Jonas Lüthy’s thorough review of the Madagascan pachypodiums (Bradleya 22:85-129, 2004) seems, at last, to impose some much needed order to the P. rosulatum complex (in more than one sense) by recognizing a number of allopatric (geographically isolated) subspecies distinguished by “exclusive combinations of characters”. His review anticipates (p. 126) this new subspecies which was published shortly thereafter in the C&S Journal (77(1):38-42,46, 2005). Both this new subspecies and the increased understanding of this complex have been made possible through the ongoing fieldwork of Swiss explorers W. Röösli & R. Hoffmann. While investigating the southern limits of subsp. rosulatum’s range, they found this new taxon somewhat unexpectedly while detoured by impassible high water of the Manambaho river. Subspecies bemarahanse is distinguished by its erect, multi-branched habit, smaller pure yellow flowers that typically result in more fruits (up to five per peduncle), and in appearing to be confined to limestone substrate, namely the tsingy of Bemaraha, after which the subspecies is named. HBG 95212, plants from R&H 304, seeds collected Nov. 20, 2003, near Antsalova in the tsingy of Bemaraha, NW Madagascar, on eroded limestone rocks in xerophytic forest with P. menabeum. $30.
Published in the Cactus and Succulent Journal, Vol. 79 (2), March - April, 2007