Monilophytes Fabulous Ferns The Monilophyte Lineage From Pryer et al. 2001 Leptosporangiate ferns Monilophytes Equisetaceae Eusporangiate ferns Psilotaceae Seed plants Lycophytes 1 Megaphylls Micro- vs. Mega-phyll Evolution • Leaf gap • Microphyll: single, • More than 1 branched vein unbranched vein with no leaf gap (left side) • Telome theory of megaphyll • Megaphyll: Vein evolution branching multiple times with a leaf gap (right side) • Review microphyll evolution from Lycophyte lecture Telome Theory of Megaphyll Eusporangium Evolution • Leaves (megaphylls) of arthrophytes, ferns & seed plants evolved from branch systems (telomes) by overtopping, planation & webbing Found in most plant lineages 2 Leptosporangium Eusporangium Leptosporangium • Relatively large • Relatively small • Thick-walled • Thin-walled (1 cell- (several cell-layers) layer thick) • Many spores (100s- • (Usually) 64 spores 1,000s) • No specialized • Dehisce via annulus dehiscence mechanism • Stalked • No stalk • Form from just 1 • Form from several initial cell initial cells Only in the “true ferns,” Polypodiophyta Location of Vascular Tissue The Stele • Evolutionary progression in complexity & • Arrangement (pattern) of vascular tissue location of vascular tissue (esp. stems) • Root & stem morphology usually different • Related to megaphyll development from each other – Large, numerous leaf traces = many large leaf gaps – How we can tell a rhizome is a modified stem, not • Location of stele = equilibrium between a root location of strengthening & conducting cells • Useful for distinguishing between different • Ideal location for strengthening tissue is just taxonomic groups beneath the surface of a cylindrical structure • Roots, which do not produce leaves, have at the center of the axis the most simple stelar types & the stele is in – Least likely to break when stems are bent by wind the center of the axis – Mostly an Actinostele 3 Stele Types: Protostele Stele Types: Siphonosteles xylem phloem xylem phloem • Simplest type of stele • Xylem & phloem form • Solid core of xylem concentric cylinders surrounded by a cylinder of around central pith phloem cortex • Ectophloic Osmunda • 3 general variations siphonostele: phloem pith • Haplostele: solid cylinder restricted to outer of xylem surface of xylem • Actinostele: radiating cog- Psilotum • Amphiphloic like ridges of xylem siphonostele • Plectostele: cylindrical (solenostele): phloem xylem core with masses of phloem interspersed within found both external & internal to xylem Fern stem Lycopodium Siphonostele Types Psilotophyta: Psilotum • Fault of leaves! – Don’t blame me Psilotophyta • Dictyostele: stele appears Psilotopsida as discrete strands or Psilotales bundles in cross section Psilotaceae Psilotum • Eustele: discrete strands, Tmesipteris xylem inner & phloem outer (dicots) • Atactostele: bundles scattered, xylem/phloem random facing – Monocots 4 Psilophyta Sporophyte Morphology • Until recently, though to be most primitive, • Naked stems extant lineage of vascular plants • Dichotomous branching • 2 genera • Rhizomes & rhizoids – Psilotum (pantropical) – No true leaves or roots – Tmesipteris (New Zealand) • Homosporous – Enations • Cultivated in Japan for 400-500 years as an • Similar to Rhyniophytes, but: ornamental – Enations (leaf-like flaps of tissue) • Whiskferns – Sporangia axillary (not terminal) – Sporangia fused into synangium Synangium Gametophytes • 3 fused sporangia (in Psilotum) • Small • In axils of enations (axillary) • Subterranean • Lack chlorophyll – Mycotrophic – Depend on fungal partners for nutrition 5 Psilotum Stems Primitive Lineage? • Many believe that Psilotum (& Tmesipteris) closest living relatives to Rhyniophytes. • BUT there are alternative hypotheses • Psilotophyta are highly modified group of ferns which have lost many fern-like characters Protostele (Actinostele) – Why? Large fossil gap; gametophyte similarities • Chemical & morphological features suggest affinity with “eusporangiate” Tmesipteris Ophioglossophyta Ophioglossophyta • Similar to Psilotum, but with leaf-like Ophioglossopsida structures Ophioglossales Ophioglossaceae • Enations or flattened stem? Botrychium Ophioglossum – Vascular tissue (rules against enation) Botrychium • Only 2 sporangia in synangium Ophioglossum 6 Ophioglossophyta The Players • Dimorphic fronds • Ophioglossum – Sporangia borne on fertile fronds – Adder’s-tongue ferns – Other segment is flattened & vegetative • Ophioglossum reticulatum has largest • Leaves are megaphylls known chromosome # (2n = 1,260!) • True roots – 84-ploid! • Homosporous – Haplopappus gracilis = lowest #, 2n = 4 • Gametophytes • Botrychium – Subterranean – Grape ferns; rattlesnake ferns – Lack chlorophyll – Mycotrophic Equisetophyta: Equisetum Equisetum Equisetophyta • Horsetails, scouring rushes Equisetopsida • Near-cosmopolitan Equisetales • Many fossil taxa Equisetaceae – Up to large trees Equisetum • Dates back to