Systematics and evolution of the genus Cakile (Cruciferae)

is probably the most extensive discussion of evolution within the tribe Brassiceae^ Rytz (1936) also argued that Cakile had evolved from Erucaria but, in addition, Cakile represents the basal stock for a group of genera constituting his subtribe Rapistrinae ( Calepina, Ceratocnemum, Cramhe, Didesmus, Kremeria, Muricaria, Rapistrum).Kyt/.'s views focused primarily on aspects of fruit morphology.In the Brassiceae he distinguishedbetween "valvar" and "stvlar" or "beak" portions of the mature fruit and postulated an evolutionary trend toward reduction of the valvar portion (reduction in size and in number of ovules and seeds), primary increase in the stylar portion or its elaboration into an appendage, and secondary reduction of the stylar portion of the fruit.He considered Cakile an intermediate in the reduction series from Erucaria leading to such presumably recent products of evolution as Cramhe.Calepina, and Kremeria.These trends in fruit morphology appear to be valid, but the neat linear series which Rvtz proposed for the evolution of the genera undoubtedly oversimplify a more reticulate pattern of relationships.Specifically, the series from Erucaria through Cakile to Rapistrum would involve a change in cotyledon position from conduplicate to accumbent back to conduplicate (Zohary 1966) and a change in ovular position along the replum from alternating on both sides to restricted to one side back to alternate ( Schulz 1936).It appears simplest to postulate a parallel series of reductions, with Cakile the end-point of one of these lines of evolution.An ultimate rather than intermediate status seems more consonant with the nearly unique strand habitat of Cakile (excepting C. arabica), otherwise rare in the Cruciferae.