International Aroid Society

SIMILAR GENERA

Epipremnum is one of four Asian genera in Monstereae (sensu Mayo, Bogner & Boyce, 1997), the others are Scindapsus, Rhaphidophora and Amydrium. In Malesia these genera are mostly root-climbing lianes (see Schimper, 1903: 193), exceptions include, e.g. Scindapsus rupestris Ridl. (Peninsular Malaysia, Borneo; creeping rheophyte), Amydrium humile Schott (Peninsular Malaysia, Thailand, Sumatra; creeping to rarely climbing forest floor herb), Rhaphidophora beccarii Engl. (Peninsular Malaysia, Thailand, Sumatra, Borneo; creeping rheophyte)] occurring in a wide range of habitats [lowland dipterocarp forest (e.g. Rhaphidophora crassifolia Hook.f., Pasoh F.R., Negeri Sembilan, Malaysia) to montane kerangas (e.g. Scindapsus scortechinii Hook.f., Genting Highlands, Selangor, Malaysia)]. All genera except Amydrium have abundant trichosclereids in all tissues (sparse in Amydrium). These are observable by tearing a mature leaf lamina and looking for ‘hairs’ protruding from the damaged edges. All genera have spadices bearing bisexual naked flowers. Often the lower and uppermost flowers in a spadix are sterile and different in appearance. Lower sterile flowers are usually larger and free while those at the spadix tip are often smaller and partially fused to adjacent sterile flowers. In neotropical Monstera Adans. the basal sterile flowers usually produce a nectar droplet and appear to act as pollinator attractants (Madison, 1977). They perhaps function similarly in Asian genera. In most species observed to date the spathe gapes on opening and is swiftly shed at male anthesis (exceptions with partially persistent spathes include Scindapsus rupestris). In all but Amydrium medium (Zoll. & Moritzi) Nicolson and A. humile Schott the mature infructescence surface is comprised of tough thickened stylar tissue. When the infructescence is ripe the styles adhere to one-another and fall as irregular plates to expose the ovary cavity with the seed embedded in copious, variously coloured pulp.
Confusion can occur between Epipremnum and the other Malesian monsteroid genera. If fruits are mature, seed characters are useful in separating Epipremnum and Rhaphidophora. Epipremnum has fruits with few large, strongly curved, seeds with a bony, smooth to ornamented testa. The fruits of Rhaphidophora each contain many small ellipsoid seeds with a brittle, smooth testa. Alternatively, immature fruits can be dissected and the number of ovules counted (few in Epipremnum, almost always many in Rhaphidophora).
Certain Scindapsus [notably S. latifolius M. Hotta (Borneo), S. splendidus Alderw. and S. roseus Alderw. (both Sumatra)] are very similar in appearance to the entire-leaved Epipremnum species. The only way to differentiate these Scindapsus and Epipremnum species, aside from field experience, is to observe inflorescences or, better, semi-mature infructescences. Scindapsus has fruits with a solitary curved seed. However, certain Epipremnum species (e.g. E. ceramense and E. falcifolium) seem to habitually abort all but one ovule and produce fruits with a solitary seed. Older texts (e.g. Engler & Krause, 1908) state that Scindapsus seed is exalbuminous but recent studies of Araceae seed by Seubert (1993) have demonstrated that Scindapsus seeds do contain small quantities of endosperm. Nevertheless the embryo is still relatively larger in Scindapsus.
The sparse trichosclereids of all Amydrium species facilitates field identification of even sterile material to genus (see note above). Where confusion between individual species can occur [e.g. between Amydrium zippelianum (Schott) Nicolson, A. magnificum (Engl.) Nicolson and E. pinnatum] a note is included with the relevant species.
Species of Anadendrum Schott (tribe Anadendreae) are often collected as ‘Rhaphidophora’, ‘Scindapsus’ or ‘Epipremnum’. Anadendrum, together with most Pothos L. and Pedicellarum M. Hotta (both subfamily Pothoideae), are the only simple-leaved Asiatic aroid climbers with reticulate venation (Amydrium humile, also with reticulate venation, can occasionally be observed as a low climber, but then with a solitary inflorescence). Additionally, Anadendrum lacks trichosclereids and can be distinguished from all Monstereae using a leaf tear. Using floral characters Anadendrum (each flower with a membranous perigon of fused tepals) is a singular genus and should not be confused with any other asiatic climbing Araceae. Confusion can occur between Anadendrum and genera of Pothoideae (i.e. Pothos, Pothoidium Schott and Pedicellarum) that also lack trichosclereids. However, Pothos (except subgen. Pothos) and Pedicellarum are instantly recognizable by the intramarginal veins crossing the primary venation (for illustration see Hay, 1995). Anadendrum flowers on clinging climbing shoots whereas almost all Pothos flower on free lateral shoots. In fruit both have red, somewhat juicy berries. However, those of Anadendrum are apically truncate with a prominent linear stigma wheras Pothos has ellipsoid to globose berries with a tiny, punctiform to slightly elongated stigma. The critical characters for differentiating between the genera of Anadendreae and Monstereae in west and central Malesia are presented below as a dichotomous key.
Confusion is also possible at species level. Epipremnum pinnatum is vegetatively most similar to Rhaphidophora korthalsii Schott but easily-observed distinguishing characters are present. Mature leaves of R. korthalsii are invariably pinnatisect (variously pinnatifid, pinnatipartite or pinnatisect in E. pinnatum) with individual pinnae, even the narrowest, having more than one primary lateral vein (one per pinna in E. pinnatum). The internodes of R. korthalsii lack the prominent irregular longitudinal whitish crests and older stems lack the distinctive matt to sub-lustrous pale brown papery epidermis typical of E. pinnatum. The feeder roots of R. korthalsii are scaly whereas they are lenticellate-corky in E. pinnatum. The pre-adult stage of R. korthalsii is a ‘shingle’ climber with oblong-elliptic to ovate, slightly falcate, upwards pointing leaves overlapping in the manner of roof tiles. Juvenile plants of E. pinnatum are sprawling to climbing with long-petioled ‘conventional’ leaves. Fertile material of R. korthalsii and E. pinnatum is readily separated by the shape of the style apex [round to oval (R. korthalsii) versus angled (E. pinnatum)] and the shape of the stigma and its orientation to the spadix [punctiform and circumferential (R. korthalsii) versus linear and longitudinal (E. pinnatum)].
Epipremnum pinnatum and Rhaphidophora tetrasperma Hook.f., another pinnatifid and perforate-laminaed species can be confused. Juvenile R. tetrasperma is a shingle-plant similar in appearance to R. korthalsii. Flowering-size plants have smooth stems and unequal ovate-elliptic coriaceous laminae (longitudinally crested stems and more-or-less equal, ovate to oblong-elliptic and sub-membranaceous laminae in E. pinnatum) and a more scandent habit, with leaves scattered along sinuous stems. Rhaphidophora tetrasperma is a rather rare species restricted to a few sites in Peninsular Malaysia (Kelantan, Perak) and southern Peninsular Thailand (Narathiwat).

