Pothos L. is a genus of c. 70 species of subtropical and tropical, predominantly forest root-climbing lianes distributed from Madagascar to Western Oceania (east to Vanuatu) and China (north to Hubei) to Australia (Queensland, New South Wales). The greatest diversity is met with in Indomalesia where the largest concentration of species and widest diversity is to be found in Borneo (see e.g., Hay et al. 1995).
Pothos is placed in tribe Potheae (sensu Mayo et al.1997), a palaeotropical assemblage of three very similar, possibly inseparable, genera. Besides Pothos, the other genera, both monospecific, are Pothoidium Schott and Pedicellarum M. Hotta. For discussion of generic delimitation in Potheae see Boyce & Hay (1998).
Linnaeus (1753, 1763) treated Pothos as a genus of climbing aroids with bisexual flowers. Subsequently many climbing aroids were included to form a heterogeneous assemblage. Early in the 19th century Schott recognized that Pothos was, as then defined, ‘unnatural’ and in a series of papers (Schott 1832, 1856 – 1857, 1860) redefined bisexual-flowered aroid genera. The current circumscription of Pothos is essentially that of Schott (1832, 1856 – 1857, 1860). Schott (1856 – 1857) established two subgenera, Pothos (as EuPothos) and AlloPothos. Engler (1905) further subdivided Schott’s subgenera (referring to them as sections) into seven series. While accepting Schott’s subgenera, no attempt is made here to follow Engler’s series.
Since the last revision of Pothos (Engler 1905) several geographical reviews have been published (e.g., Li 1979; Sivadasan 1982; Nicolson 1988; Hay 1995). To date no critical account of the genus has been prepared for Peninsular Malaysia (but see Hooker 1893, Ridley 1925), Borneo (but see Miquel 1856; Ridley 1905 and Merrill 1921), the Philippines (but see Merrill 1923) nor Thailand and Indochina (but see Gagnepain 1942, Hu 1968 and Boyce & Nguyen 1995).
This review is based primarily on existing Thai, Chinese and Vietnamese collections and extensive fieldwork in Thailand, Vietnam and, to a lesser degree, China. The political situation in other parts of the region have necessarily limited greater study. By way of example the total number of Pothos collections located for Cambodia is four (representing two or three species), for Lao P.D.R., 14 (four species) and for Myanmar, 35 (two species) from a total of 645 collections seen.
As with previous papers (Hay 1995, Boyce & Hay 1998) no attempt to group species other than at the level of subgenus (and that primarily for convenience, to aid identification) has been made. It is still far from clear whether Pothos as currently defined is a monophyletic genus (see Boyce & Hay 1998 for discussion) and attempts to group species formally are premature pending current studies.