Triassic • Toxins include nicotine & thiaminase (breaks down thiamine) • May help with Alzheimer’s 7 Equisetum Stem Equisetum Stem • Jointed at nodes • 3 series of canals – Point of • Central (inner) attachment for – Aeration leaves & lateral • Carinal (middle) branches) – Associated with • Ridged (or ribbed) xylem & phloem • Accumulate silica – Opposite ridges in epidermis – Aids conduction • Vallecular (outer) • Photosynthetic – Alternate with – Leaves reduced ridges; function? Strobilus & Sporangiophore Spores • Elaters • Sporangia in strobilus – Modifications of outer • But in sporangiophores spore wall – Stem tissue, not • Dispersal sporophylls – Uncurl when dry – Peltate (umbrella-shaped) – Coiled when wet • Homosporous 8 Gametophyte Pteridophyta: “True” Ferns Polypodium • Photosynthetic • Unisexual – but plant homosporous! • Sex due to environmental cues, e.g., light intensity, quality (e.g., red light) • Some female gametophytes exude a chemical that turns neighboring ones male Phylogenetically Speaking Leptosporangiate Fern Taxonomy Polypodiophyta Polypodiopsida Polypodiales Polypodiaceae sensu lato Many genera; Various families (we’ll put them just in this one for now) Osmundaceae Osmunda Marsileaceae Marsilea Azolla Salvinia 9 Polypodiophyta General Morphology • Date to Devonian (like lycophytes & • Leptosporangiate eusporangiate Monilophytes) • Dictyostele • Abundant in Carboniferous (Pennsylvanian) • Leaves simple to compound • Modern fern genera date back to Tertiary & – Very variable across fern groups Cretaceous (not as old as extant lycophyte genera) – Megaphylls • Largest group of extant cryptogams (> • Circinate vernation 12,000 spp.) • Sporophyte dominant • Morphologically diverse – Free-living • Variety of habitats – Still require water for fertilization Circinate vernation Reproductive Morphology • Distinctive uncoiling of young leaves • Mostly homosporous – Also in cycads (convergence) • Sporophylls = megaphylls anatomically • Fiddleheads (or croziers) • Sporangia mostly in sori – Prior to uncoiling – Underside of leaves – That brown stuff that most people think is fungus or dirt 10 Fern Sporangia Exindusiate • Sorus: clusters of sporangia • Indusium: covering of sorus E.g., Phymatosorum • Annulus: specialized Indusium completely lacking dehiscence mechanism – Ring of thickened cells – Contract sharply when dry – Scatter spores E.g., Platysereus Exindusiate Peltate Sorus Reniform Sorus Reniform: kidney-shaped Peltate indusium E.g., Cyrtonium Peltate: umbrella-shaped E.g., Nephrolepis 11 False Indusium Gametophyte • Prothallus generally heart-shaped • Dorso-ventrally flattened False indusium E.g., Adiantium False indusium Pteridophyte Life Cycle OK, So Where Are We? Finished with these ones 12 Osmundaceae Osmundaceae • Basal lineage – Lack of sorus – Primitive annulus – Molecular data • E.g., royal fern, cinnamon fern • Dimorphic leaves – Separate fertile/sterile (cinnamon) Osmunda regalis (royal fern) – Both on one (royal) Osmunda cinnamomea (cinnamon fern) Heterosporous Water Ferns Marsileaceae • ONLY heterosporous “true” fern lineage • Water clovers – Marsileaceae & Salviniaceae (sister groups) • Cosmopolitan in warm temperate & • Not particularly fern-like to look at tropical areas • Sporocarps: specialized adaptations to living in water – Modified sporophylls with tightly clustered sori; sporophyll fronds are hardened – Morphology varies across groups Marsilea 13 Marsilea Sporocarp Sporocarps: Sorophore • Paired at sterile leaf base • Sorophore: gelatinous backbone • Burst when hydrated – Swells when hydrated • Each sorus with micro- & mega – Sporangia attached sporangia Sorophore • Can keep spores viable up to 100 years – Adaptations for growth in arid Sporangium regions? • Dispersed by waterfowl • Sporangia lacking annulus Sporocarp (burst) Sporocarps Spores & Gametophytes Salviniaceae • Megasporangia with just 1 megaspore • Salvinia – Megagametophyte with 1 archegonium – Floating ferns • Microsporangia with 16-64 microspores – Microspores burst as sperm released • Gametophytes minute, endosporic • Azolla – Mosquito ferns 14 Salvinia Salvinia molesta • Rootless • Giant Salvinia, from SE Brazil • 3 leaves • WORLDWIDE NOXIOUS WEED! – 2 floating, leaf-like – 1 pendant, root-like • Produce sporocarps Salvinia molesta • Aggressive weed with wide ecological tolerance • Very rapid growth • A single plant has been described to cover 40 square miles in 3 months! • Rapidly expanding populations can overgrow & replace native plants • Resulting dense surface cover prevents light Azolla & atmospheric oxygen from entering water • Decomposing material drops to bottom, consuming dissolved oxygen needed by fish & other aquatic life 15 Azolla: Mosquito Ferns • 1 leaf with 2 lobes • Upper lobe houses Anabaena – Filamentous blue-green alga – Fixes atmospheric nitrogen • Was important in past rice crops – Fertilizer for rice plants – Still used in many places for same reason 16.