See Korotkova Thesis 2011
Lymanbensonia micrantha (Vaupel) Kimnach in Cact. Succ. J. (Los Angeles) 56(3): 101. 1984. = Cereus micranthus Vaupel in Bot. Jahrb. Syst. 50: Beibl. 111: 19. 1913. Holotype: Peru, Puno, near Sandia, 31. July 1902, Weberbauer 1353 (B, destroyed), isotype: US.

Pfeiffera micrantha (Vaup) Heath , Calyx 4 (4): 158. 1994
Lepismium micranthum (Vaupel) Barthlott in Bradleya 5 (1987)
Desc from Kimnach in C&SJ (US) 55: 177-182. 1983
Stems - at first erect, later sprawling-pendent branching laterally or basally, to 100 cm long or more, (2-) 3-angled, 1.5 - 2 cm thick, crenate, the lobes protruding 2 - 4 mm, 1 - 1.5 cm wide, the margin subobtuse; leaflets at bottom of margin sinuses, inconspicuous, ap¬pressed, broadly truncate, ca. 2 mm wide and 1 mm long, yellowish green, later drying brown and usually hidden by a hemispherical mass of areolar wool, the latter profuse, sinuous or curly, less than 1.5 mm long, cream to yellow¬ish; spines ascending to expanding, straight, ca 6, 2 - 4 of these thicker and darker brown, the others thinner and yellowish, 5 - 10 mm long often with 1 - 3 others that are curving, thin¬ner, more hair-like and to 3 mm long;
Epidermis - yellowish green, dull, roughened because of slightly convex cells.
Flowers - arising near apices of older stems, tubular-campanulate, 27 mm long, the limb 24 mm wide, the opening at apex of flower ca. 4 mm wide;
Pericarpel - turbinate, ca. 4 mm long, ca. 6 mm thick at apex, brownish, faintly tinged yellowish, shiny, with ca. 9 podaria that are obtusely convex, 1 - 7 mm long and 1 - 5 mm wide,
Bracteoles - appressed, deltoid, 0.5 - 4 mm long and wide, acute, the upper ones slightly cuspidate, somewhat keeled on back toward apex, fleshy, usually subtending white wool less than 1 mm long; remainder of re¬ceptacle ca. 12 mm long, the exterior with 4 - 5 tiers of relatively large imbricating bracteoles 6 -18 mm long and 5 - 6 mm wide, the lower ones deltoid, acute, with apices appressed to erect, the upper ones oblanceolate, obtuse, mucronate, with the apical half strongly re¬curved, the apical portion of all bracteoles purplish red, the remainder pinkish white with a red margin;
Tepals - hardly distinguishable from the upper bracteoles except that they recurve only near their apices and the more apical ones are increasingly shorter and nar¬rower (to 10 mm long and 5 mm wide);
Ovule chamber - turbinate, ca 2 mm long and wide;
Nectaries - prominent, 3 - 4 mm long, yellowish;
Filaments - adnate to receptacle for another 7 - 8 mm, becoming free in a 1 mm-long zone at apex of receptacle, the free portion 5 - 7 mm long, all filaments straight, cream, ca. 0.3 mm thick; anthers oblong, ca 0.75 mm long and 0.5 mm wide, yellow;
Style - 2 cm. long, ca. 1 mm thick, magenta, lighter below, darker above; stigma lobes 5, rotate, 1.5 - 2.5 mm long and ca. 0.5 mm thick, heavily papillose, greenish-cream.
Fruit - globose to shortly cylindric, to 1 cm. long, slightly winged and with a few small bracteoles that subtend a rather prominent tuft of short brownish-yellow wool and sometimes a spine up to 2 mm long.
Seeds - numerous, somewhat narrowed at base, scarcely 2 mm long, black.

DISTRIBUTION Peru (Puno); epilithic at 2100 m altitude (known only from type locality).

Note from Bradleya 13
The morphology of this species has been described and illustrated by Kimnach (1983), taxonomic conclusions notwithstanding. The at first sight aberrant form and colour of the flower are obviously adaptations to hummingbird- pollination.

