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Chapter 21 Vascular Plants Without Seeds (Early Vascular Plants (Groups…

- - - - Rhynia & Aglaophyton - addition of stomata and guard cells
      - Lyonophyton & Sciadophyton - gametophyte dominant, terminal gametangia instead of sporangia, stomata
      - Horneophyton - similar to hornwort with swollen stem base and same location of sporogenous tissue, stomata
      - Cooksonia - earliest rhyniophyte
      - Trimerophytes
        
        Megaphyll evolution from branch systems
        
        Megaphylls
        
        Monilophytes - ferns #
        
        Typical ferns - Leptosporangiatae - can be found in almost any habitat, all perennial and herbaceous, size from very small to as large as a small tree, sporophyte has a single axis and has true roots and megophyllous leaves, endarch siphonostele vascular system, most have leaves serve for photosynthesis and as sporophylls, most homosporous, spores germinate into a small gametophyte that bears both archegonia and and antheridia
        
        Psilotum - highly derived ferns that are the simplest of all vascular plants, dichotomous branching of upright stems, prostrate rhizomes, no roots or leaves. Gametophytes are small and covered with rhizoids, they live by absorbing nutrients from soil fungi
        
        Equisetophytes - sister clade of ferns
        
        Equisetum - only extant genus with 15 species, common name horsetails or scouring rushes, jointed stems with leaves at nodes, rhizomes, true roots
        
        Lignophytes - Woody plants
    - - Some groups with specialized sporangia, pseudomonopodial branching, enations that varied from small to proto-leaflike
        
        Evolution into lycophyte group
        
        Extinct genera
        
        Lepidodendron, Sigillaria & Stigmaria - had vascular cambium and secondary growth, but vascular cambium could not form new fusiform initials
        
        Drepanophycus & Baragwanthia - earliest lycophytes, large enations with a single strand of well-developed vascular tissue called microphylls
        
        Lepidostrobus & Lepidopholoios - megaspore developed into a megagametophyte, in some species the megaspore was retained in the sporophyll like a ovule and seed in seed plants
        
        Extant genera
        
        Lycopodium - common name ground pine or club moss, ~200 living species, all small herbs with prostrate rhizomes, true roots, short, upright branches, microphylls spirally on stems, no secondary growth, homosporous, gametophyte dominant
        
        Selaginella - heterosporous, megagametophyte develops inside megaspore wall, microgametophytes also develop in megaspore wall, have a ligule on the upper surface of leaves
        
        Isoetes & Stylites- Isoetes is a genus of ~60 small plants commonly called quillworts, have leaves and roots, leaves contain sporangia, have weak cambial growth, Stylites plants are very similar
        
        Phylloglossum
  - - - Origination theories
        
        Interpolation hypothesis - sporophyte came to exist when a zygote germinated mitotically, gradually evolved in complexity and entered the main life cycle
        
        Transformation theory - after dibiontic life cycle originated, two opposite groups diverged where one form was enlarged while the other was reduced
    - - Protostele - center is a solid mass of xylem with no pith, earliest form of vascular tissue
        
        Endarch prostele - protoxylem in the center and metaxylem on the outer edge of the xylem mass
        
        Exarch prostele - metaxylem in the center of the xylem mass and protoxylem on the edge in several groups by phloem
      - Siphonostele - pith present in center, later form of organization in ferns and seed plants