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Studies of the Icacinaceae---III. A revision of Emmotum

1942; Arnold Arboretum of Harvard University; Volume: 23; Issue: 4 Linguagem: Inglês

10.5962/bhl.part.18686

2474-3283

Richard A. Howard,

Plant Diversity and Evolution

With Jour platesThe genus Emmotum is the largest genus of the New World Icacinaceae.It now includes twelve species and is limited to northern South America, being centered in the Amazon basin.Few of the species are widespread and several are.knownonly from a single mountain.The genus is easily recognized and is quite distinct among the Icacinaceae.Van Tieghem was so impressed by its characters that he established it as the sole genus of a separate family, the Emmotaceae, allied to the Icacinaceae.The characters upon which he recommended this separation are pronounced; however, such family characters of the Icacinaceae as articulated flowers, valvate aestivation of the corolla, alternate stamens, and two pendent anatropous ovules, of which but one matures, are shared with his segregated unit and it seems preferable to retain it within the Icacinaceae.Hamilton described Emmotum in 1825, crediting it to Desvaux.Miers was the first to recognize that Pogopetalum, which Bentham described in 1841, was identical with Emmotum.Engler, in 1872, proposed a division of the genus into two sections, which he called Longistyia and Brevistyla, These groups were based on differences in the petals, stamens, and pistils.Sleumer has accepted this same division, but he established subgenera and substituted the names Eucmmotum and Pogopetalum for Engler^s sections.The second section originally contained £. nitens (the type selected by Sleumer) and E. glabrum.Unfortunately, the latter species does not have the characters of the section and cannot belong there.This error may be traced to an inaccurate plate of Miers.These illustrations are confused and apparently there was an interchange of parts of the two species represented.Isotypes of the species and examination of the original descriptions show this clearly.By removing E, glabrum from the subgenus Pogopetalum (i.e. the section Brcvistyla Engler), only E. nitens remains.Since the usefulness of this monotypic subgenus is doubtful, it seems advisable to abandon it.The genus Emmotum is, accordingly, undivided in this paper.When van Tieghem proposed the Emmotaceae as a segregated family, he also separated £. nitens as a distinct genus, Pogopetalum.The characters justifying this newly proposed genus were those previously used by Engler as characters of his section Brevistyla, I am treating Pogopetalum van Tieghem as a synonym of Emmotum.