Key to Species

Joints cylindric; tubercles much flattened laterally. Fruit smooth or but slightly tuberculate.

Branches very stout, 5 cm. thick or more

Branches relatively slender, 2 cm. thick or less.

Plant glaucous; spines 4 at an areole

Plant not glaucous; spines more than 4 at an areole

Fruit manifestly tuberculate.

Tall species, up to 2 or 4 meters high.

Flowers small; petals 1.5 cm. long

Flowers large; petals 2 to 3 cm. long

Low species, 6 dm. high or less.

Flowers yellow

Flowers rose-colored

Joints clavate; tubercles not much flattened laterally

22. Opuntia cholla Weber, Bull. Mus. Hist. Nat. Paris 1: 320. 1895.

Usually tree-like, 1 to 3 meters high, with a definite trunk 7 to 15 cm. in diameter; trunk very spiny at first and becoming more spiny each year for some time, but in age spineless and developing a smooth, brownish yellow bark; top of plant often dense and broad; joints often in whorls, horizontal, pale, with large compressed tubercles; spines usually numerous, more or less porrect, covered with loose brownish sheaths; glochids numerous, yellow; flowers rather small, 3 cm. broad, deep purple; fruit often 4 to 5 cm. long, usually proliferous, often in long chains of 8 to 12 individuals or forming compound clusters; seeds numerous, very small, often abortive.

.23. O. calmalliana .24. O. versicolor

.26. O. imbricata

Type locality: In Lower California.

Distribution: Lower California.

This is one of the commonest opuntias in southern Lower California and was usually seen by Dr. Rose at every locality visited south of Magdalena Bay on the west coast and on the east coast as far north as Muleje. It is undoubtedly the plant referred to O. prolifera by Mr. Brandegee, but it differs in habit and armament from that species; the fruit of O. prolifera is nearly or quite devoid of seeds, while this species often has numerous small ones. In this species, as in a few other opuntias, the fruits are quite proliferous, hanging on for a number of years and usually remaining green. They are, however, easily detached, and on falling to the ground, readily take root and start new colonies. Our illustration shows some of the fruits which have already rooted and have developed young joints.

The plant here described is the true "cholla" of the people of Lower California, and is the plant cultivated under that name by A. Berger at La Mortola from a cutting of Weber's type specimen, and by the late Mr. Darrah at Manchester, England.

Illustrations: Contr. U. S. Nat. Herb. 16: pl. 128, a; Karsten and Schenk, Vegetationsbilder 13: pl. 17, B.

Figure 73 is from a photograph of a plant collected by Dr. Rose at Cape San Lucas; figure 74 represents a joint of the same plant; figures 75 and 76 represent its proliferous fruits developing new joints.

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