1Bryophytes, Pteridophytes &Adaptations of Land PlantsProfessor: Thomas CarlsonBio 1B Fall ’072LandPlants3Land Plants• 460 million years ago:– land plants evolved from aquatic green algae– the green algae were probably from fresh water• 400 million years ago:– first vascular tissue, stomata, & roots• 380 million years ago: first wood• 360 million years ago: first seeds• 260 million years ago: first vessels in vascularsystem• 125 million years ago: first flowers4Green Algae (Charophyta)(Figs 29.4, 29.7)progenitor to Green Land Plants• Green Land Plants– cellulose cell wall– chlorophyll a and b– starch storage product in chloroplast– embryo protected by tissue of parent plant– alternation of generations567Adaptations to Life on Land• Apical Meristems of Shoots & Roots (Fig 29.5)• Cuticle: waxy covering that retards desiccation(drying)• Stomata: developed for gas exchange• Pigments that protect plant against UV radiation• Land Plants Optimize Photosynthesis– CO2 from atmosphere is more available on land– LIGHT from sun is more available on land89Adaptations to Life on Land(Fig 29.5)• Thick spore walls that prevent desiccation &resist decay• Gametangia: enclose plant gametes & preventthem from drying– Archegonia: encloses eggs– Antheridia: encloses sperms• Embryos: young sporophytes contained withinprotective structure1011Adaptations to Life on Land• Vascular Tissue:Vascular tissue enables transport of water against gravityfrom tissues in contact with wet soil to tissues in contactwith air:– Hydroids (tiny channel through which water travels) inmosses (type of bryophyte)– Tracheids (specialized conducting cells) inpteridophytes & gymnosperms– Vessels (specialized conducting cells) in angiosperms– Lignin strengthens cell walls of vascular conductingxylem and provides rigid structural support so plantdoes not fall over in response to gravity or wind1213Bryophytes =Non-tracheophyte plants(Table 29.1, Figs 29.7, 29.8, 29.9, 29.10)• Earliest land plants• Most are only a few cm high or long• Grow in dense mats in moist habitats and requirewater for sperm to travel to eggs• Alternation of generations• Dominant haploid gametophyte• Sporophytes are dependent & attached togametophyte• Typically heterosporous with spores producingunisexual male or female gametophytes14Bryophytes =Non-tracheophyte plants• Liverworts (Marchantia) (Fig 29.9)– flat thallus with dichotomous branching• Hornworts (Fig 29.9)– stomata development• Mosses (Polytrichum, Funaria) (Fig 29.9)– apical cell division– hydroids: primitive vascular tissue– green leaf bearing structure is the gametophyte1516Bryophytes =Non-tracheophyte plants• Sphagnum moss (common name is peat moss)• Very abundant & widespread in wetland bogs innorthern latitudes• Peat: partially decomposed plant materialresulting from rapidly growing upper layers ofSphagnum that compress deeper lying layers (Fig29.10)• Sphagnum moss contains acidic compoundsthat are antiseptic & is used to treat– diaper rashes– athlete’s foot– to dress wounds17• Bryophytes/mosses (non-tracheophytes)– sporophyte is small and depends on the gametophytefor nutrition• Pteridophytes/ferns (seedless tracheophytes)(Figs 29.12, 29.14)– Sporophytes are much larger than gametophytes– Both sporophytes and gametophytes produce their ownfood through photosynthesis– Mature gametophyte lives independent of maturesporophyte1819Tracheophytes• Contain tracheids which are the principal waterconducting element of the xylem– water & mineral transport– rigid structural support• Dominant and independent sporophyte phase• Non-seed tracheophytes: pteridophytes• Seed containing tracheophytes:gymnosperms & angiosperms20Seedless Tracheophytes(Pteridophytes)(Table 29.1, Figs 29.7, 29.12, 29.14)• Rhyniopsida (only known from fossils)• Lycopods (Lycophyta): simple leaves in spiral• Horsetails (Anthrophyta) simple leaves in whorl– - Equisetum is genus name– - rich deposits of silicon in cell walls– - used to scour pans– - tea used as a diuretic• Whiskferns (Psilotophyta)• Ferns (Pterophyta)212223242526Seedless Tracheophytes(Pteridophytes)• Haploid & diploid generations independent atmaturity• Mature sporophyte dominant & independent• Reproduce by single celled spores• Homospory in terrestrial ferns• Small gametophytes, 1-2 cm long & short lived (with antheridium and archegonium on same gametophyte)• Require aqueous environment for motile, flagellatedsperm to fertilize2728Ferns (Pterophyta) (Figs 29.12, 29.14)• large complex leaves & branching vascular strand• roots, leaves, stems• require water for transfer of male gametes to femalegametes• sori: clusters of sporangia under leaf surfaces• moist terrestrial environments (most ferns)• Size: a few centimeters to over 10 meters (tree ferns)• some ferns are aquatic, epiphytic, or live on rocky cliffs29Frond = fern leaf (Fig 29.12)• Developing frond = crozier or fiddlehead(fiddleheads of some species consumed as delicacy)• Sporophyll = frond that produces spores• Sporangia = spore producing structures that areoften aggregated under the leaf into patches calledsori• Haploid spores develop into gametophytes303132333435363738394041424344454647484950515253Seedless Tracheophytes(Pteridophytes)• Homosporous: terrestrial pteridophytes• Heterosporous: aquatic ferns (e.g., Azolla &Marsilea)• Homospory: plants in which sporophyte producessingle type of spore that develops into a bisexualgametophyte with both male & female organs• Heterospory: plants in which sporophyte producestwo kinds of spores that develop into unisexualfemale or male gametophytes:– megaspores produce female megagametophytes– microspores produce male microgametophytes54Azolla (aquatic fern)Floating water fern with a symbioticrelationship with cyanobacteria, whichlive in leaf cavities• Cyanobacteria– Photosynthetic/oxygen producing– Fix nitrogen into ammonia which is converted by thefern into amino acids & other organic compounds• Azolla is commonly grown in rice paddies inAsia (especially Vietnam and Asia)• Grows very quickly & provides nitrogenfertilizer for the cultivation of rice that feedsmillions of people5556575859606162636465XXXDiploid DominantXXGametophytedependent onsporophyteX animals & windX mainly windPollinationXX GnetophytesVesselsXXXTracheidsXDouble fertilization &Triploid
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