220 THE CACTACEAE. 
supposedly distinct species have been described by authors from tropical Africa, and 
R. cassutha has long been known to exist in Ceylon. M. Roland-Gosselin, a diligent 
French student of cacti, after an investigation of these Old World plants, published in 1912 
a very interesting paper,* giving his conclusion that they are really all American species, 
their seeds having been transmitted to the Old World by migratory birds, and he referred 
them all to known American species. We have followed him in these reductions but we 
have not been able in all cases to study authentic specimens. It raises the interesting 
question if the Old World plants should be regarded as native or introduced. 
In stem structure some of the species, such as Rhipsalis elliptica, approach very closely 
Zygocactus truncatus, while certain forms of Epiphyllanthus are easily mistaken for a Rhipsalis. 
As we have treated the genus here, the flowers and fruits are fairly uniform. The stem 
structures are various and parallel in a way those of Opuntia, ranging from slender and 
terete to broad and thin; in some species they are leaf-like as in Epiphyllum, or 3-angled, 
suggesting Hylocereus. The areoles are usually small and bear only a small tuft of wool, 
but in some species they bear hairs or bristles. The flowers may open at any time of the 
day and in most species do not close at the approach of night; they are not readily affected 
by shade or direct sunlight and open but once. 
KEy TO SPECIES. 
A. Joints terete, ribbed or angled, none of them flat. 
B. Joints terete or young ones angled, smooth, or areoles bristly or hairy. 
C. Joints short, oblong, not more than 5 times as long as thick; areoles of young 
joints with a few long hairs. : 
Lateral joints simple; flowers lateral. Series 1, Mesembryanthemoides.... 1. R. mesembryanthemoides 
Lateral joints much branched; flowers terminal. Series2, Cereusculae..... 2. R. cereuscula 
CC. Jvints cylindric, rarely clavate, slender, short or elongated. 
D. Flowering areoles small, not very woolly, not depressed. 
E. Ultimate jointsslender, about 2.5 mm. thick or less, relatively short. 
F. Young joints or some of them angled, their areoles bearing 
; hairs. Series 3, Prismaticae. 
, 
Species of Brazil or Madagascar................0c0e00ee 3. R. prismatica 
Species of Costa Rica... 2.0... 0. occ ee eee eens 4. R. simmlert 
FF. All joints cylindric to clavate. Series 4, Capilliformes. 
Joints clavate... 0... cece ee ccc cece eeees 5. R. clavata 
Joints cylindric. 
Ultimate joints up to 2.5 mm. thick; petals 9 mm. long:. 6. R. campos-portoana 
Ultimate joints about 1.5mm. thick; petals 6 mm. long or less. 
Plant stiff; areoles red; flowers white................ 7. R. heteroclada 
Plant weak; areoles not red. 
Flowers greenish white or yellowish, 5to6mm. wide. 8. R. capilliformis 
Flowers white or nearly white, about 8 mm. wide. 
Pendent; secondary branches 2 to 3-chotomous..... 9. R. burchellit 
é . Spreading or diffuse ; upper branches subverticillate. 10. R. cribrata 
EE. Ultimate joints stouter, mostly 3 to 10 mm. thick and elongated. 
F. Scale subtending the areoles inconspicuous or none. 
G. Ultimate joints 3 to 6 mm. thick. Series 5, Cassuthae. 
H. Ultimate joints definitely shorter than others, often 
verticillate. : 
Plants weak, pendent.................00000000. 11. R. cassutha 
, Jol eseeeeeeeeseeee 12, R. virgata 
Ultimate joints stout.........000.0.......0.. 13. R. teres 
Fruit naked 
Petals pink.........00 00000000... .0 000. 14. R. lindbergiana 
Petals white.......................... 15. R. shaferi 
Fruit with scales and these setose in axils... 16. R. fasciculata 
Petals 8 to 12 mm. long. 
Flowers purplish red; areoles not bristly.... 17. R. pulchra 
Flowers white; areoles somewhat bristly.... 18. R. lumbricoides 
* Bull. Soc. Bot. France 59: 97-102. 1912. Translation in Torreya 13: 151-156. 1913. 
