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Evolution of Land Plants Prior to the origin and diversitication of green plants in the mid-Silurian (~450 mya), multicellular life was virtually entirely apapted to, and confined to, aquatic lifestyles Contintnenal Land Masses virtually unoccupied by multicellular organism – multicellular-based ecosystems constituted tremendous potential for adaptive radiation Terrestrial life in a gaseous medium required evolutionary solutions to structural, physiological and ecological challenges; Many of these innovations can be regarded as exaptations of pre-existing traits of green algae from which green plants diverged Artist’s rendering of Carboniferous forest in a tropical river delta. Most of the plants depicted here were nonseed tracheophytes 10 to 20 meters tall. In the distance, earl seed plants up to 40 meters tall towered over the forest. Kingdom Plantae is monophyletic assemblage, descended from Green algae Chlorophyll a and b are homogous in Chlorophyta, Charaphyta and Plantae Currently includes over 250,000 described species classified in 12 monophyletic phyla Most are terrestrial, some are secondarily aquatic Diversification in plants involved successive adaptive radiations following evolution of key innovations that increased efficiency in an gaseous (air) and solid (Earth) environment Major problems were posed by gravity and by water loss/availability -maintain body structure – resist gravity -obtain, transport and retain water -fertilize eggs and produce and protect embryos Major evolutionary innovations included Green algae of phylum Chlorophyta, such as Chara sp., are most likely ancestors of plants. Copyright BPS. -dimorphic body -waxy cuticle and stomata -vascular tissue; -jacketed sex organs; antheridia and archegonia -life history dominated by sporophyte generation -seeds embryo with nutritive tissue in protective covering -flowers; vehicles for pollination strategies Dense matt of mosses colonizes old lava in Iceland. Copyright BPS Leafy liverwort (Lophocolea bidentata), showing overlapping leaves andcreeping growth form. Copyright BPS. Leafy liverwort (Lophocolea bidentata), showing overlapping leaves and creeping growth form. Copyright BPS. Marchantia, a common liverwort. The sporophytes are born within the tissues of the umbrella shaped structures that arise from the surface of the flat, green, creeping gametophyte Hornwort sporophytes. Unlike other Bryophytes, hornwort sporophytes are photosynthetic Gametophytes of Sphagnum moss growing in a bog in central Newfoundland. Copyright BPS. Order Lycopodiales: club moss (Lycopodium annotinum); Denali National Park and Preserve, AK. Copyright BPS. Fern (Blechnum magellanicum) in rain forest of Chile's Patagonian coast. Copyright Alejandro Frid/BPS. Tree ferns (Dicksonia antarctica), in a forest of Eucalyptus regnans; Australia. Copyright BPS. Club Moss Big leaf maples hung with epiphytes, most of which are club mosses; Hoh Rain Forest, WA. Copyright BPS. Simple determinate inflorescence of shooting star (Dodecatheon meadia). Copyright J. Robert Stottlemyer/BPS. Family Arecaceae: desert fan palm (Washingtonia filifera); Colorado Desert, CA. Copyright Jon Mark Stewart/BPS. Family Pinaceae: Colorado blue spruce (Picea pungens). Copyright Pollock/BPS. Family Pinaceae: Pinus ponderosa, ponderosa pine, is widespread in the American West. Copyright Sources: Freeman (2002), Purves et al (2001) First extensive grassland Overview of the evolutionary history of plants Consider five intervals of evolutionary history, each defined by at least one major evolutionary innovation Archaefructus, an early flower First Flowering Plant Cones from Araucaria mirabilis, an early gymnsperm First nectar-drinking insects Carboniferous (lycopods, seed ferns, and horsetails abundant) First vessels Seed fern leaves 1st seeds 1st vascular plant leaves 1st wood 1st roots 1st vascular tissue 1st stomata 1st megafossils (small club mosses and other extinct groups 1st lycopod leave Fragment of plant cuticle Fossil frond of fern (Asterotheca arborescens); late Carboniferous. Copyright Barbara J. Miller/BPS. Fossil stem of oldest known lycopod genus (Bothrodendron minutifolium); late Devonian. LM. Copyright Phil Gates/BPS. Cells in fossil stem of Rhynia major (extinct Phylum Rhyniophyta); late Silurian and Devonian. LM. Copyright Phil Gates/BPS. Spores in fossil Rhynia major; late Silurian and Devonian. LM. Copyright Phil Gates/BPS Our current understanding of Plant phylogenetic relationships is based on analysis of both morphological and molecular characters •SSU rRNA and Rubisco •presence/absence of vascular tissue, leaves, seeds… •The broad picture of plant evolutionary relationships includes… •Divergenge of entire clade from green algae •indicates a single transition to land •indicates freshwater to land transition (because almost all modern Charopytans are freswater inhabitants) •All Plantae lineages; cellulose-based cell walls, chlorophyll a and b, starch as storage molecule in chloroplasts •Two of the three earliest lineages (nontracheophytes) lack water transport cells; mosses have have limited numbers of them Rubisco catalyzes a reaction in the CalvinBenson cycle of photosynthesis in which carbon from CO2 is added to a five-carbon chain. Our current understanding of Plant phylogenetic relationships is based on analysis of both morphological and molecular characters •SSU rRNA and Rubisco •presence/absence of vascular tissue, leaves, seeds… The broad picture of plant evolutionary relationships includes… •Divergenge of entire clade from green algae •All