Synonymy
Cereus biformis Lindley (1843) Edward's Bot. Re. 29. Misc. 51
Disocactus biformis (Lindley) Lindley (1845) Edward's Bot. Re. 31: pl. 9
Disisocactus biformis (Lindley) Kunze (1845) Bot. Zeit. 3:533
Phyllocactus biformis (Lindley) Labouret (1853) Monogr. Cact. 418
Epiphyllum biforme (Lindley) G. Don in Loudon (1855) Encycl. Pl. ed. 3. 1378
Ethymology
Biformis (Lat.) = two-shaped. Refers to the stems. The primary are terete and the secondary are flat.

History
D. biformis was introduced into England in 1839. It had been collected by George Ule Skinner and sent to Sir Charles Lemon and later, Mr. Booth of Carclew, sent information about this new cacti to Lindley at Kew. It has been lost in cultivation for wquite some time, but now cultivated in Europe and probably also in the US.

Origin and habitat
Guatemala & Honduras. In mixed forests about 1.300 m alt.

Systematics
This species is close to D. eichlamii. Se table.

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. Being a highland plants it will not tolerate hot, dry conditions. Best kept at min. 10ºC (50ºF) in winter.

biformis

eichlamii

stem width

10-20 mm

(15-)30(-50)mm

outer tepals

spreading

not spreading

stamens

slightly exserted

much exserted

Description
Stems pendent to 200 cm or longer, primary stems terete, obscurely winged or not, 4-6 mm thick, woody at base; secondary stems flattened, narrowly elliptic, 5-15cm long, 10-20 mm wide, margins crenate or sinuate-dentate; areoles glabrous or nearly so; epidermis light or deep green.
Flowers usually produced from stems 2 years old, 5 cm long, 1 cm wide, diurnal, not fragrant; pericarpel ovate-oblong, green or brownish green, somewhat tubercled, with a few areoles subtended by small ovate bracteoles; receptacle ca 1 cm long, curved; outer tepals 4-5, spreading, curved at apex, linear, acute, magenta; inner tepals broader and more erect, linear-lanceolate, acute, magenta; stamens 10-12, slightly exserted, inserted in two series at the apex of the receptacle; style slender, purple; stigma lobes 4-5, 4 mm long, white.
Fruit ovoid, 1,5 cm, long, turgid, wine-colored.