Bio 144 Plant Diversity Lecture 6 PDF

BIOLOGY 144 6. Seedless vascular plants: horsetails and clubmosses PLANT DIVERSITY Lycophyta Equisetophyta Pterophyta Pterophyta  3. Phylum Equisetophyta (perdesterte) Equisetophyta has rich fossil record – antiquated relatives up to 300 milli...

BIOLOGY 144 6. Seedless vascular plants: horsetails and clubmosses PLANT DIVERSITY Lycophyta Equisetophyta Pterophyta Pterophyta  3. Phylum Equisetophyta (perdesterte) Equisetophyta has rich fossil record – antiquated relatives up to 300 million years old; some are trees Equisetum is the only surviving genus; includes 15 species branched or unbranched stems and branched perennial rhizomes true leaves are absent, but stem is the main site of photosynthesis present in most habitats across the world largest species up to 3 m hoog, most species are smaller (> 1 m)  stem divided into nodes and internodes articulation at the nodes formed by whorl of leaves fused into a bundle around the stems leaves brond, reduced, non-photosynthetic, only terminal tips free – stems photosynthesize stem branching pattern unique among vascular plants side branches do not develop from axillary buds above leaves, but from between the leaf bases internal structure of stem unique and compex vascular bundles arranged separately in an eustele arrangement along internodes bundels fuse at the nodes to vorm a siphonostele arrangement  internodes characterized by presence of a central and periferal rings of air channels and epidermal ridges central channel replaced by pith at the nodes  Equisetum is homosporous sporangia confined to terminal strobilus on vegetative branches or to fertile branches sporangia not borne on leaves (sporophylls), but on flattened branches called sporangiophores each sporangiophore bears finger-shaped sporangia strobili elongate to separate the sporangia when spores are ready to be released  Spores have extra hygroscopic layer that unwraps to form 4 ribbons Ribbons entangle allow gametophytes to germinate in close proximity Increase chances of fertilization  gametophytes look like pincushions and can photosynthesize basal zone with rhizoids and branched (pincushion) zone with flattened green lobes archegonia borne basally, antheridia terminally on lobes after fertilization the roots of the new sporophyte grows through the gametophyte and establish  sporophyte becomes independent many sporophytes develop per gametophyte 4. Phylum Lycophyta superficially similar to mosses, but only very distantly related true vascular plants – internal structure and reproduction common in humid and tropical areas across globe large proportion of club moss diversity went extinct ca. 270 million years ago only 1000 extant species, divided into 4 genera (most speciose and common: Lycopodium and Selaginella) sporophyte has short, branched stems with very small sessile leaves (microphylls) roots emerge adventitiously from perennial rhizome, which often grows from a central point  Lycopodium Selaginella  sporangia borne singly on topmost surface of fertile leaves known as sporophylls sporophylls distributed among sterile leaves sometimes aggregated at tips of branches to form strobili Two types of spore production in Lycophyta:  homosporous in Lycopodium  Gametophyte short-lived (photosynthetic) or long-lived (saprophytic)  Hermaphroditic, but self-fertilization scarce  antheridia mature before archegonia  1 zygote develops on short-lived gametophytes  Long-lived gametophytes produce many zygotes Sporangium Sporofille Sentrale as Derived traits in Selaginella 1. Spore production heterosporous in Selaginella Micro- and macrospores in micro- and macrosporangia produced on micro- and macrosporophylls Respectively viewed as male and female SPORES Separate male and female gametophytes 2. Gametophytes shrink to the extent that they care retained within spore walls macrospores divide mitotically within spore  multicellular female gametophyte grows and develops until gametophyte breaks through the spore wall to expose the archegonia 3. Cones contain both micro- and macrosporophylls  male gametophytes also formed within microspores; reduced and often only a single antheridium produced  antheridium breaks through microspore wall just before gamete maturation and release male gametes, which fertilize the egg cells to form zygote  zygote germinates and forms embryo with a foot region and embryonic root, stem and leaf Homospory Heterospory  Economic importance of seedless vascular plants Often used as fossil markers in sedimentary rock for presence of coal/oil Pterophyta very important to horticulture/cut flower industry Chemicals in Pterophyta used in traditional medicines Early pioneers used Equisetum stems as pot scourers Lycopodium spores – ignition source in early torches/guns Lycopodium alkaloids still used industrially Green Bryo SVP Gymno Angio algae Dominant 2N Vascular tissue Life on land Organs N 2N Pterophyta Equisetophyta Lycophyta