Malvastrum hispidum, the false mallow, is an annual warm-season herb endemic to portions of the southeastern and central United States and it has been listed as threatened, endangered, or presumed extinct throughout most of its historic range. While it is generally included within Malvastrum, its ancestry, origins, and true relationships are obscure. No morphologically similar taxa exist in North America. Its preferred habitat is in thin soils in depressions over dolomitic limestone but the populations are discontinuous or disjunct. Population sizes vary drastically each year depending on local conditions of rainfall and disturbance and its survival depends upon a persistent seedbank. The northernmost-known populations are in Illinois where the species is listed as endangered. Searches in 2000 found no individuals at isolated historic sites in LaSalle, Rock Island, and St. Clair counties but some large colonies in dolomite prairie remnants in Will and Grundy counties had thousands of individuals. Searches in 2001 resulted in the location of an additional single population in St. Clair County where it had been last seen in 1950. This may support the hypothesis for a Mississippi River valley migration route for the species. There are also nomenclatural problems for this species. Original type material has never been found, and a previous expert chose its original description as its lectotype. However, a single very early specimen of Sida hispida Pursh (the basionym) has been found, and it is not a Malvastrum. Potential implications of this find will be presented.

Key words: Illinois, Malvaceae, Malvastrum, nomenclature, rare plants