Description from Flora of China
Herbs, evergreen, aromatic. Stem creeping, erect or ascending. Leaves long petiolate; petiole sheathing up to halfway, usually longer than leaf blade, frequently distinctly articulate ca. halfway along; leaf blade oblong, elliptic, lanceolate, deltoid, or sagittate, thinly to rather stiffly leathery, base usually cordate, apex acuminate usually with tubular tip; primary veins all diverging from midrib, with rather few basal, secondary veins striate, tertiary veins often numerous and very much thinner, all veins straight over most of their length, only near apex arcing into a submarginal vein. Inflorescences usually several together. Spathe persistent, often constricted. Spadix elongate; stipe very short or absent; female flowers usually each with an associated staminode; distal male zone usually separated from female zone by a ring of staminodes, very rarely a naked or near naked interstice; flowers unisexual, naked; female flowers: ovary incompletely 2-5-loculed with parietal and axile (very rarely basal) placentation, ovules numerous, semianatropous with long, slender funicle, style minute, stigma sessile or terminating a minute style, disciform or lobed; sterile flowers sometimes present at base of male axis of spadix; male flowers (fertile) consisting of 2-6 stamens, thecae extrorsely dehiscent by a slit, connective broad or narrow. Berry few or many seeded. Seeds on a long funicle, longitudinally striate, ovoid-lageniform.
Since the now long out-of-date full revision of Engler and Krause (in Engler, Pflanzenr. 55(IV. 23Da): 25-81. 1912), there have been fragmentary floristic accounts (Ridley, J. Straits Branch Roy. Asiat. Soc. 41: 169-188. 1905; Merrill, J. Straits Branch Roy. Asiat. Soc., Special Ed., 86-109. 1921; Alderwerelt van Rosenburgh, Bull. Jard. Bot. Buitenzorg 3: 163-229, 320-347. 1922; Furtado, Gard. Bull. Straits Settlem. 10: 183-238. 1939; Proc. 6th Paciﬁc Sci. Congr. (California, 1939) 4: 577-578. 1941), an uncritical species listing for Malesia focusing primarily on Sumatra (Hotta, Gard. Bull. Singapore 38: 43-54. 1985), a revision for New Guinea and the Bismark Archipelago (Hay, Blumea 44: 41-71. 1999), and various ad hoc new taxa (Hotta, Diversity Dynam. Pl. Life Sumatra, 73-120. 1986; Acta Phytotax. Geobot. 44(2): 93-96. 1993; Boyce, Kew Bull. 49: 793-801. 1994; Hay & Herscovitch, Gard. Bull. Singapore 54: 171-178. 2002), but no attempt has been made to undertake a full revision of Homalomena. The lack of a reliable taxonomy poses considerable problems for field workers given that Homalomena is one of the most speciose and taxonomically intractable aroid genera in the Asian tropics.
The problems presented by a lack of reliable taxonomy are compounded by the poor state of preservation of many of the historical types; the cryptic nature of most of the systematically significant morphologies, notably the presence, absence, and disposition of sterile flowers; the generally large and complex vegetative structures that do not lend themselves readily to traditional herbarium vouchering methodologies; and the fleeting anthetic period such that even well-prepared herbarium specimens are frequently taxonomically useless because inflorescences were prepared post-anthesis, by which time many significant structures had deliquesced or been subject to pre-preservation damage by the most frequent inflorescence visitors, chrysomelid beetles, and post-preservation destruction by herbarium beetles.
Homalomena is a taxonomically complex group and, notwithstanding the above difficulties, is in urgent need of a rigorous study aimed at resolving the taxonomy and phylogeny. This is imperative not only because Homalomena is one of the most abundant, speciose, and least well understood of the mesophytic aroid genera in tropical Asia, but also because the genus is now becoming the focus of interest for pharmaceutical research due to the terpenoids and flavonoids occurring in the plant tissues; such studies must have a basis in sound taxonomic understanding or they risk being futile.
About 110 species: tropical America and Asia; four species (two endemic) in China.
(Authors: Li Heng (李恒 Li Hen); Peter C. Boyce)