Perennial, herbaceous climber, to 12 m long and stems to 1 cm in diameter with dioecious sex system. The leaves are simple, petiolate, with ovate-oblong, entire blade and a small, oblong probract at the base of the petiolus. The tendrils are simple. The receptacle-tube of the small flowers is shallow. Male flowers are produced in racemes or panicles, the female flowers solitary. The five sepals are triangular, minute. The five pale yellow petals are elliptic, entire, free. The three stamens are inserted towards the base of the tube on free, short filaments. Two anthers are bithecous and one monothecous, free but appressed into a central head. The thecae are triplicate with tricolporate, micro-reticulate-gemmate pollen in tetrads, these ca. 85 µm in diameter, the monads medium-sized (polar axis c. 44 µm, equatorial axis c. 59 µm, (van der Ham & van Heuven 2003)). The ovary is cylindrical-oblong with few, horizontal ovules. The style is cylindrical 9-10 mm long with three heart-shaped, papillose stigmata. The glabrous fruit is solitary, oblong, 8-10 cm long and 4-4.5 cm in diameter, indehiscent, ripening red. The few seeds are subglobose, c. 10 x 8-9 x 4 mm with smooth, faintly margined testa.
The only species, B. simplex, grows in tropical montane primary forest, 1000-1800 m a.s.l. in Borneo (Sarawak, Sabah).
Phylogenetically, Borneosicyos is sister to the Asian genus Solena and the two are close to Lemurosicyos from Madagascar.
Borneosicyos simplex W. J. de Wilde, Reinwardtia 11(3): 224. 1998.
De Wilde, W. J. J. O., Duyfjes, B. E. E. and R. W. J. M. van der Ham. 2003. Borneosicyos simplex (Cucurbitaceae) a veritable rare plant peculiar of Kinabalu Park. Flora Malesiana Bull. 14: 33-42.
Schaefer, H. and S.S. Renner. 2011. Phylogenetic relationships in the order Cucurbitales and a new classification of the gourd family (Cucurbitaceae). Taxon 60: 122-138.
Van der Ham, R. and B. J. van Heuven. 2003. A new pollen type in Old World Cucurbitaceae. Grana 42: 88-90.