Synonymy
Cereus donkelaarii Salm-Dyck (1945) Allg. Gartenz. 13:335
Selenicereus donkelaarii (Salm-Dyck) Britton & Rose in L. H. Bailey   (1917) Standard Cuycl. Hort. 3141

Ethymology
Named after the van Donkelaar, the Netherlands, who sent cuttings to Salm-Dyck.

History
Even though one of the earlist described species still an anonymous one, not extremely rare in collections but not much i published about it. I have never seen a photograph of the flower.

Description
Stems scandent, clambering or sprawling, branching, producing aerial roots, stiff, 8 m long or more, 8-12 mm thick; ribs 6-10, often indistinct, rounded, almost terete in age; areoles 1,2 mm, with white wool, internodes (3-)8-17 mm, young areoles with white hairs; spines britstle-like, 10-20, or more, depressed, spreading and covering the stems, 3-7mm long, stiff, central spines 1-2, 2 mm long, stiffer than radials, brownish; epidermis dark green, sometimes brownish, smooth, margin of ribs purplish
Flowers ca 18 cm long, outer tepal limb 20 cm, inner tepal limb 10 cm, nocturnal, fragrant, outer tepals spreading, recuriving, inner tepals forming a cup; pericarpel spiny, but no hairs; receptacle 6-8 cm. long, purplish; outer tepals linear, reddish outside, white inside; inner tepals 6-9 cm long, ca 10-17 mm wide, entire, acuminate, white; stamens and style white, greenish at base, stigma lobes ca 20.

Reported to contain unspecified alkaloids.

Origin and habitat
Mexico: Yucutan, Quintana Roo and Belize. Sea level. Subcaducial tropical forstests. Plant usually terrestrial, more seldom epiphytic. The species form large colonies. It prefer shaded places protected by the canopy of trees.

Systematics
Easily recongized, but closely allied to the S. grandiflorus-complex.

Cultivation
An easily cultivated, fast growing species. Needs a compost containing plenty of humus and sufficient moisture in summer. Give a suitable fertilizer during the growing season. Should not be kept under 15ºC (59ºF) in winter. Best grown in semi-shade. Extra light in the early spring will stimulate budding. Flowers in early summer.