Lycopods of Pennsylvanian age coals: Polysporia

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Abstract
Permineralized specimens of Polysporia are described from coal balls of 3 Middle Pennsylvanian age coals of the Illinois Basin [USA]. Identification is based on the presence of Endosporites microspores and Valvisporites megaspores along with sporangial fragments in the axils of leaves interpreted as sporophylls. The shoots exhibit alternating fertile and vegetative zones. Vegetative leaves are larger than sporophylls which are often desiccated and folded back against the stem surface; a short zone of transitional sterile leaves is found between vegetative and spore-bearing zones. Ligule pits are present on the adaxial surface of vegetative leaves. The stems are essentially herbaceous but robust and 4-6 cm in diameter. Small amounts of periderm and wood were produced but primary tissues were not disrupted. Polysporia is the 1st herbaceous lycopod with an alternation of fertile and vegetative areas found in Pennsylvanina peats and is compared with Spencerites, Sporangiostrobus and Lepidodendron dacrydioides (proposed vegetative stem of Sporangiostrobus) which are suspected to have similar structure. The rarity of Polysporia in coal balls and its frequent associations with Sphenophyllum, combined with low numbers of arborescent lycopods, Psaronius or Medullosa, suggest an environment of growth not frequently encountered in coal-ball studies of the swamps. Polysporia may have grown in marginal wetland environments where herbaceous and low shrubby plants predominated; this suggests that some Endosporites-rich coals of the Upper Pennsylvanian are derived in large part from marshland peats.

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