Lepidodendrales †

Scale Trees

Age: Devonian - Permian

Features
  • Ecology and Form
    • Arborescence in extinct taxa 
    • Inhabited late Paleozoic swamps
  • Stems (e.gLepidodendron, Sigillaria, Diaphorodendron)
    • Pseudo-bipolar growth
      • Root decays early in development
      • Early embryonic shoot splits with one "branch" becoming the "root" or rhizophore
    • Exarch primary growth
    • Unifacial (one-faced) cambium
      • Small amount of secondary xylem (wood)
      • No secondary phloem
        • Sugars from photosynthesis could not be transported to rhizophore
    • Large amount of bark (phellem) 
      • major support structure
  • Leaves (Lepidophylloides)
    • Microphylls or lycophylls
      • very long; up to 14" long
    • Spiral phyllotaxy shown in leaf scars on bark
  • Roots
    • No true roots
    • Rhizome-like stem called rhizophore (Stigmaria) acts like roots
    • Modified leaves acts like secondary roots to absorb water minerals
      • Rhizophore has rhizotaxis (pattern of root insertion) due to leaves growing in an apical fashion
  • Reproductive Structures
    • Sporangia in cones (Lepidosporobus)
    • Heterosporous
      • Megaspores and microspores
    • Endosporic development
      • Female gametophyte is not free-living
      • Seed-like
    • Possibly monocarpic (reproduce once and then die)
Systematics
Superkingdom Archaeplastida - plants + algal relatives
   Kingdom Plantae - "plants"
      Subkingdom Embryophyta - land plants
         Phylum Lycopodiophyta- club-mosses and their allies
            Class Lycopsida
               Order Lepidodendrales
                   Family Lepidodendraceae 
      • intrafoliar parichnos that extend below the leaf scar
      • dorsiventrally-flattened megaspore with distal dehiscence
                   Family Diaphorodendraceae 
      • medullated protostele
      • dorsiventrally-flattened megaspore with proximal dehiscence
                   Family Sigillariaceae 

Taxa
  • Diaphorodendron: 
  • Sigillaria: upright stem with bark
  • Lepidodendron: upright stem with bark
  • Lepidophylloides: leaves (microphylls) 
  • Stigmaria: root-like rhizophore (modified rhizome-like stem that anchors and absorbs water/minerals)
  • Lepidostrobophyllum: sporophyll (leaf protecting sporangia)
  • Lepidocarpon: female cone (contains megaspores) 
  • Cystosporites: megaspores, which will produce female gametophytes
  • Lepidostrobus: male cones (contains microspores) 
  • Lycospora: microspore, which will produce male gametophytes
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