Zonal thermogenetic dynamics of two species of Philodendron from two different subgenera (Araceae)

Spadix temperature was measured in two species of Philodendron : P. melinonii (subgenus Philodendron ) and P. solimoesense (subgenus Meconostigma ). For each species, the temperature of the male zone, the sterile male zone and the female zone of the spadix were recorded. In both species, the temperature of the male zone warmed up at the beginning of each of the two flowering nights. In P. melinonii , the temperature of the male sterile zone increased the first day but remained not significantly different from that of the ambient air during the second day. The temperature of the male zone warmed up slightly on the second day. In P. melinonii , the temperature of the three zones was not significantly different from that of the ambient air between the two peaks. In P. solimoesense , the temperature of the male zone and sterile zone rose to above that of the ambient air during the first night and then progressively cooled down but remained 3–6°C above the ambient air temperature until the second peak. In both species the temperature of the female zones remained more or less constant during the entire flowering cycle, very close to the temperature of the ambient air. We suggest that the heat production and the spadix temperature patterns observed may reflect a general physiological process common to all species of Philodendron . The biphasic pattern present in the subgenus Meconostigma can be seen as a variant of the 'two peaks' pattern, occurring in the subgenus Philodendron , with a 'plateau' phase between them. The comparison of the different thermogenic cycles occurring in Philodendron , Arum and Dracunculus seems to indicate some clear evolutionary trends. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 79–86.