Chapter 17 Seedless Vascular A

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Chapter 17 Seedless Vascular Plants

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Outline Evolution of vascular plants Organization of the vascular plant body Reproductive systems Phyla of seedless vascular plants P. Rhyniophyta (extinct) P. Zosterophllophyta (extinct) P. Trimerophytophyta (extinct) P. Lycopodiophyta P. Pterophyta

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Evolution of Seedless Vascular Plants Similarities btwn bryophytes and vascular plants alteration of heteromorphic generation Differences btwn bryophytes and vascular plants bryophytes dominant, free-living gametophyte nutritionally dependent sporophyte water-dependent reproduction b/c swimming sperm lack lignified vascular tissue (X and P) subapical meristem results in ↓ branching (1 sporangium) vascular plants dominant, free-living sporophyte nutritionally dependent gametophyte lignified vascular tissue allows ↑ size b/c water transport + rigid CW apical meristem allows ↑ branching (multiple sporangia)

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Evolution of Seedless Vascular Plants Trends in plant evolution mvmt from water to land increasing independence from water reproduction vascular tissues greater specialization via tissue differentiation 1st vascular plants little differentiation roots for anchorage, stems/lvs for Ps reduction of gametophytic generations seeds in one evolutionary line provide protection/nutrients Seedless vascular plants several phyla extinct 7 phyla w/ living representatives Cooksonia 418 MYA

Organization of the Vascular Plant Body: 

Organization of the Vascular Plant Body Amanda’s Talk Terms root system, shoot system 3 tissue systems (dermal, vascular, ground) xylem and phloem 1° growth, tissues, plant body 2° growth, tissues, plant body vascular cambium, cork cambium, periderm tracheary elements, tracheids, vessel elements pith, stele, leaf traces, leaf gaps, leaf trace gaps protostele, siphonostele, eustele microphylls, megaphylls

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Reproductive System All vascular plants are oogamous and exhibit alteration of heteromorphic generations (sporophyte dominant) oogamous = large, nonmobile egg and small, mobile sperm Vascular plants are homosporous or heterosporous homosporous = 1 type of spore (equisetophytes, lycophytes, Pterophyta) spores produce bisexual gametophytes ferns functionally unisexual b/c different maturity times heterosporous = 2 types of spores (lycophytes, Pterophyta, all seed plants), evolved later microspores produced in microsporangia become ♂ gametophyte (a.k.a. microgametophyte) megaspores produced in megasporangia become ♀ gametophyte (a.k.a. megagametophyte) unisexual gametophytes

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Reproductive System Gametophytes of homosporous plants larger, independent of sporophyte, photosynthetic Gametophytes of heterosporous plants smaller, dependent of sporophyte Evolutionary trend in vascular plants ↓ of gametophyte size/complexity mature megagametophytes of angiosperms = 7 cells (1 egg) mature microgametophytes of angiosperms = 3 cells (2 sperm) pollen grains = microgametophytes of angio-/gymnosperms loss of archegonia and anthredia present in seedless vascular plants, absent in angiosperms archegonia present in gymnosperms but anthredia absent loss of swimming sperm instead wind, animal pollination

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Phyla of Seedless Vascular Plants Rhyniophyta/Zosterophyllophyta/Trimerophytophyta prominent during Devonian period (360 - 408 MYA) extinct Progymnospermophyta gives rise to seed plants 4 major groups of seedless vascular plants early vascular plants (Rhynio-/Zosterophyllo-/Trimerophytophyta) small, simple, primitive morphology, 370-425 MYA, extinct pteridophytes/lycophytes/progymnosperms more complex, 290-375 MYA seed plants 380 MYA, gymnosperms dominant until 100 MYA flowering plants 130 MYA, currently dominant

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Phylum Rhyniophyta 380-425 MYA, earliest known vascular plants Seedless, leafless, dichotomously branched stems, terminal sporangia Minimal differentiation of roots/stems/lvs Cuticle, stomata, epidermis, cortex, photosynthetic stems Vascular tissue similar to hydroids in mosses Homosporous Isomorphic generations Marshes Cooksonia oldest known vascular plant

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Phylum Zosterophyllophyta 370-408 MYA Leafless, dichotomously branched stems Laterally borne kidney-shaped sporangia Aerial parts covered w/ cuticle and stomata Downward branch similar to root Grass-like appearance Homosporous Ancestor of lycophytes

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Phylum Trimerophytophyta 395-415 MYA Evolved from Rhyniophyta Larger, ↑ complexity/specialization Leafless, dichotomously branched Large vascular strand thus ↑ ht Homosporous Ancestor of pteridophytes and progymnosperms

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Phylum Lycopodiophyta 10-15 living genera, 1200 sp. Descendants of zosterophylls Trees w/ woody/secondary growth or herbs Possess microphylls (small lvs) 400 MYA divergence of 2 clades lycophytes – club mosses tree lycophytes dominant in Carboniferous euphllophytes – ferns, horsetails, seed plants

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Family Lycopodiaceae 15 genera, 400 sp. Club moss (Lycopodium sp.) Artic to tropics, evergreen Rhizome w/ roots and stems Spiral microphylls Homosporous Sporangia borne on sporophylls (fertile microphyll) some sporophylls non-photosynthetic = strobili conelike Bisexual gametes but cross fertilize 6 - 15 yrs for archegonia/anthredia mature Water required for fertilization - biflagellated sperm Independent sporophyte

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Family Selaginellaceae 1 genus, 750 sp. Tropics to deserts Selageniella – resurrection plant become dormant when dry SW

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Family Selaginellaceae Microphylls, sporophylls and strobili Ligule = small, scalelike outgrowth at base of sporophylls Heterosporous megasporangia borne by megasporophylls produce megaspores microsporangia borne by microsporophylls produce microspores mega- and microsporangia contained on single strobili Water necessary for fertilization (biflagellate sperm) Suspensor of embryo pushes embryo into gametophyte, which feeds off of gametophyte before becoming independent Gametophytes are unisexual growth w/i spores Nutritionally dependent sporophyte grows w/i gametophyte

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Family Isotaceae 1 genus (Isoetes), quillwort Sporophyte body underground stem w/ microphllys and roots Heterosporous w/ mega-/microsporophylls and spores Cambium produces 2º tissues w/ sieve elements/tracheids/ parenchyma Some obtain C from sediment, not atmosphere these lack stomata, have thick cuticle, minimal gas exchange w/ atmosphere, CAM Black-spored Quillwort

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Phylum Pterophyta 11,000 sp., mostly in tropics Diversity of form/habit/size, some epiphytic Now includes Sphenophyta (horsetails)

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Phylum Pterophyta Homosporous or heterosporous 2 types of sporangia eusporangia = multiple superficial initials (a.k.a. parent cells) involved in development of sporangia, results in inner and outer layers inner layer = irregular mass, gives rise to spore mother cell outer layer = sporangium wall

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Phylum Pterophyta leptosporangia = 1 superficial initial results in stalked sporangium w/ capsule containing nutritive tissue (tapetum) tapetum gives rise to annulus each sporangia contains annulus annulus = layer of cells that contracts to catapult spores inner tissue becomes spore mother cells (= 4 spores)

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Phylum Pterophyta 4 types of ferns O. Ophioglossales and Marattiales (eusporangiate ferns) O. Ficales (homosporous leptosporangiate ferns) O. Marsileales and Salviniales (heterosporous leptosporangiate ferns) O. Psilotales (reduced fern)