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Plants II The Vascular Plants Hypericum sp. Photo by Alan Mulvey THE SEED PLANTS I Gymnosperms
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Evolution of the Seed Plants Heterosporous Seed: (embryo & stored food) Evolution of pollen Megagametophyte develops within ovule** Microgametophyte develops within pollen grain** Pollen grains evolved by reduction of male gametophyte & protection by pollen walls Both the male & female gametophytes were retained within the sporophytes
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Evolution of the seed One cell megaspore is retained within megasporangium It is protected by integument It develops into mature megagametophyte within the embryo sac After fertilization, it matures into the embryo (sporophyte)
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Lilium: Pollen Generative cell ( 2 sperms ) Tube cell Pollen wall
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Pine: Pollen Generative cell Tube cell Wings
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Evolutionary transition from a gametophyte to sporophyte dominance From Keeton, 1993
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The Gymnosperms: Characteristics (naked seed)** Water is not required for fertilization Mainly pollinated by wind Reproductive changes increased protection of gametes Have sunken stoma & thicker cuticles
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Seed Cone Cone Scale Two Seeds per Scale
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Pine: Leaf Sunken Soma EpidermisHypodermis
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Characteristics Cont.. Have secondary growth - all trees or shrubs Mostly evergreen Xylem has tracheids, lacks vessels (except some Gnetophytes) Phloem has sieve cells, lacks sieve tube members
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Progymnosperms An extinct group that arose in late Paleozoic Intermediate between seedless & seed plants Progymnosperms were ancestors of seed plants Evolved bifacial V.C. & wood (page 411)
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Seed Plants I - Gymnosperms Conifers – Coniferophyta Cycads – Cycadophyta Maidenhair tree – Ginkgophyta Gnetophytes – Gnetophyta
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Conifers: Phylum Coniferophyta evolved 290 MYO Constitute the largest group of gymnosperms (50 genera, 550 spp.) Include the tallest & largest trees ever (Giant redwood) Conifers (pine, fir, spruce) have great commercial value in temperate zones Leaves are either needles, long or short, as in pines, fir, spruce small flat, scale-like as in junipers, cypresses Mostly evergreen, monoecious
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White Pine: Pinus strobus
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White Pine
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: Twig &Needles White Pine : Twig &Needles
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White Pine Pollen ConesSeed Cone
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Longleaf Pine: Pinus palustris
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Loblolly Pine: P. taeda
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Loblolly Pine: Pollen Cones
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Slash Pine: P. elliottii Turpentine Production
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Bald Cyprus Knees: Taxodium distichum Knees
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Bald Cyprus
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Bald Cyprus: Crown & Seed Cones
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Coast Red Wood: Sequoia sempervirens Fossil
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Sequoia: Coast Red Wood
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Giant Red Wood Sequoia http://www.habitas.org.uk/gardenflora/sequoiadendron.htm
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Giant Red Wood Seed Cones Pollen Cones http://www.conifers.org/cu/se2/
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Balsam Fir: Abies balsamea
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Balsam Fir Seed Cone Leaves
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Larch: Larix decidua
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Larch Developing cones
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Common Juniper: Juniperus communis Tree Leaves
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Juniperus virginiana (Eastern Red Cedar) Juniperus virginiana (Eastern Red Cedar) Cones
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Hemlock: Tsuga canadensis
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Hemlock: Leaf & Cone
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White Spruce: Picea glauca
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Pollen cones Young seed cones Pollinated seed cones White Spruce
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Pacific yew: Taxus brevifolia http://www.fw.vt.edu/dendro/dendrology/syllabus/tbrevifolia.htm
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Maidenhair tree Phylum Ginkgophyta: One extant species, Ginkgo biloba (notched leaf)** Reproduction is dioecious Ginkgo is resistant to air pollution (city parks) Pickled seeds are eaten in Asia Ginkgo is now cultivated, could be in the wild (Asia)
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Ginkgo biloba Leaves are broad with dichotomous venation
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The Ginkgo tree has properties which make it resistant to nuclear radiation. This tree survived the Hiroshima bombings. www.ginkgo.co.nz/images/ large/ginkgotree.jpg
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Ginkgo biloba
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Male cones Sperms are flagellated, borne in cone-like structure
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Ginkgo Brach & Fruit
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Ginkgo Seed Cones The fleshy part which covers the seed is the integument (offensive odor) No cones but ovules are borne in pairs and stalked
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Cycads: Phylum Cycadophyta About 250 MYO, common during the Mesozoic (age of cycads & Dinosaurs)** Constitute 11 genera (140 spp) Tropical or subtropical Zamia, the only cycad in the States, is native to Florida Most cycads are large palm-like plants Highly toxic (produce neurotoxins & carcinogenic compounds) Sperms are motile, but they are pollinated by beetles Dioecious
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Cycad: Encephalartos humlis
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Zamia floridana http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/cycadpg?taxname=Zamia+pumila Male/female cones
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Zamia: Cones Male Female
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Cycad: Encephalartos altensteinii http://www.calflora.net/southafrica/pageseventeen.html
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Cycad: Encephalartos ferox Native to Africa
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Encephalartos ferox
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Gnetophytes: Phylum Gnetophyta Comprise 3 genera (70 spp) The most derived group of gymnosperms Similarities to angiosperms: Produce vessels (in xylem) Their strobili are similar to angiosperms’ inflorescence Double fertilization in Ephedra & Gnetum Produce nectar & insects play a role in pollination Leaves are borne in opposite pairs
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The genus Gnetum Has 30 spp (trees & woody vines)*)* Native to SE Asia, tropical Africa, Amazon basin Have broad leathery leaves similar to dicot.
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Gnetum gnemon
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Gnetum: Leaf
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Gnetum: Pollen Cones
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Gnetum: Seed Cones
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The genus Ephedra Has 35 spp Tough shrubs inhabit deserts in N Mexico and SE USA** Leaves reduced and scale-like Dioecious or monoecious
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Ephedra - Cures respiratory problems - Used in weight loss prog. - A stimulant
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Ephedra: Pollen Cones
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Welwitschia mirabilis The most bizarre vascular plant** Native only to deserts of South Africa, Angola, & Namibia Dioecious
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Welwitschia - Most of the plant is buried in the sand - Aboveground discoid wide stem (1.5 m wide) produces 2 long leaves DISK
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Welwitschia Habitat http://www.csdl.tamu.edu/FLORA/imaxxwlw.htm Population
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Welwitschia Habitat
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Welwitschia Cones
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Welwitschia Male conesFemale cones
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