Permineralized seed plants from the Upper Permian of southern China: a new species of Cardiocarpus

A new species of permineralized ovule is reported from a previously undocumented diverse fossil plant assemblage preserved in volcaniclastic tuff from the Late Permian Xuanwei Formation at the Huopu coal mine in Guizhou Province, China. The ovule is large and platyspermic, with 180 degrees rotational symmetry. It has a pronounced commissure that distally divides the integument into two valves. The integument comprises a twopart sarcotesta, a sclerotesta also divided into two parts, and an endotesta that is unusually thick in the central part of the ovule and at the apex. Fusion of the nucellus to the integument occurs only at the chalaza, and the nucellar apex is small, consisting of a proximal pollen chamber and a distally extending tubular projection. A single vascular bundle enters the base of the ovule and divides in the major plane at the boundary of the inner and outer sarcotesta to form two integumentary bundles, one to each side of the ovule, with the nucellar bundle continuing to the base of the nucellus, where it forms a small vascular cup. The gross morphology and the pattern of vascularization of the ovule fit the circumscription of the morphogenus Cardiocarpus Brongniart, to which the ovule is here assigned, but are distinct from previously recognized morphospecies leading to the erection of Cardiocarpus huopuensis sp. nov. In C. huopuensis sp. nov., tissues of the outer sarcotesta are rarely preserved and where present occur external to a zone of poorly preserved cells that suggests exfoliation of the outer sarcotesta through ontogeny. Although the identity and, hence, affinity of the parent plant for C. huopuensis sp. nov. are unknown, previous evidence shows ovules of this kind to be produced by either a coniferophyte or a seed fern (pteridosperm).