Plantae lineages; cellulose-based cell walls, chlorophyll a and b, starch as storage molecule in chloroplasts •Two of the three earliest lineages (nontracheophytes) lack water transport cells; mosses have have limited numbers of them •Seedless vascular plants (nonseed tracheophytes) have vascular tissue and leaves, but reproduce by making spores; no seeds Gymnosperms and Angiosperms have vascular tissue, they have complex leaves, and they produce seeds. Early lineages dependent on wet habitats and more recent ones not – adaptive radiations into mesic and xeric conditions Key Evolutionary Innovations and Trends in the Transition of Plants to Land -reducing water loss; cuticle and stomata -transporting water; vascular tissue and wood -transporting gametes and prtoecting embryos; pollination mechanisms and nutrititive, protective seeds Key evolutionary innovations and trends for capturing energy from sunlight -Photosynthetic Pathways C3 and C4 -Crassulacean acid metabolism -growth habits and life forms Nature 389, 33 - 39 (1997) © Macmillan Publishers Ltd. The origin and early evolution of plants on land PAUL KENRICK AND PETER R. CRANE the Swedish Museum of Natural History, Box 50007, S-10405, Stockholm, SwedenThe Field Museum, Roosevelt Road at Lake Shore Drive, Chicago, Illinois60605, Department of the Geophysical Sciences, University of Chicago, USA. The origin and early evolution of land plants in the mid-Palaeozoic era, between about 480 and 360 million years ago, was an important event in the history of life, with far-reaching consequences for the evolution of terrestrial organisms and global environments. A recent surge of interest, catalysed by palaeobotanical discoveries and advances in the systematics of living plants, provides a revised perspective on the evolution of early land plants and suggests new directions for future research. Figure 1 Morphological diversity among basal living land plants and potential land-plant sister groups. a,Coleochaete orbicularis (Charophyceae) gametophyte; magnification × 75 (photograph courtesy of L. E.Graham). b, Chara (Charophyoceae) gametophyte; magnification × 1.5 (photograph courtesy of M.Feist). c, Riccia (liverwort) gametophyte showing sporangia (black) embedded in the thallus; magnification× 5 (photograph courtesy of A. N. Drinnan). d, Anthoceros (hornwort) gametophyte showing nbranchedsporophytes; magnification × 2.5 (photograph courtesy of A. N. Drinnan). e, Mnium (moss) gametophyteshowing unbranched sporophytes with terminal sporangia (capsule); magnification × 4.5 (photographcourtesy of W. Burger). f, Huperzia (clubmoss) sporophyte with leaves showing sessile yellow sporangia;magnification × 0.8. g, Dicranopteris (fern) sporophyte showing leaves with circinate vernation;magnification × 0.08. h, Psilotum (whisk fern) sporophyte with reduced leaves and spherical synangia(three fused sporangia); magnification × 0.4. i, Equisetum (horsetail) sporophyte with whorled branches,reduced leaves, and a terminal cone; magnification × 0.4. j, Cycas (seed plant) sporophyte showing leavesand terminal cone with seeds; magnification × 0.05 (photograph courtesy of W. Burger). Figure 2 a, Longitudinal section of part of a silicified early fossil gametophyte (Kidstonophyton discoides from the Rhynie Chert). Antheridia (male sexual organs) are located on the upper surface of the branch; magnification × 3.4. b, Longitudinal section of antheridium of Lyonophyton rhyniensis from the Rhynie Chert; magnification × 40. c, Longitudinal section of archegonium (female sexual organ) of Langiophyton mackiei from the Rhynie Chert; magnification × 80. a–c are from the Remy Collection (slides 200, 90 and 330), Abteilung Paläobotanik, Westfälische Wilhelms-Universität, Münster, Germany (photographs courtesy of H. Hass and H. Kerp). d, Scanning electron micrograph of Tetrahedraletes medinensis showing a spore tetrad of possible liverwort affinity from the Late Ordovician (photograph courtesy of W. A. Taylor); magnification × 670. Figure 3 Sporophyte diversity in Early Devonian rhyniophyte fossils. a, Cooksonia pertoniiapiculispora: sporophyte (incomplete proximally) with terminal sporangium15; magnification × 15. b,Tortilicaulis offaeus: sporophyte (incomplete proximally) with terminal sporangium81; magnification × 40.c. Tortilicaulis offaeus: sporophyte (incomplete proximally) with terminal bifurcating sporangium81;magnification × 30. d, Transverse section of sporangium showing thick wall and central spore mass;magnification × 70. e, Details of epidermis at rim of sporangium; magnification × 45. f, Stomate with tworeniform guard cells (stippled); magnification × 120. Figure 5 Diversity of water-conducting cells (tracheids) in early land plants (median longitudinal sectionthrough cells, basal and proximal end wa. lls not shown; cells are 20–40 m diameter). a, Top,bryophyte hydroid; bottom, details of hydroid wall showing distribution of plasmodesmata-derivedmicropores (10–50 nm diameter; stipple)84. b, Top, S-type tracheid (fossil) of Rhyniopsida; bottom,details of S-type cell wall showing distribution of plasmodesmata-derived micropores (stipple) and'spongy' interior to thickenings19. c, Top, G-type tracheid (fossil) of basal extinct eutracheophytes, whichclosely resemble the tracheids of some living vascular plants; bottom, details of G-type cell wall showingpores distributed between thickenings19. d, Top, scalariform pitted P-type tracheid (fossil) typical oftrimerophyte grade plants (euphyllophytes); bottom, details of P-type cell wall showing pit chambers andsheet with pores that extends over pit apertures26.