Tenuisa frasniana gen. et sp. nov., a Plant of Euphyllophyte Affinity from the Late Devonian of China
Tenuisa frasniana gen. et sp. nov. is reported from the Late Devonian (Frasnian) Hunan Province of South China. Its axes are naked and narrow. Fertile stem is pseudomonopodial in branching and bears distichous lateral units. Fertile lateral units are subopposite and pseudomonopodial in the proximal part of stem, while they are alternate and isotomous two to four times in the distal part. They have tiny terminal sporangia that are paired and fusiform and that possess pedicels. Sterile ultimate units are dichotomous and terminate in tips recurving oppositely. Tenuisa resembles Psilophyton in pseudomonopodial fertile stem with alternate and dichotomous lateral units terminated by paired and vertically elongate sporangia. However, fertile lateral units are subopposite and pseudomonopodial on the basal part of stem, sporangial pedicels are present, and neither sporangial pairs nor sporangia themselves are twisted. This new plant differs from iridopteridalean cladoxylopsids mainly in the absence of whorled laterals and axial spines, and it differs from pseudosporochnalean cladoxylopsids in the absence of digitate lateral branches and the presence of sterile ultimate units with recurved tips. Because of these morphological differences and a lack of anatomical information, Tenuisa frasniana is currently left as incertae sedis within Euphyllophytina (sensu Kenrick and Crane).