Szea yunnanensis sp. nov., a new leptosporangiate fern from the Lopingian of Southwest China

A new species of adpressed leptosporangiate fern, Szea yunnanensis sp. nov., is described from the Xuanwei Formation (upper Permian) of Yunnan Province, Southwest China. Fronds of this new species are at least bipinnate, with suboppositely to alternately arranged cladophleboid pinnules. Fertile pinnules are triangular to falcate shaped and show slightly decurrent entire bases, acute apices, and proximally lobed margins. Sporangia are grouped into abaxial sori arranged in one row on each side of the midvein from the basal to the 1/2-2/3 portion of the pinnule. The number of sori per row varies from one to four. Sori are exindusiate, ovoid/ellipsoid, with a diameter of 1.3 mm on average, and each consists of approximately 25 sporangia. Sporangia with biseriate annuli are ovoid or ellipsoid, approximately 330 mu m long and 230 mu m wide, and each produces approximately 100 or more spores. Sporangial walls have one layer of polygonal/elongated cells. Trilete auriculate in situ spores of the Triquitrites-type have verrucate-rugulate-reticulate sculpture. The exine is 2-3 mu m thick and without identifiable layers. The family relationship of Szea may belong to the Gleicheniaceae or Sermayaceae, but the combination of sporangium and spore characteristics of Szea inclines us to place this genus among Incertae Sedis. The family relationships of Chansitheca, Henanotheca, and Oligocarpia which were originally affiliated with the Gleicheniaceae are also questionable.