Ginkgoalean ovulate organs and seeds associated with Baiera furcata-type leaves from the Middle Jurassic of Qinghai Province, China

Abstract

Ginkgoalean ovulate organs Yimaia, detached seeds and the associated Baiera-type leaves are described from a paper coal at the uppermost part of the Middle Jurassic Shimengou Formation in the northern border of the Qaidam Basin, Qinghai Province, Northwest China. The organ bears a cluster of at least 3 orthotropous ovules at the apex of a peduncle. The seeds (ovules) are sessile, nearly rounded or broadly ovate to oblong, about 7 mm long and 5.7 mm wide, with an obtusely acute, acute or mucronate apex. Despite a general resemblance in gross morphology, the new Yimaia organ is distinguished from other species of the genus in the stomatal structure of the integument. Associated leaf segments of Baiera bear a resemblance to the Yorkshire Middle Jurassic species B. furcata, but are somewhat different in cuticular structure. Selected Mesozoic leaves with well-preserved cuticle and other Baiera type leaves that are known to have been associated with the Yimaia-type ovulate organs from China and other parts of the world are found to be different either in gross morphology and/or in cuticular structure from the present associated leaf segments. Yimaia ovulate organs and vegetative leaves dominantly of the Baiera-type appear to form a regular combination in the Mesozoic ginkgoaleans. They represented a rather small, but coherent plant group (Yimaiaceae) that was widely distributed in the Jurassic of Eurasia.