruit protects developing seeds from desiccation aids in dispersal As the ovule develops into a seed the ovary portion of the pistil increases greatly in size and becomes a fruit fruit = a ripened ovary containing seeds eg. pea pod = fruit; peas = seeds peach, bean and watermelon all develop from ovaries only 1/8th to 1/4th inch in diameter causes great drain on food supply vegetative growth often ceases when fruits are developing pinching off some flower buds results in larger fruits that are left The tissues of fruit and seed enhance survival and may aid in dispersal distribute new plants to areas away from parent plant There are many different kinds of fruits characterized by how they develop and the arrangement of the flower parts that produced them 4 basic types: 1. simple: develops from a flower with single pistil eg. tomato, grape, bean, pea, wheat, corn 2. aggregate develops from flower with may separate ovaries eg. rasberry, blackberry, magnolias 3. multiple develops from an inflorescence, ovaries fuse to form single Plants: Plant Classification – General, Ziser, 2003 26 fruit eg. pineapple, mulberry, figs 4. accessory develop from flower in which receptacle or floral tube enlarges and becomes part of the mature fruit eg. apple, pears (=pomes outer part of fruit is enlarged floral tube), strawberry (edible portion of strawberry is fleshy receptacle) most fruits are simple fruits at maturity simple fruits may be fleshy or dry fleshy: dry: berry: eg tomato, brapes, blueberries, cranberries, bananas drupe: contain hard stony pit surrounding single seed eg. peaches, plums, olives, avocados, almonds [NOT: strawberries, rasberries, mulberries] some split open along seams or sutures to release seeds follicle: splits along 1 suture eg. milkweed legume splits along 2 sutures eg. peas, beans, bluebonnets capsule splits along multiple sutures eg. poppies, cotton, some do not split along sutures grain (caryopsis) single seed, seedcoat fused to fruit eg. corn, wheat achene same as grain but seed coat is not fused eg. sunflowers, daisies, composites nuts usually larger, often from compound pistil eg. chestnuts, acorns, hazelnuts [NOT: peanuts, brazilnuts Seed Dispersal Mechanisms: 1. wind one of most important Plants: Plant Classification – General, Ziser, 2003 27 a. small, light seeds eg. orchids seeds resemble dust b. hairlike appendages eg. dandelions, milkweeds c. winged seeds eg. maple, bigonia d. whole plant dispersal eg. tumbleweed (=Russian thistle) 2. edible fruits attracts birds or mammals may eat whole fruit or spit out pits if swallowed seeds resistant to digestive juices squirrels and birds bury fruits and seeds nuts stored underground are forgotten 3. passively carried by animals hooks or spines to catch in fur or on skin in mud on feet of birds, etc. burs, beggars ticks, devils claw, etc. 4. water dispersal aquatic plants rainfall some contain airsacs to float mangroves, coconuts 5. mechanical dispersal =explosive dehiscence seeds are forcibly ejected from fruit many cast seeds several feet away from parent plant eg. violets Economic Value of Flowering Plants virtually all crop plants are flowering plants cooking oils spices and seasonings Plants: Plant Classification – General, Ziser, 2003 28 hardwoods are used for furniture and flooring musical instruments commercial products: latex/rubber maple syrup sugar pharmaceuticals extracted nightshade belladonna atropine jimsonweed scopolamine hallucinogenic native Americans used for puberty rights and rituals cork from bark of cork tree baskets paper Plants: Plant Classification – General, Ziser, 2003 29