CACTUS & SUCCULENT JOURNAL (U.S.), 5: 177-182. 1983
Summary: The type species of Acanthorhipsalis Britt. & Rose (Cactaceae) is Cereus micranthus Vaupel, discovered in Peru by Weberbauer in 1902. Its distinctive flower, described and depicted in detail here for the first time, has a pronounced receptacle tube some 12 mm long and tepals that expand only apically. The other species that have been placed in Acanthorhipsalis have a floral tube less than 2 mm long and tepals that expand more widely. The genus was separated from Rhipsalis Gaertner primarily because of the presence of stem spines, an untenable character because it is found in varying degrees in several Rhipsalis species. Acanthorhipsalis is here upheld as a genus with A. micrantha as its only species. Two other species of Acanthorhipsalis are transferred to Rhipsalis as R. paranganiensis (Card.) Kimn. and R. brevispina (Ritt.) Kimn. Keys to the species of this alliance and to the three recognized genera of subtribe Rhipsalidanae Britt. & Rose (Acanthorhipsalis, Rhipsalis and Schlumbergera Lem.) are also provided.

In 1902 August Weberbauer, a well-known authority on Peruvian plants, discovered a small shrubby cactus growing among undergrowth on cliffs at an altitude of 2100 meters near
Sandia in southeastern Peru. Karl Schumann recognized it as a new species and labeled Weberbauer's herbarium specimen as "Rhipsalis peruviana", a name he never published.
Vaupel (1913) designated the same specimen as the type of his new species, Cereus micranthus. The type, deposited in the Berlin-Dahlem herbarium, was destroyed in a bombing raid during World War II. Stem fragments of Weberbauer's collection, sent by Vaupel to Rose in 1920, now comprise a dried specimen at the U.S. National Herbarium; this, as the only known surviving type material, was annotated by Kimnach and Hutchison in 1959 as the lectotype for the species. A photo of this specimen is fig. 211 in volume 4 of The Cactaceae (Britton and Rose, 1923).
Attached to the lectotype sheet is a note from Vaupel to Rose dated October 1920: "I enclose a slip and a flower of Cereus micranthus. I have described the plant as Cereus because I could not otherwise correctly classify it, and intended later to put it in its proper place on working up the entire group. It is of course not a Cereus in the stricter sense but belongs to the vicinity of Rhipsalis."
Later, Vaupel (1926) placed the species in Rhipsalis, but as R. asperula Vaup., because the original specific name had been pre-empted by R micrantha (H.B.K.) DC. His description mentions that the flower-tube is "scarcely longer than the pericarpel, broadly funnelform, with several small scales" and that the stamens "first become free at the upper margin of the tube." This clearly indicates the presence of a floral tube, a most unusual character in Rhipsalis. Unfortunately, his description and drawing, based on Weberbauer's preserved specimen, failed to show the length of the tube or the distinctive floral limb.
Schumann (1903) had established a sub-genus of Rhipsalis, Acanthorhipsalis, for a single species, R. monacantha, basing it solely on the presence of prominent stem spines. Britton and Rose (1923) raised this subgenus to generic rank, adding A. crenata and A. micrantha and citing the last species as the type. Aside from Hunt (1967) and Vaupel, Acanthorhipsalis has been upheld as a genus by all other cactologists, though without agreement as to the characters on which it should be based.
The unique floral characters of A. micrantha were not recognized until plants collected at the type locality by the Peruvian botanist, C. Vargas, arrived in flower at the University of California Botanic Garden, Berkeley, in September, 1959. These flowers were vastly different from those of any of its allies, for they were over an inch long, with purple tepals that expanded only apically and, most importantly, with a floral tube extending a centimeter beyond the pericarpel. Although the Vargas collection has been cultivated in California for the last twenty-four years, illustrations and a description of the distinctive characters of this species are being presented here in detail for the first time. The following description is based on the Vargas collection and on Vaupel's description of the fruit and seed.

