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2/23/11 2/23/11 What is a land plant? Embryophytes Any photosynthetic eukaryote that can survive and sexually reproduce on land All land plants are embryophytes (= embryo bearing plants) • Defined by a true alternation of generations with multicellular diploid and haploid phases, and the two phases remain physically connected. Notes available from website • • Diversity and evolution of major groups of land plants Gametophyte (haploid) stage Sporophyte produces sporangia which make haploid spores Gametophyte produces haploid gametes, which unite in the archegonium of the gametophyte Sporophyte (diploid) stage Robin Allaby (http://www2.warwick.ac.uk/fac/sci/whri/research/archaeobotany/) A brief history of time Notes available from website Overview Evidence of first land plants: 480-360 Mya • cuticles & stomata • archegonium & sporopollenin walled spores • vascular systems • Origin of land plants • Evolutionary history of land plants – Major morphological innovations: alternation of generations cuticles and stomata vascular tissues heterospory seeds leaves flowers • Resultant phylogenetic tree of plants • Some evolutionary trends convergence polyploidy genome expansion (417) (440) 1 cm bar 545 495 Cambrian Ordovician • 417 Silurian 354 Devonian 292 Carboniferous 251 Permian 202 Triassic Jurassic 142 65 Cretaceous 24 Palaeogene 458 1.8 Neogene Q Vascular tissues: evolution of xylem and phloem What is a land plant? Invasion of land was really an invasion of the air • dessication and support are the principal problems • adaptation to dessication requires : a cuticle (and consequentially stomata) spores and seeds (ultimately) vascular tissue (when plants are above a certain size) 440 (495) Circa 415 Mya Cooksonia paranensis (Gerrienne et al 2006) Heterospory embryophytes Any photosynthetic eukaryote that can survive and sexually reproduce on land better adapted for moist environments than tracheophytes amplification of gametophyte poikilohydric amplification of one stage must reduce the other better adapted for dry environments than bryophytes unisexual gametophytes, manifest as heterosporous amplification of sporophyte 397 - 391 Mya (Eifelian) homoihydric 1 non vascular vascular (bryophytes) (tracheophytes) mosses, liverworts and hornworts ferns, lycopods, horsetails, and seed plants See Proctor 2007 phyletic trend for taller sporophytes, bisexual gametophytes, homosporous plants that release spores = pteridophytes (fern like - includes lycopods (L), Horsetails (H) and Ferns (F)) 2 2/23/11 Heterospory 2/23/11 Heterospory The late arrival of leaves: 360 Mya!! (end of Devonian) Pollen tubes by early Carboniferous • Seems odd - reduces the chances of fertilization by separating egg and sperm. Cannot be good in a harsh environment, this is a cost. • Once separated, makes sense to increase energy investment in the “female” gametophyte which must support the sporophyte, and maximize chances of successful fertilization by making male spore numerous, (and consequently small). • Gives rise to out-crossing. Perhaps this is the advantage (?). • That it is an advantage is proven by the convergence on the habit - possibly as many as 11 times! (Bateman & DiMichele 1994). homospory heterospory Leaf evolution associated with falling CO2 levels (first plants evolved in a CO2 rich atmosphere) (Rothwell 1972) The logical progression of heterospory e.g. Barinophyton citrulliforme e.g. Chaleuria cirrosa e.g. Cystosporites devonicus Seed habit - the next step after heterospory (Beerling 2005) A snapshot of the Carboniferous • retain megaspore in megasporangium • reduce functional megaspores to 1 • retain megagametophyte (elimating requirement for external water for fertilization) • modification of megasporangia to receive microspores • modification of microspores to enable them to deliver sperm cells to eggs (ie pollen tube) • integument develops around megasporangia (later) Lycopod trees (Lepidodendron) Angiosperms appear 144 Mya (early Cretaceous) Equisetoid trees (Calamites) e.g. Archaeopteris & Selaginella increasing investment in megaspore causes reduction in megaspore number all seed plants = spermatophytes first seed plants = gymnosperms (naked seeds) Asteropollis sp. Pollen (Laurales) (Friis et al 2005) Oldest seed plant 385 Mya (Mid Devonian) Basic Gymnosperm architecture Evolution of Angiosperms Explosion in Angiosperm speciesGnetales is gymnosperm group closest to flowering plants salpinx • Angio = container - megasporangium (and integuments) enclosed in carpel. • Flower structure (a determinate shoot built from leaves). • 2 integuments not one (as in gymnosperms). • Double fertilization (resulting in triploid endosperm). • Xylem structure (vessel members and sieve tubes). • Other features to such as endopolyploidy ability (weed technology!), vegetative reproductive ability (weed technology!). • Very versatile - numerous floral strategies possible - a single mutation can result in sexual isolation and new species formation. • Introduction of animal based pollination strategies. integument + megasporangium uncovered megasporangium Angiosperms 220 000 species Bryophytes 22 400 species Pteridophytes 9 