P. sect. Philopsammos G.S. Bunting,
Phytologia 60(5): 306. 1986.
TYPE: P. callosum K. Krause, var. ptarianum Steyerm.
Philodendron sect. Philopsammos is restricted to South America, known largely from the region of the Guiana highlands with extensions into the Amazon basin, occurring principally on white sand savannas, sandstone outcrops and on tepuis, rarely in alluvium in lowland forests. It is characterized by having usually terrestrial or epipetric, thick, creeping stems with mostly short internodes, mostly long persistent, mostly intact cataphylls, moderately long petioles, mostly erect, geniculate petioles, more or less oblong, elliptic to narrowly ovate, coriaceous blades, usually lacking any prominent posterior lobes and with usually distinct, sometimes moderately obscure primary lateral veins. Inflorescences are moderately large with pistils bilocular, rarely 3-locular and ovaries moderately numerous with axile placentation.
Included in the section are the following species:
P. canaimae G.S. Bunting, P. craspedodromum R.E. Schult., P. dunstervilleorum G.S. Bunting, P. dyscarpium R.E. Schult. var. dyscarpium, P. dyscarpium var. ventuarianum G.S. Bunting, P. peraiense G.S. Bunting, P. phlebodes G.S. Bunting, P. pimichinense G.S. Bunting, P. ptarianum Steyerm., and P. pulchrum G.M. Barroso, P. remifolium R.E. Schult., P. sabulosum G.S. Bunting, P. steyermarkii G.S. Bunting, and P. tatei K. Krause. Perhaps to be included in this group also is P. englerianum Steyerm. No species in the group occur in Central America.
In describing this section Bunting (1986) made no mention of how the section is distinguished from P. sect. Baursia (or any other section). This is a critical point since both sections have species with elongated blades and at least sometimes have primary lateral veins that are not markedly more prominent than the interprimary veins (secondary lateral veins). The section is presumably distinguished from P. sect. Baursia on the basis of having mostly two locules per ovary. As an indication of its affiliation with P. sect. Baursia, Bunting specifically mentioned P. callosum, (a species included by Krause in P. sect. Baursia) as being a possible member of P. sect. Philopsammos. Philodendron ptarianum, has proven to be closely related to P. callosum, but that species was described by Krause as being "plurilocula", i.e., with many locules per ovary and "pauciovulata", i.e., with few ovules per locule. If this is true, the single character separating P. sect. Philopsammos from P. sect. Baursia, namely the small number of locules per ovary, would break down even in two subspecies (as now recognized by Bunting in his treatment of the Araceae in the Flora of the Guayana Highlands (Bunting, in press), one of which is the type of P. sect. Philopsammos. Bunting suggested that P. ptarianum might be synonymous with P. callosum. Investigations of one collection of P. callosum, Davidse & Miller 27269, had 2-locular ovaries with 8-10 ovules per locule with unusual black, shiny seeds. It would appear to clearly be a member of P. sect. Philopsammos. Thus it appears that P. callosum, up to now a member of P. sect. Baursia is a member of P. sect. Philopsammos.