Frenguellia (Lycopsida) from the uppermost Devonian of West Junggar, Xinjiang Uygur Autonomous Region, NW China, and its implications on protolepidodendralean leaf morphology and paleophytogeography

Abstract

Protolepidodendralean lycopsids are characteristic of morphologically complex leaves. Most taxa of this group are herbaceous and widely distributed in global Devonian sediments, with exceptions of a few members, such as Frenguellia eximia from the Lower Carboniferous of Argentina. In this study, we focus on the morphology of Frenguellia eximia and emend its generic and specific diagnoses, based on new materials from the Upper Devonian Hongguleleng Formation of West Junggar, Xinjiang Uygur Autonomous Region, Northwest China, within the fossil-bearing bed palynologically dated as a latest Famennian age. This is the first finding of Frenguellia eximia out of Gondwana. Frenguellia eximia bears planate leaf with three upward pairs of lateral tips, isomorphic sporophyll to the leaf, and elongated, oval sporangium. Leaf morphology of the members of the Order Protolepidodendrales is summarized and classified into lateral-tip and distal-tip types. Lateral-tip type leaf consists of an obvious main body and several paired lateral tips, whereas distal-tip type leaf shows a petiole and a distal lamina with several planate or three-dimensional segments. Two leaf types probably indicate two independent evolutionary routes of microphylls evolving from simple leaf of pre-lycopsids during the Devonian period. The new occurrence of Frenguellia eximia further shows paleophytogeographical similarities between West Junggar and northwestern Gondwana.