Revision of Dendraena pinnatilobata Nemejc from the Pennsylvanian of the Czech Republic

Dendraena pinnatilobata Nemejc is a Pennsylvanian true fern, which is known from the Stradonice locality (Czech Republic) only. All specimens of Dendraena pinnatilobata are preserved as three-dimensionally in volcaniclastic of Whestone Florizon (Radnice Member, Kladno Formation). Revision of this species includes detail study of pinnae and pinnules morphology, sporangia, in situ spores and a rachial anatomy. Combination of several methods was used including camera lucida, maceration of sporangial/spores, SliM observation and cross sections of rachides for precise description of this species. D. pinnatilobata pinnae were borne on the rachides of the Anachoropteris robusta-type anatomy. This real organic connection between pinnae/pinnules (including reproductive organs) and rachial anatomy is rare in fossil record. This knowledge is very important for understanding of a leptosporangiate fern evolution. Sporangia of Dendraena, pinnatilobata are annulate with band-lateral-upper type of annulus and in situ spores of the Microreticulatisporites harrisonii type, described for the first time, are unique for D. pinnatilobata. Based on this type of sporangia the species belongs to the leptosporangiate ferns. According to the petrological and sedimentological study of host sediments it is possible to infer that specimens of Dendraena were transported a short distance. Transport was very fast and fossils were deposited in supercritical conditions, which resulted in rapid burial of the plants and their excellent preservation. The plant host rock Whetstone Horizon also contains abundant volcaniclastic components. D. pinnatilobata grew in close proximity to the riverside or the peatland margins.