Luscious Primitive Vascular PlantsLycophytes Aglaophyton Primitive Vascular Plants Early Life Cycles• Small & simple in structure • Early vascular plants had• Sporophyte a dichotomously branching alternation of more or less similar generations stem – Sporophyte & – 1-2” high gametophyte (which was – Sporangia terminal also branched) ~ same – No leaves or roots size• Did not produce true tracheids in xylem • Compared to bryophytes, both generations initially – Used turgor pressure to remain upright elaborate• Tracheids then evolved, giving rise to tracheophytes Geological Time Scale The Rhynie Chert & Its Flora Rhynie Chert • Found 1912, Rhynie, Scotland • ~396 MYA • Extremely important for our understanding of early plants, including vascular plants http://www.uni-muenster.de/GeoPalaeontologie/Palaeo/Palbot/erhynie.htmlRhynie Chert Discoveries AglaophytonCyanobacteria: Algae s.l.: • Fossil taxon• Archaeothrix contexta • Mackiella rotundata• Archaeothrix oscillatoriformis • Palaeonitella cranii • Aglaophyton best-known taxon from• Kidstoniella fritschii • Rhynchertia punctata Rhynie Chert• Langiella scourfeldii Tracheophytes (Sporophytes):• Rhyniella vermiformis • Aglaophyton major – New studies have shown that the• Rhyniococcus uniformis • Asteroxylon mackiei conducting cells of Aglaophyton major areFungi: • Horneophyton lignieri strongly reminiscent of those of certain• Allomyces sp. • Nothia aphylla mosses• Glomites rhyniensis • Rhynia gwynne-vaughanii• Krispiromyces discoides • Trichopherophyton teuchansii – Some authors, therefore, do not regard• Milleromyces rhyniensis • Ventarura lyonii Aglaophyton as a real vascular plant• Palaeoblastocladia milleri Tracheophytes (Gametophytes):• Palaeomyces agglomerata • Langiophyton mackiei• Palaeomyces asteroxyli • Lyonophyton rhyniensis• Palaeomyces gordonii • Kidstonophyton discoides• Palaeomyces horneae • Still undescribed female gametophyte• Palaeomyces simpsonii• Palaeomyces simpsonii of Aglaophyton major• Several Chytridiomycetes • Still undescribed female and male• Ascomycetes gametophytes of Rhynia gwynne- Various other undescribed fungi vaughaniiLichens: • Still undescribed male gametophyte of• Winfrenatia reticulata Horneophyton lignieri• Nematophytes:• Nematophyton taitii• Nematoplexus rhyniensis Rhynia Asteroxylon • Asteroxylon mackiei, one of the earliest lycopods, is the only plant from the Rhynie Chert which had already small leaf-like structures – Lacked a vein • Central stele = star-shaped xylem surrounded by phloem (actinostele) • Resulted in a much greater plant stability • Comparatively complex architecture Asteroxylon Asteroxylon• Up to 40 cm high • Rhizome formed repeatedly bifurcating root-• Leaves up to 5 like organs up to 20 cm deep mm long – Not true roots, calyptra missing (cap-like structure• Reniform on root tip) sporangia on • Leaves considerably increased photosynthetic short stalks in surface leaf axils • Better able to regulate humidity – Keep dew drops between leaves – Better water regulation than other Rhynie Chert plants – Stomatal density of Asteroxylon is about 10X more than Aglaophyton – Unlike other Rhynie Chert plants, could likely survive in temporarily drier environments Let’s walk through the phylogeny ... Phylogenetic Context AnthoceroHphepytaatophBytrayopLhyyctaopodiopPhoyltyapodiophGytyamnospermAsngiosperms Cooksonia CharalesLycophytes Sporophyte or Gametophyte? Selaginella • Bryophytes – dominant gametophyte(Resurrection Plant) generation Isoëtes • Everything above them on the(Quillwort) phylogeny – dominant sporophyte Heterosporous • Gametophyte becomes successively reduced in size as we go along all the way up to angiosperms Lycopodium (Club Mosses) Homosporous Shared Lycophyte Characters Microphylls • Contain true stems, roots & leaves • Microphyll-type leaves • Leaves densely spirally arranged • Stems/ & roots often have dichotomous branching • Sporangia borne on leaves – “Sporophylls” • Sperm