See Korotkova Thesis 2011
Pfeiffera monacantha (Griseb.) P.V.Heath in Calyx 4(4): 158. 1994.
= Rhipsalis monacantha Griseb. Abh. Konigl. Ges. Wiss. Gottingen 24: 140. 1879. Holotype: Argentina, Salta, San Andr6s (west of San Ramon de la Nueva) Oran, 25. Sep. 1873, Lorentz & Hieronymus 453 (GOET), isotype US 603291.

Key to the subspecies
1.Stem-segments angled or flattened, spines l-2 or more, pericarpel angled, often spiny
subsp. monacantha
- Stem-segments flattened, spines absent, pericarpel not spiny. subsp. kimnachii
(Doweld) Ralf Bauer in Cactaceae Syst. Init. 19: 8. 2005.

= Acanthorhipsalis monacantha subsp. kimnachii Doweld in Sukkulenty 4(1-2): 41. 2001- publ. 2002.
Replaced synonym:
Rhipsalis monacantha var. espinosa Kimnach in Cact. Succ. J. (Los Angeles) 67(1): 38. 1995. Holotype: Bolivia, dept. Cochabamba, road from Cochabamba-Chapare highway to Tablas, 1974, Aguilar s.n. in Kimnach 2757, cult. Huntington Bot. Gard. 51587 (HNT), isotypes: HEID, US.

Pfeiffera monacantha (Grisebach)Heath Calyx, 4(4); 158. 1994 see Hunt in Cact. Syst. Init. 14: 2002
Lepismium monacanthum (Grisebach) Barthlott in Bradleya 5 (1987)
Desc from B&R 1923 & CSJ(US) p38 (1995)
Body - mostly pendant;
Stems - 2 - 3cm broad, to 45 cm long, flat or 3-angled, serrate;
Areole - to 1.2cm apart;
Spines - 1-6, to 1 cm long., also a few bristles;
Flowers - to 1.5 cm long, waxy orange, with small scales and felt; (Note that Britton and Rose show these incorrectly as white)
Fruit - spherical, to 1 cm ?, orange at first, then orange-red or paler, scaly;
Seeds - . dark brown.

DISTRIBUTION Bolivia (Cochabamba, Santa Cruz, Tarija), Argentina (Jujuy, Salta): at 300 - 2000 m altitude.

From Bradleya 13
Kimnach’s recently published description of a new variety espinosa [Cact. Succ. J (US) 67: 37 - 39 (1995)] has highlighted the diversity within this species, but the decision as to whether sub-species should be recognised must await further studies in the field.