Notes on Selaginella: Systematic Position, Plant body, Strobilus and more

Systematic Position of Selaginella
Division: Lycophyta
Class: Ligulopsida
Order: Selaginellales
Family: Selaginellaceae
Genus: Selaginella
Species: S.kraussiana (very common), S.monospora, S.adunca, S.picta
Occurrence:
Habit: grows in moist and shady hill sides
Epiphytic: S.oregana
Xerophytic: S.lepidophylla
Plant body
  • The plant body is the sporophyte, differentiated into root stem and leaves
  • Creeping or erect plant body
  • Stem: dichotomously branched later become monopodial
  • Leaves: small, simple, sessile, green, thin microphyllous leaves. Unbranched midrib
  • Function: photosynthesis
  • Roots: Adventitious roots, dichotomously branched arising from the stem
image
Other features:
  • Heterosporous nature.
  • Eusporangiate
  • Life cycle: Heteromorphic alternation of generation
  • Ligule and rhizophores present.
Ligule:
  • Small tongue shaped outgrowth or appendage present at the base of each young leaf on its adaxial or upper side.
  • At the bas of ligule, a sheath of elongated secretory cells are present called as glossopodium
Function: Not well known.
  • protective organ
  • Secretory organ that keeps sporangium and young leaf wet
Rhizophore are positively geotropic, long, cylindrical, leaf less colourless, prop like structures that produce tufts of adventitious roots at the free ends
 Rhizophore

  • It originates from the regions of dichotomy of the stem or points of branching.
Vegetative Reproduction
  • Fragmentation S.rupestris
  • Tubers: S. chrysocaulos
  • Resting buds: in aerial branches S. chrysocaulos
Strobilus: Spore producing structure
  • Selaginella is heterosporous and Eusporangiate: It bears two kinds of spores; microspores and megaspores produced inside microspoarngium and megasporangium on microsprophylls and megasporophylls respectively.
  • Spores are produced inside sporangia in the axils of sporophylls.
  • Sporophylls are organized into cones or strobilus
  • Strobilus consists of a central axis on which microsporophylls and megasporophylls are arranged.
  • The location of microsporangia and megasporangia varies between species
  • Dehiscence by vertical splitting from the upper end into two valves
Gametophyte or prothallus
  • Microspore are small in size and produced in large numbers inside microsporangium
  • Male gametophyte develops within the microspore wall and produces ~ 256 spirally coiled bi-flagellated antherozoids.
Selaginella Gametophyte
  • Megaspores are large in size, 1-4 numbers
  • Megaspores germinates within megasporangium forming female gemetophyte bearing archegonia.
  • Water is essential for fertilization
  • The young sporophyte remains attached to the megaspore for some time later falls to the ground and form roots and become independent

Heteromorphic alternation of generation
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