Some terms employed in the descriptions to follow may need clarification.
Monopodial stems Sterile stems, often of great length, that are monopodial. Such stems are usually only clinging and orthotropic (or nearly so).
Physiognomically monopodial stems Fertile stems, of variable length, with the appearance of being monopodial but that are actually sympodial with growth terminating by a, sometimes aborted, inflorescence. Such stems may be clinging and orthotropous (or nearly so) or free and plagiotropic to pendent.
Clasping roots Short specialized roots that anchor a climber, hemiepiphyte or epiphyte to its substrate, generally a tree or rock. Feeding roots Specialized roots arising from aerial stems which, extending down to the soil, transport nutrients to the plant. Shingle climber A type of juvenile morphology, found in climbers, in which the petiole is very short and the leaf blade relatively broad and more-or-less overlapping with its neighbours to resemble the tiles (or shingles) of a roof; such plants are found climbing up larger tree trunks; e.g. Rhaphidophora korthalsii
Compound primary lateral veins Vein type found in dried specimens in which a primary lateral vein is comprised of few to several vascular bundles (vs one vascular bundle in simple lateral veins). In fresh material such features are often obscured by the turgidity of the vein.
Interprimary veins A vein approximately parallel to and situated between the primary lateral veins.
Perigon The floral envelope of a flower in which there is no differentiation of calyx from corolla, it may be a single structure (connate tepals) or composed of individual, similar tepals.
Perigoniate Of a flower which possesses a perigone.
Circumferential orientation (of stigmas) Linear stigmas set parallel to the circumference of the
spadix axis.
Longitudinal orientation (of stigmas) Linear stigmas set parallel to the long axis of the spadix.

Trichosclereids Literally a hair-like sclereid; fibre cells (cells with thick, lignified walls) which are very slender and elongated so as to be visible to the naked eye as hair-like structures. On tearing the leaf blade they can be seen protruding from the torn edge.