2 20 THE CACTACEAE. 



supposedly distinct species have been described by authors from tropical Africa, and 

 R. cassiiiha 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 oiEpiphyllanthiis are easily mistaken for aRhipsalis. 



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 Optintia, ranging from slender and 

 terete to broad and thin; in some species they are leaf-like as in Ep iphy Hum, or 3-angled, 

 suggesting Hylocereiis. 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 i, Mesembryaiithemaides . ... 1. R. mesemhryanthemoides 



Lateral jointsmuchbranched;flowers terminal. S<trie:5 2, Cereusculae 2. R. cereuscula 



CC. Joints cylindric, rarely clavate, slender, short or elongated. 

 D. Flowering areoles small, not very wooUy, not depressed. 



E. Ultimate joints slender, about 2.5 mm. thick or less, relatively short. 

 F. Young joints or some of them angled, their areoles bearing 

 hairs. Series 3, Prisinaticae. 



Species of Brazil or Madagascar i- R- prismatica 



Species of Costa Rica 4. R- simmleri 



FF. All joints cylindric to clavate. Series 4, Capillijormes. 



Joints clavate $■ R- clavala 



Joints c\lindric. 



Ultimate joints up to 2.5 mm. thick; petals 9 mm. long. . 6. R. campos-portoana 

 Ultimate joints about i .5 mm. thick ; petals 6 mm. long or less. 



Plant stiff; areoles red; flowers white 7. i?. heteroclada 



Plant weak; areoles not red. 



Flowers greenish white or yellowish, 5 to 6 mm. wide . 8. R. capilliformis 

 Flowers white or nearly white, about 8 mm. wide. 



Pendent;secondary branches 2 to 3-chotomous 9. R. burchellii 



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, CassiUkae. 

 H. Ultimate joints definitely shorter than others, often 

 verticillate. 



Plants weak, pendent 11. R- cassutha 



Plants stiffer, not strictly pendent. 



Ultimate joints slender 12. J?, virgala 



Ultimate joints stout i3- -R- t^i^es 



HH. Ultimatejointsnotdefinitelyshorterthanothers, sim- 

 ple or dichotomous, rarely verticillate. 

 I . Areoles without bristles or with spreading brisUes. 

 Petals about 4 mm. long. 

 Fruit naked 



Petals pink 14. R- lindbergiana 



Petals white 15- ^- shaferi 



Fruit with scales and these setose in axils ... 16. R. fascicidata 

 Petals 8 to 12 mm. long. 



Flowers purplish red; areoles not bristly. ... 17. i?. pulchra 

 Flowers white; areoles somewhat bristly. .. . 18. R. lumbricoides 



* Bull. Soc. Bot. France 59: 97-102. 1912. Translation in Torreya 13: 15 1-156. 1913. 



