Candole, A.L.P. de, Candolle, A.C.P. de, Monographiæ phanerogamarum prodromi, vol. 5: t. 18 (1883-1887) [W.H. Fitch] This may be the earliest illustration of the species. A few years later, what appears to be a photograph of a herbarium specimen was published in Illustrationes Plantarum Europæ rariorum.