Status and Relationships of the Chinese Endemic Platycraspedum (Brassicaceae)

Abstract

The generic limits and relationships of Platycraspedum are discussed, and the new species P wuchengyii is described. It is most closely related to Taphrospermum, from which it differs by having toothed filaments of median stamens, 2-lobed stigmas, palmately veined leaves, unequal sepals, and minutely reticulate seeds. As delimited here, Platycraspedum O. E. Schulz consists of two Chinese species endemic to eastern Xizang (Tibet) and neighboring Sichuan. Schulz (1922) compared the generic type, P tibeticum, with Dilophia Thomson and later (Schulz, 1936) placed both genera in the tribe Lepidieae. However, Platycraspedum does not have angustiseptate fruits, a feature Schulz (1936) used primarily to define the limits of Lepidieae. In our opinion, Platycraspedum, along with Dilophia, Taphrospermum C. A. Meyer, Lignariella Baehni, and several other genera, should be closely associated with Cardamine L., all of which share flattened replums, a feature very rare elsewhere in the Brassicaceae. The present paper does not aim to present the tribal alignments of these genera; nonetheless Schulz's (1936) placement of Platycraspedum in the Lepidieae is unwarranted. Platycraspedum is most closely related to Taphrospermum, a genus of seven species (Al-Shehbaz, unpublished) distributed primarily in' China. Both genera have fleshy fusiform roots, a whorl of scalelike leaves at the root base, petiolate cauline leaves, bracteate inflorescences, white petals, basally dilated median filaments, and flattened replums. Platycraspedum is readily separated from Taphrospermum by its palmately veined cauline leaves and bracts, minutely reticulate seeds, strongly flattened and toothed median staminal filaments, unequal sepals with the lateral pair saccate, poorly developed lateral nectaries with the median ones lacking, and 2-lobed stigmas. By contrast, Taphrospermum has pinnately veined cauline leaves and bracts, foveolate or rarely papillate seeds, terete and toothless filaments, equal and nonsaccate sepals, well-developed annular lateral nectaries confluent with median ones, and entire stigmas. Platycraspedum can easily be confused with some species of Eutrema R. Brown sect. Wasabia (Matsumura) 0. E. Schulz, but it can be separated by its strongly flattened and 1-toothed median filaments, flattened replums, non-mucronate leaf teeth, subsessile fruits, unequal sepals with the inner pair saccate, 2-lobed stigmas, and lack of septa. Eutrema has slender and toothless median filaments, terete replums, mucronate teeth or leaf-vein endings, stipitate fruits, equal sepals with the inner NOVON 10: 1-3. 2000. This content downloaded from 157.55.39.78 on Sun, 19 Jun 2016 06:11:43 UTC All use subject to http://about.jstor.org/terms