A new euphyllophyte Kunia venusta gen. et sp. nov. from the Middle Devonian of Yunnan, South China

Abstract

Kunia venusta gen. et sp. nov. is reported from the late Middle Devonian (Givetian) Haikou Formation near Kunming City, Yunnan Province, China. This plant has three orders of naked axes that divide pseudomonopodially. The second-and third-order axes occur in a helix. Fertile appendages are distantly spaced and helically inserted to the third-order axis; they comprise equally dichotomous branches terminated by two clusters of paired and fusiform sporangia. Sterile appendages are dichotomous and distally recurved. A comparison is made with the basal euphyllophytes including the trimerophytes, cladoxylopsids, zygopterids, stauropterids, and some relevant genera of uncertain affinity. The new plant resembles them in dichotomous appendages with terminal elongated sporangia, but differs mainly in the three orders of pseudomonopodial axes bearing helical laterals. It is thus placed in the Euphyllophytina as incertae sedis. It is suggested that an evolutionary divergence in the branching pattern and appendage morphology might have occurred in the Middle Devonian euphyllophytes, that is, maintaining three dimensions versus yielding more or less planation. Key words basal euphyllophytes, Kunia venusta, Middle Devonian, South China.Euphyllophytina (sensu Kenrick & Crane, 1997) is a major clade of vascular plants that comprises ferns, sphenopsids, seed plants, and the stem groups leading to these three lineages. Basal euphyllophytes, such as the trimerophytes, cladoxylopsids, rhacophytaleans, and progymnosperms, are abundant in the Devonian of the world. As summarized, the Middle Devonian (Givetian) plants occur widely in the Xichong Formation of Zhanyi, Wuding, Luquan, and Huaning Counties of eastern Yunnan, South China; many of them are basal and endemic elements of the euphyllophytes, for example, Eocladoxylon, Panxia, Rhipidophyton, Tauritheca, and Tsaia. These plants lack typical pseudosporochnalean/iridopteridalean cladoxylopsids and aneurophytalean progymnosperms, which were common in the coeval floras of Laurussia and Gondwana continents . Middle Devonian plants in eastern Yunnan indicate a palaeogeographical isolation and local tropical palaeoclimate . In this paper, a new euphyllophyte plant of uncertain affinity is described from the Givetian Haikou Formation, Kunming City, eastern Yunnan, China. It further indicates the endemic character- istics of the Middle Devonian flora of South China. Based on the morphological comparison with several plant groups and taxa, we discuss the classification of this plant and the evolution of the Middle Devonian euphyllophytes.