Phoxanthus manausensis W. A. Rodrigues, Inst. Nac. Pesqu. Amaz. Bot. Ser. 17: 3-7. 1964. “Brazil, Amazonas, Manaus, margem do igarapé do Buião ... W. A. Rodrigues & J. Chagas 4463, fl. 24-V-62 ... W. A. Rodrigues & J. Chagas 4680, 5-X-62, frutos . . No type examined.
My concept of O. manausense is derived almost entirely from study of two collections from upper tributaries of the Amazon in Peru: Amazonas: mouth of Río Santiago, Tessmann 3972 (NY). Loreto: Florida, Río Putumayo, at mouth of Río Zubineta, alt 280 m, Klug 2209 (K, US). These have almost the flower of O. heterophyllum, but the inflorescence arises from axils of compound leaves, and the leaflets are smaller, more chartaceous, and have fewer, less strongly impressed secondary veins. The aspect of these Peruvian plants is distinctive and I have no doubt that they represent a species other than O. heterophyllum. However, in absence of authentic Phoxanthus manausensis, I am less confident about my interpretation of the nomenclature. The protologue of P. manausensis, accompanied by figures and a photograph of part of the type-series, agrees in most details with the Peruvian species. The panicle of flowers on the single tree of P. manausensis seen by Rodrigues is larger than the average collected by Klug and Tessmann in Peru, but I cannot attribute great importance to this character. The panicle is described as more than 6 dm, with secondary branches up to 5 dm long, but the phototype shows that it can be about 4 dm long, less ample, that is, than now known for O. heterophyllum and only slightly larger than in the Peruvian specimens here referred to O. manausense. There may well be more significant differences in the leaf venation, the blades in Peru showing only 5-7 pairs of secondary nerves, in contrast to “about 8-12 pairs” described for P. manausensis. So much is certain that O. heterophyllum is distinct from both Brazilian and Peruvian elements here combined as O. manausense; whether the two latter are conspecific I do not have the material to judge.