Reinvestigation of Cardiocarpus minor (Wang) Li nomen nudum from the Lower Permian of China and its implications for seed plant taxonomy, systematics and phylogeny

A single species of cardiocarpalean ovule from the Lower Permian Taiyuan Formation of northern China is reinvestigated in order to characterize unknown features of its anatomy and to determine its identity. This species is distinguished by its highly vascularized nucellus and integumentary organization, conforming to the features of Cardiocarpus and Nucellangium , previously being assigned to both genera. To resolve this uncertainty a cladistic analysis of 25 ovule species from 12 ovule genera, including the new species, has been conducted. Results demonstrate non‐monophyly of Cardiocarpus and support monophyly of Callospermarion (with two species), Diplotesta (with two species) and Mitrospermum (with four species); the latter excluding M. bulbosum that is demonstrated to be a hydrasperman seed‐fern. Strict consensus results place Nucellangium at the base of a clade including Rhabdospermum and Diplotesta that occurs terminally on the tree and within a weakly resolved clade that includes two species of Cardiocarpus as well as Taxospermum . The ovules described here occur among several species of Cardiocarpus , Cycadinocarpus and Plectiliospermum that are situated below the terminal clade and above a clade comprising Mitrospermum / Callospermarion . This position is separated from Nucellangium inferring them not to be a second species of that genus, with these results supporting the generic level distinction of Nucellangium . As the ovule species described here fits within the generic circumscription of Cardiocarpus and occurs within the phylogenetic range of this genus, we have assigned it to Cardiocarpus and in doing so erect the species C. taiyuanensis nom. nov., noting the name C. minor is occupied by specimens belonging to another species. Other implications of the results are discussed, including potential systematic and taxonomic revisions, as well as the potential of identifying affinities for cardiocarpalean ovules for which parent plants are unknown. However, we refrain from conducting formal taxonomic procedures in order to segregate the unnatural genus Cardiocarpus , as we considered these results to be a first approximation at cardiocarpalean systematics and taxonomy. This investigation also emphasizes the need for critical reinvestigation of a several previously described ovule species for which existing evidence is tantalizing but insufficient to warrant inclusion into more comprehensive treatments of seed plant taxonomy, systematics and phylogeny. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 151–175.