Acanthorhipsalis micrantha (Vaupel) Britt. & Rose, Cact. 4: 211. 1923.
Cereus micranthus Vaupel, Jahrb. 50: Beibl. 111: 19. 1913.
Rhipsalis asperula Vaupel, Die Kakteen 2: 82. 1926.

Description given above
Specimens examined: Peru: Dept. Puno: Prov. Sandia: Sandia, on rocks at 2100 m. alt., July 31, 1902, Weberbauer 1353 (US, lectotype); on the outskirst of Sandia 1959, Vargas s. n., UCBG 59.1196, HBG 15928 and 33566 (HNT); near Sandia May 16, 1966, Ferreyra 16782 (MO).

In common with other primitive members of the subtribe Rhipsalidanae Britt. & Rose, A. micrantha has stems that are spiny, shrubby and erect-sprawling; only relatively long stems become pendent. The epidermis is roughened because of prominently convex surface cells, as indicated by its name under Rhipsalis, R. asperula; in no other member of the Rhipsalis alliance is this character so pronounced.
Small bracteoles and areolar wool are present on the pericarpel but the spine-like bristles found in Pfeiffera, Erythrorhipsalis and, often, in R. leucorhaphis are lacking; however, according to Vaupel, they sometimes appear on the fruit. The central and upper bracteoles, located above the pericarpel, are large, over-lapping and conspicuously petaloid, a character not found in Rhipsalis but similar to that present in Schlumbergera. Reddish purple floral color is also shared by A. micrantha, A. crenata, Hatiora herminiae, Rhipsalidopsis and Schlumbergera. The upper tepals are nearly parallel to the main floral axis, only the apices being expanded. Completely hidden by the overlapping central bracteoles is a receptacle tube extending 1 centimeter beyond the pericarpel, with the stamens becoming free only at the apex (see fig. 2). Elsewhere in the Rhipsalidanae, only Schlumbergera has a tube longer than 2 or 3 mm. In A micrantha the tube formation, red coloration and barely expanded limb indicate a modification for hummingbird pollination, which is typical for Schlumbergera but not for Rhipsalis, in which the flowers are
primarily bee-pollinated.
A. micrantha blooms sporadically over several months in spring, one or two flowers at a time, in contrast to the usual profuse flowering of Rhipsalis. Each flower also persists (uniquely in this alliance) five or six days before closing. Fruit has never set spontaneously during the twenty-four years I have been growing this species, nor has it formed after pollination by its nearest allies, R. paranganiensis and monacantha.
The cultivation of A. micrantha presents some difficulties. As its saxicolous manner of growth indicates a need for good drainage, A. micrantha would seem an ideal subject for basket culture except that its stiff growth-habit does not result in a very graceful specimen. I have been growing two plants in the green-house at the Huntington for many years in four-inch plastic pots, considerably underpotted considering that the stems are over three feet long; these same plants lost their roots when transferred to larger pots. Because of the alkaline water of southern California, I have used only distilled water on this and other difficult-to-grow epiphytic cacti. The plants of A. micrantha have grown slowly but flower each spring. Elmer Lorenz of Los Angeles, a noted collector of epiphytic cacti, has grown this same clone in a basket hung outdoors under shading cloth; it has grown well, but has never flowered. Perhaps the heat of a glass-house and suppressed vegetative growth encourage regular flowering in this species.
Evidence to support this theory was noted during the drawing of the accompanying plate. In July, 1982, a ten-inch cutting was given to the artist, who stored it intermittently with the drawing in a closed metal cabinet. After two months a flower bud emerged from the stem and, a week later, developed into a fully opened flower, though it was slightly paler and smaller than normal. A month later another, slightly smaller, flower opened on the non-yellowing and shrivelled cutting. These flowers had developed on a severed stem in spite of (or perhaps because of three months in a completely darkened cabinet.
Though it lacks the attractive pendent growth-habit of most Rhipsalis species, Acanthorhipsalis micrantha is well worth growing for its remarkable flowers. It should become widespread in collections following the International Succulent Institute's distribution of the Vargas collection in 1980.