1. Mamillaria. Globose or oval plants, covered with spine-bearing tubercles. Flowers from between the tubercles. Ovary naked; berry succulent.
2. Opuntia. Branching or jointed plants; the joints flattened or cylindrical.
Flowers about as long as wide, the tube campanulate or funnel-shaped. Ovary often hidden between the bases of the tubercles, naked, the succulent berry exserted. Seeds yellowish-brown to black, crustaceous.—Globose or oval plants, covered with spine-bearing cylindrical, oval, or conical tubercles, the flowers from distinct woolly or bristly areoles at their base. (Name from mamilla, a nipple, referring to the tubercles.)
1. M. vivípara, Haw. Simple or cespitose, 1–5´ high, the almost terete tubercles bearing bundles of 5–8 reddish-brown spines (10´´ long or less), surrounded by 15–20 grayish ones in a single series, all straight and very rigid; flowers purple, with lance-subulate petals and fringed sepals; berry oval, green; seeds pitted, light brown.—Plains of Dak. to Kan., and westward.
2. M. Missouriénsis, Sweet. Smaller, globose, with fewer (10–20) weaker ash-colored spines; flowers yellow, 1–2´ broad; berry subglobose, scarlet; seeds few, black, pitted. (M. Nuttallii, Engelm.)—S. Dak. to central Kan., Tex., and westward.
2. OPÚNTIA, Tourn. Prickly Pear. Indian Fig.
Sepals and petals not united into a prolonged tube, spreading, regular, the inner roundish. Berry often prickly. Seeds flat and margined, covered with a white bony arillus. Embryo coiled around albumen; cotyledons large, foliaceous in germination.—Stem composed of joints (flattened in ours), bearing very small awl-shaped and usually deciduous leaves arranged in a spiral order, with clusters of barbed bristles and often spines also in their axils. Flowers in our species yellow, opening in sunshine for more than one day. (A name of Theophrastus, originally belonging to some different plant.)
[*] Spines small or none; fruit pulpy.
1. O. vulgàris, Mill. Prostrate or spreading, light green; joints broadly obovate (2–4´ long); leaves minute (2–2½´´ long), ovate-subulate, generally appressed, bristles short, greenish yellow, rarely with a few small spines; flowers pale yellow (about 2´ broad), with about 8 petals; fruit 1´ long.—Sandy fields and dry rocks, Nantucket to S. C., near the coast; Falls of the Potomac.