Synonymy
Epiphyllum nelsonii Britton & Rose (1913) Contr. U. S. Nat. Herb. 16:257
Phyllocactus nelsonii (Britton & Rose) Vaupel (1913) Monatsschr. Kakteenk. 23:116
Phyllocactus chiapaensis J. A. Purpur (1918) Monatsschr. Kakteenk. 28:118
Chiapasia nelsonii (Britton & Rose) Britton & Rose (1923) The Cactac. 4:203
Disocactus nelsonii (Britton & Rose) Lindinger (1942) Bot. Centralbl. Beih. 61:383

Ethymology
Nelsonii refers to E. W. Nelson, who disovered the plant in 1896. The former generic epithet was taken from the Mexican state in which it grows.

History
The plant was discovered in Chiapas, Mexio, in 1896 and Britton & Rose described the speices 17 years later out of a herbarium specimen. In 1913, C. A. Purpurs rediscovered the species and sent cuttings to his brother in, J. A. Purpur, in Germany. Five years later, unaware of the first publication, because of the war, J. A. Purpus described it again, this time as Phyllocactus chiapensis.

Origin and habitat
Mexico (Chiapas) and Guatemala. Epiphytic on evergreen oaks in the rainforest, exposed to cool, moisture-ladden north winds. 1.000-2.000 m alt.

Systematics
D. nelsonii is a distinct species and easily recognized, most closely related to D. biformis and D. eichlamii.

Cultivation
In semishade; the compost should contain a good proportion of  peat and always kept slightly moist; however the plant is sensitive to any excess moisture. Best kept at min. 10ºC (50ºF) in winter.

Other varieties
Disocactus nelsonii v. hondurensis Kimnach from Honduras has purplish stamens, rather than creamy. The variety will be presented sepatately.

Hybrids
Disocactus 'Frühlingsanfang'
Disocactus ´Pinky'

Description (var. nelsonii)
Stems pendent to 200 cm, primary stems terete, to 140 cm long, 6-12 mm thick, apically flattened for 5-30 cm; areoles in 3 rows, internodes 4 cm, those near stems bases often with white bristles, to 5 mm long;. secondary stems flat, to 40cm long, (2-)3(-6) cm wide, 2-6 mm thick, oblanceolate, obtuse when growning, acute when mature, margins obtusely serrate; areoles with wool and 1-3 white britsles up to 2 mm long; epidermis green, reddish brown when growing.
Flowers usually from apical areoles, 9-11 cm long, 5-7 cm in wide, diurnal, nonfragrant; pericarpel ca 6 mm long and wide, green; entire receptacle 3-4 cm long, ca 5 mm wide at middle, ca 1 cm wide at apex, strongly curved on pendent branches, ascending of horizontal, green, brownish at apex, bracteoles adpressed, deltoid, widely ovate, less than 1 mm long and 2 mm wide, brownish; outer tepals linear-lanceolate, acute 4-6 cm long, 1-2 cm wide, grenish yellow with light pink margins outside, darker pink inside; inner tepals oblong-lanceolate, acute or obtuse, purplish pink; stamens many, inserted in 2 zones, declining, excertad beyond the tepals, whitish cream; style 9-10 cm long, exceeding the stamens; stigma lobes 4-7, papillose, about 8 mm long.
Fruit subglobose, ca 15 mm long, nearly as thick, brownish red. Seeds 1,5 - 1,75 x 0,5-0,75 mm thick, brownish black.