中国科学院南京地质古生物研究所机构知识库

Ovule-bearing structures of Karkenia are recorded from the Middle Jurassic of East Siberia for the first time. A new species, Karkenia irkutensis sp. nov., described fromthe lower part of the Prisayan Formation (Aalenian) of the Irkutsk Coal Basin, is a compact, ellipsoidal to spherical structure consisting of numerous ovules. The entire structure is borne on a thin stalk. The pedicels of individual ovules are also thin and most likely recurved. Four membranes are preserved in the ovules: outer and inner cuticles of the integument, the nucellar cuticle, and the megaspore membrane. Additionally, numerous large resin bodies occur in the sarcotesta. Among the ovules of the same ovule-bearing structure, two types of the megaspore membrane with different ultrastructure were obtained, which may indicate different stages of ovule development. Ovule-bearing structures of K. irkutensis were found in association with leaves of Sphenobaiera vigentis and their co-occurrence in the same samples from the Irkutsk Basin suggests that these remains were most likely produced by the same plant. Numerous dispersed seeds described as Allicospermum sp. were also found in the same locality. These seeds are similar to the attached ovules of K. irkutensis in form and size, but differ in having a thicker sarcotesta, smaller resin bodies. There are also differences in some features of the outer epidermis of the integument. Allicospermum sp. may represent more mature seeds/ovules of K. irkutensis. The morphology and epidermal features of the genus Karkenia are discussed. (C) 2021 Elsevier B.V. All rights reserved.