THE CACTACEAE. 



Order CACTALES. 



Perennial, succulent plants, various in habit, mostly very spiny, characterized by specialized 

 organs termed areoles. Leaves usually none, except in Percskia and Pereskiopsis, where they are 

 large and flat but fleshy, and in Opuntia and its relatives, where they are usually much reduced 

 and mostly caducous, terete, or subulate. Spines very various in size, form, arrangement, and 

 color, sometimes with definite sheaths. The areoles are peculiar and complex organs, situated in 

 the axils of leaves when leaves are present, and bearing the branches, flowers, spines, glochids, hairs, 

 or glands; in some genera two kinds of areoles occur, either distinct or united by a groove. Flowers 

 usually perfect, either regular or irregular, usually solitary but sometimes clustered, sometimes 

 borne in a specialized terminal dense inflorescence called a cephalium; perianth-tube none, or large 

 and long, the limb spreading or erect, short or elongated, the lobes few or numerous, often inter- 

 grading in shape and color, but sometimes sharply differentiated into sepals and petals; stamens 

 commonly numerous, elongated or short, sometimes clustered in series, the filaments usually borne on 

 the throat of the perianth, the small oblong anthers 2-celled; style one, terminal, short or elongated; 

 stigma-lobes 2 to many, usually slender; ovary i -celled, distinct, or immersed in a branch or 

 forming a part of a branch ; ovules numerous. Fruit a berry, often juicy and sometimes edible, 

 sometimes dry, in one species described as capsular and dehiscing by an operculum, in others opening 

 by a basal pore. Seeds various; cotyledons two, accumbent, sometimes minute knobs, often broad 

 or elongated; endosperm little or copious; radicle terete. 



The 'order consists of the following family only : 



Family CACTACEAE Lindley, Nat. Syst. ed. 2. 53. 1836. 

 Characters of the order as given above. The family is composed of three tribes. 



KEY TO TRIBES. 



Leaves broad, flat; glochids wanting; flowers stalked (sometimes short-stalked), often clustered i. Pereskieae 



Leaves (except in Pereskiopsis) terete or subterctc, usually small, often wanting on the vegetative parts; 



flowers sessile. 

 Areoles with glochids (except in Maihuenia)', vegetative parts bearing leaves, which are usually 



small and fugacious; flowers rotate (petals erect in Nopalea) 2. Opuntieae 



Areoles without glochids; usually no leaves on the vegetative parts (except cotyledonary) ; flowers 



with definite tubes (except Rhipsalis) 3. Cereeae 



Tribe 1. PERESKIEAE. 



.Stems and foliage as in other dicotyledonous plants; inflorescence in some species compound; 

 flowers more or less stalked, their parts all distinct; glochids wanting; ovule with short funicle; 

 testa of seed thin, brittle. 



The genus Percskia, the only representative of this tribe, is, on account of its similarity 

 to other woody flowering plants, considered the nearest cactus relative to the other families, 

 but this relationship is in all cases remote. 



The nearest generic relatives of Percskia in the cactus family are doubtless the following: 



Pereskiopsis, some of whose species were first assigned to the genus Percskia, but they 

 have different foliage and the areoles often bear glochids. 



( ipitntia, whose species have leaves, though much reduced and usually caducous, other- 

 wise very different; but some of the species of Opnntia were first referred to Percskia. 



Maihuenia (two of whose species have only recently been taken out of Pcreskid), whose 

 seeds are similar but the areoles lack glochids, otherwise very different. 



This tribe has a wide geographic distribution, but is found wild only in the tropics. 



1. PERESKIA (Plumier) Miller, Card. Diet. Abr. ed. 4. 1754. 



Leafy trees, shrubs, or sometimes clambering vines, branching and resembling other woody 

 plants; spines in pairs or in clusters in the axils of the leaves, neither sheathed nor barbed; glochids 

 (found only in the Opuntieae) wanting; leaves alternate, broad, flat, deciduous, or somewhat fleshy; 

 flowers solitary, corymbose, or in panicles, terminal or axillary, wheel-shaped; stamens numerous; 

 style single ; stigma-lobes linear; seeds black, glossy, with a brittle shell, the embryo strongly curved ; 

 the cotyledons leafy; seedlings without spines. 