000 species Gymnosperms 750 species Fabaceae alone have 14000 species Also only land plant group to reinvade the sea (Zostera sp.) Integument does not fully enclose ovule Runcaria heinzelinii (Gerrienne et al 2004) 3 4 2/23/11 The diversification of angiosperms: Darwin’s abominable mystery Oldest flower fossils circa 125 Mya. 2/23/11 Evolutionary Trends: convergence (on tree habit) Evolutionary Trends: convergence (on cactus habit) Evolutionary trends: polyploidy Evolutionary trends: genome obesity • The rapid appearance of so many species of angiosperm was a problem for Darwin’s theory • In his version of events, evolution proceeds gradually, selecting minute changes • Saltation was an opposing view point – gives more emphasis to mutation (internally driven) than Natural Selection (externally driven) • Darwin discovered the reason, and founded ‘pollination biology’ Water lily (Nymphaeales) (Friis et al 2001) Angiosperms diversified because of floral morphology and pollinator co-evolution Floral evolution – protection to attraction Bisexual flowers Nectar reward, bees, predominate birds, moths, bats wind pollination First pollinators: beetles in small inconspicuous flowers Unisexual flowers predominate Blanc and Wolfe 2004 Friis et al 2006 basal buttercups, poppies grapes cactus Docks, rhubarb & sorrels witch hazel, stone crops mistletoe water lillies pepper (spice) magnolia basal complex: primitive dicots bay laurel geraniums Oldest tricolpate pollen 120 Mya basal core Obesity in the Liliales Fritillaria (Liliales) 127 000 Mb wood sorrel beans, peas, acacia Large cells, slow replication - good for bulbs roses, apples cucumber, melons &pumpkins monocots Oaks, birch, beech evening primrose Cabbages, Arabidopsis asparagus Arabidopsis (Brassicales) 157 Mb cotton, lime trees Lillies, daffodils etc oranges, lemons 30 Mya CO2 levels crashed: C4 metabolism evolved 62 times independently!! 26 in monocots and 36 in eudicots Angiosperm Phylogeny basal yams dogwood asterids heather, rhododendron, primrose Small cells, fast replication good for weed habit palms pineapples/air plants Endangered species? rosids Euphorbia, willow peace lillies Based on DNA sequences such as rbcL, matK, nadh, atpB, 18S rDNA Leitch et al 2005 Potato, tomoto, deadly nightshade coffee Mint, basil, rosemary, thyme etc., olives reeds and rushes grasses ginger, bird of paradise plants Tricolpate Angiosperms Why is there an over-representation of large genomes in the plant Red List? holly carrots, parsley. fennel honeysuckle, elder daisy, asters, thistles, bellflowers Vinogradov 2003, but read also Cavalier-Smith 2005 5 6 2/23/11 Suggested reading Crane PR, Friis EM, Pedersen KR (1995) The origin and early diversification of angiosperms. Nature 374: 27-33. Friis EM, Pederson KR, Crane PR (2005) When the earth started blooming: insights from the fossil record. Current Opinion in Plant Biology 8:5-12. Judd WS, Campbell CS, Kellogg EA, Stevens PF (1999). Plant Systematics: A Phylogenetic Approach. Sinauer Associates, Sunderland, Massachusetts. Kenrick P and Crane PR (1997) The origin and early evolution of plants Cavalier-Smith T (2004) Only six kingdoms of life. Proceedings of the on land. Nature 389:33-39. Royal Society of London Series B. 271:1251-1262. Niklas K (1997) The evolutionary biology of plants. University of Friis EM, Pederson KR, Crane PR (2001) Fossil evidence of water Chicago Press, Chicago. lilies (Nymphaeales) in the early cretaceous. Nature 410: 357-360. Friis et al 2006 Cretaceous angiosperm flowers: Innovation and evolution in plant reproduction. Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2006) 251–293 Other source material Friis et al 2010 Diversity in obscurity: fossil flowers and the early Bateman RM and DiMichele WA (1994) Heterospory: The most history of angiosperms. Phil. Trans. R. Soc. B 2010 365, 369-382 iterative key innovation in the evolutionary history of the plant Gerrienne P, Meyer-Berthaud B, Fairon-Demaret M, Streel M, kingdom. Biological Reviews of the Cambridge Philosophical Society Steemans P (2004) Runcaria, a Middle Devonian Seed Plant Precursor. 69:345-417. Science 306:856-858. Beerling DJ (2005. Leaf Evolution: Gases, Genes and Geochemistry. Gerrienne P et al. (2006) An exceptional specimen of the early land Annals of Botany 96:345-352. plant Cooksonia paranensis, and a hypothesis on the life cycle of the Blanc G, Wolfe KH (2004) Widespread paleopolyploidy in mode plant earliest eutracheophytes. Review of Palaeontology and Palynology species inferred from age distributions of duplicate genes. The Plant 142:123-130. Cell 16:1667-1678. Leitch IJ, Soltis DE, Soltis PS, Bennett MD (2005) Evolution of DNA Cavalier-Smith T (2005) Economy, sped and size matter: evolutionary amounts across land plants (Embryophyta). Annals of Botany forces driving nuclear genome miniaturization and expansion. Annals 95:207-217. of Botany 95:147-175. Proctor M (2007) Ferns, evolution, scale and intellectual impedimenta. New Phytologist 176:504-506. Rothwell GW (1972) Evidence of Pollen Tubes in Palaeozoic Pteridosperms. Science 175:772-774. Vinogradov AE (2003) Selfish DNA is maladaptive: evidence from the plant Red List. Trends in Genetics 19:609-614. 7