Xerosicyos Humbert
Xerosicyos Humbert, Compt. Rend. Hebd. Séances Acad. Sci. 208: 220. 1939.
Type: Xerosicyos danguyi Humbert, J.-H. Humbert 2420 (P, holotype; TAN, isotype), Southern Madagascar.

Zygosicyos Humbert, Bull. Soc. Bot. France 91: 166. 1945.

Dioecious, perennial climbers or shrubs with herbaceous or woody shoots with rootstock or large, partially exposed pachypodium, to 1 m across. The leaves are shortly-petiolate, simple, trilobed or trifoliolate. The tendrils are apically bifid, glabrous or pubescent. The male flowers are produced in sessile or pedunculate fascicles, the female flowers stand solitary or in pedunculate fascicles. The receptacle-tube is reduced, flat with four small, lanceolate-deltoid sepals. The corolla is irregularly contorted, rotate or zygomorphic with four free, (long) lanceolate, yellow or yellowish-green petals. The four stamens are inserted near the mouth of the tube on free filaments or the filaments are fused in pairs in the lower half or united into a central column but free at the tip. The four anthers are all monothecous with reniform, horizontal thecae. The pollen is tricolporate, finely striate, small (polar axis 24-30 µm, equatorial axis 16-23 µm, (Keraudren 1968)). The ovary is obconical, bilocular at the apex and unilocular at the base. The two ovules per locule are more or less pendent. The two styles are straight and divergent with bilobed or horse-shoe-shaped stigmata. The fruit is an obconical, compressed, dry capsule, 2-3 cm long, apically dehiscent by the ventral carpellar suture, ripening yellow. The four seeds are elliptical, compressed, c. 1 cm long, with smooth, pale brown, narrowly winged testa.

The six species grow in dry forest and bushland in Madagascar.

Xerosicyos is placed in tribe Zanonieae, where it groups as sister to the clade comprising Zanonia and Siolmatra, from which it split about 49 million years ago (Schaefer et al. 2009, Schaefer & Renner 2011).

Literature

Eggli, U. 1998. First report of female flowers for Xerosicyos pubescens Keraudren (Cucurbitaceae). Cactus and Succulent Journal 70: 40-41.

Khunwasi, C. 1998. Palynology of the Cucurbitaceae. Doctoral Dissertation Naturwiss. Fak., University of Innsbruck.

Rauh W. 1996. Observations complementaires sur Xerosicyos pubescens (Cucurbitaceae) de Madagascar. Bull. Mus. Nation. Hist. Nat., B, Adans. 18: 161-166.

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.

Schaefer, H., Heibl, C., and S.S. Renner. 2009. Gourds afloat: a dated phylogeny reveals an Asian origin of the gourd family (Cucurbitaceae) and numerous oversea dispersal events. Proceedings of the Royal Society B 276: 843-851.