A Preliminary Taxonomic Revision of Heteropsis (Araceae)

Heteropsis Kunth (1841) is one of the most poorly known genera of the Araceae (Croat 1998). Although widely distributed in the neotropics and of regional economic importance as the source of a valued root fibre, there has been no attempt at a taxonomic revision since Engler’s (1905) treatment for Das Pflanzenreich.
The reasons for this state of affairs are not hard to find. At first sight, most species do not even look like aroids because of their unusually short petioles which lack the well-developed sheath typical of most Araceae. Their hemiepiphytic life form makes it difficult to understand the plants as a whole, even morphologically. Many climb high into the canopy of primary forests where their flowering and fruiting take place and, as a result, the colors and forms of their living reproductive organs have often only recently been recorded during detailed forest surveys (Ribeiro et al. 1999). The complexity of the extended body of the plants, from seedling to mature flowering branches, is still only understood in the few species that have been most intensively studied (Soares Morais 2008). Most species remain known to the taxonomist principally through the study of herbarium specimens, which are usually incomplete. The typical herbarium specimen consists of a fertile branch with a post-floral/pre-fruiting inflorescence, but many others are sterile and taken from attached shoots, the leaves of which are normally distinct from those of fertile branches, at least in size if not also in shape and texture. Even the mature leaves of many species are not easy to distinguish. Many published descriptions are incomplete, especially in details of the inflorescence and infructescence; some species are still known only from the type material.
Above all, Heteropsis is a genus centred in Amazonia, where the Araceae are still only partially known, particularly the geographical distribution of already recognized species. It is to be expected that range extensions and the discovery of new species will result from future field studies there. However, the recent growth of interest in Heteropsis as a plant of economic importance in Amazonia has highlighted the need for a new taxonomic treatment, to summarize existing knowledge, revise species delimitations, and provide an identification key. Cipo´ -titica, as Heteropsis is known in Brazil, is part of the extractivist economy of Amazonia as a source of a highly resistant fiber used inmaking craft products and is a native plant of significant economic importance in the region. A number of ecological and ethnobotanical studies, mostly of recent decades, have focussed on Heteropsis roots (Galva˜o 1959; Milliken et al. 1992; Potiguara and Nascimento 1994; Hoffman 1997; Fadiman 2003; Knab-Vispo et al. 2003; Plowden et al. 2003; Durigan and Castilho 2004; Rondon 2005). Species delimitation and identification are an important support for the development of sustainable management practices of the wild populations which continue to be the sole source of the root fiber.
The revision presented here brings the taxonomy of the genus up to date in so far as existing collections permit, but is underpinned by recent detailed work in the Reserva Florestal Adolpho Ducke near Manaus (Ribeiro et al. 1999; Soares and Mayo 1999; Soares Morais 2008; Soares et al. 2009, 2011). Based on populations of seven species in one area, these studies have brought to light many new or previously poorly known morphological details, including life cycle, shoot architecture, leaf morphology, root anatomy, ecology, and reproductive morphology. This work demonstrates the need for intensive field studies, even to describe adequately the morphology.
For the reasons outlined above, the present revision should be considered preliminary to a more definitive future treatment. Nevertheless, it will provide a useful basis for ecological and conservation work and we hope it will also stimulate further taxonomic studies of the genus.