Phoxanthus heterophylla Benth., Trans. Linn. Soc. 22: 126, tab. 23, 24. 1857. “In sylvis ad Rio Uapes juxta fines Brasiliae borealis (R. Spruce).” Holotype, Spruce 2487 (K, herb. Benth., 2 sheets) !
Of O. heterophyllum I have seen in addition to the type-collection five gatherings: one from Rio Uaupés near Taraquá (Pires 976, NY) and four from the neighborhood of Iquitos in Loreto, Peru (Tessmann 5143, NY; Klug 37, F, NY, US; Klug 1521, F, US; Ll. Williams 3719, F). The Peruvian collections do not actually show the leaf dimorphism supposed to characterize O. heterophyllum, but the large compound leaves closely match those of Spruce’s plant in size, texture, and venation.
According to notes made by Spruce in the field, already published in the protologue by Bentham, O. heterophyllum when standing alone takes the form of a small crooked tree, but in high forest becomes sarmentose, the flexuous upper branches threading through the canopy but not twining. The petals are described as pinkish when fresh, but as in other species of the genus turn brown when dried. It is difficult to make out from specimens the full size of the panicle, but at least one collected by Klug has a main axis 6 dm long with some lateral branches up to 4 dm long, a point that has a bearing on the distinctness of the following.