biflagellateEnation Theory of Microphyll Origin Extant Lycophyte Taxonomy enation microphyll LycopodiophytaVascular tissue Lycopodiopsida Lycopodiales• Remember Asteroxylon? Lycopodiaceae Selaginellaceae – Leaves without veins? Isoëtaceae – Enations! Lycopodiophyta Geological Time Scale• An ancient group Some extant• First fossils ~ 400 MYA (lower Devonian) lycophytes• Some extant genera known all the way Rhynie Chert (Includes first back to ~300 MYA (Pennsylvanian epoch lycophytes) of Carboniferous)• Today, a very small group, but once a dominant life form Lycopodiophyta Lycopodiaceae• The major contributor to coal deposits of • Clubmoss, ground pine, running cedar Carboniferous period [“Fossil Fuels”] • Fossils date back to Pennsylvanian (300• They were largest during this period (345- MYA) 290 MYA), dominating coastal swamps of • Homosporous & leaves non-ligulate tropical lowlands – Distinguish it from rest of order• Some (e.g., Lepidodendrales) were > 40 m high & 2 m diam., & dominated forests • Strobilus = terminal cluster of sporophylls• Majority of fossils from this time period – Some spp. lack strobili; sporophylls elsewhere from this group • Sporangia kidney-shaped, opening by a transverse slit; solitary in leaf axils or borne on leaf bases Lycopodium Sporangia Lycopodium Strobilus longitudinal slit • Note all spores are the same size • Contrast this with heterosporous plants HomosporousHomosporous Life Cycle Gametophyte • Epiterrestrial or subterranean • ~0.5” long • Bisexual antheridia archegonia Archegonia Spermatozoids Economics Heterosporous Lycophytes• Christmas garlands/wreaths • Selaginellaceae & Isoëtaceae• Oily, highly flammable compounds in • Produce 2 types of spores spore wall – Microspores (“male”) – Megaspores (“female”) – Magicians/sorcerers in Middle Ages (flash of light) • Microspores develop into microgametophytes – The 'flash' of old-time photography – Early (experimental) photocopiers – Produce antheridia & sperm – Industrial lubricants – Formerly prevention of rubber cohesion in • Megaspores develop into megagametophytes condoms & surgical gloves – Produce archegonia & eggs• Used to count Avogadro’s Number in chemistry lab Heterospory Heterosporous Lycophytes• Note the 2 different spore sizes • Ligulate leaves• Microspores are much smaller than – Leaves with a small flap of tissue at megaspores base Selaginella ligule Isoëtes liguleSelaginella strobilus Endosporic Gametophytes Selaginellaceae: Selaginella• Mega- and microspores produce endosporic gametophytes in the heterosporous lycophytes• Gametophyte produces wholly within spore wall (until mature) Isoëtes megagametophyteSelaginella microgametophyte Selaginellaceae Selaginella Sporangia• 1 genus (Selaginella) • Both sporophyll-types still microphylls anatomically – c. 750 spp. (38 in FNA) • Megaspores produced in megasporaniga• Most moist tropics (megasporophyll) – But many adapted to xeric habitats • Microspores produced in microsporangia (microsporophyll)• Leaves small (< 2 cm long)• Sporangia usually in strobili• Vegetatively similar to Lycopodium Megagametophyte Resurrection Plant• Endosporic • Adaptation to xeric environments – Bursting out when mature – Dormancy – Come back when conditions favorable• Anchored by rhizoids Archegoniawww.uvm.edu/~dbarring/selagfemgam.jpg Selaginella lepydophylla Heterosporous Life Cycle Isoëtaceae: Isoëtes sporangium Isoëtes: Quillworts Isoëtes• 2 genera in family, but we’ll look at Isoëtes • Stem – short, corm-like, (150 spp.; 24 spp. in FNA) 2(-4) lobed• Cosmopolitan, except for Pacific islands • Shoot & root apices• Fossils similar to Isoëtes as far back as the sunken Triassic (213-248 MYA) • Dichotomously branched – Some with leaves 1 m long! NB. Still microphylls• Usually aquatic or marshy-areas• Similar looking to grasses & rushes – Often overlooked• Leaves - elongated microphylls (up to 1 ft [30 cm], but can be as small as several centimeters)
