Key to Species

Joints readily detached, turgid, some of them subterete or subglobose 216. O. fragilis

Joints not readily detached, usually flat and thin, or in O. arenaria sometimes turgid and nearly terete.

Joints turgid, usually small 217. O. arenaria

Joints thinner than the last, mostly flat, larger.

Spines, or some of them, very long, flexible and bristle-like.

Flowers 4 to 5 cm. long 218. O. trichophora

Flowers 5 to 6 cm. long 219. O. erinacea

Spines stiff, acicular or subulate; areoles distant. Spines subulate.

Fruit naked 220. O. juniperina

Fruit spiny.

Flowers yellow 221. O. hystricina

Flowers red 222. O. rhodantha

Spines acicular, slender; areoles close together.

Ovary and fruit without spines 223. O. sphaerocarpa

Ovary and fruit with spines 224. O. polyacantha

216. Opuntia fragilis (Nuttall) Haworth, Suppl. Pl. Succ. 82. 1819.

Cactus fragilis Nuttall, Gen. Pl. 1: 296. 1818.

Opuntia brachyarthra Engelmann and Bigelow, Proc. Amer. Acad. 3: 302. 1856.

Opuntia fragilis brachyarthra Coulter, Contr. U. S. Nat. Herb. 3: 440. 1896.

Opuntia fragilis caespitosa and tuberiformis Hortus, Stand. Cycl. Hort. Bailey 4: 2363. 1916.

(?) Opuntia columbiana Griffiths, Bull. Torr. Club 43: 523. 1916.

Usually low and spreading, small and inconspicuous, but sometimes forming mounds 2 dm high in the center and 4 dm. in diameter, with hundreds of joints; joints fragile (the terminal ones especially breaking off at the slightest touch), often nearly globular but sometimes decidedly flattened, usually dark green, 1 to 4 cm. long; areoles closely set, small, filled with white wool; spines 5 to 7, brown or only with brown tips and lighter below, 1 to 3 cm. long; glochids yellowish; flowers pale yellow, about 5 cm. broad; fruit dry, spiny, 1.5 to 2 cm. long, with a truncate or slightly depressed umbilicus; seeds large, 5 to 7 mm. broad.

Type locality: "From the Mandans to the mountains, in sterile but moist situations."

Distribution: Wisconsin to central Kansas and northwestern Texas, westward to Arizona, Oregon, Washington, and British Columbia.

Dr. Engelmann says "it is rarely found in flower and still more rarely seen in fruit." The only fruit we have seen was collected by Dr. Rose near Liberal, Kansas, in 19, 12.

Opuntia brachyarthra, sometimes regarded as a variety of O. fragilis, we regard as not specifically separable from that species. An examination of the type material now preserved in the Missouri Botanical Garden does not warrant a separation of any kind.

This species is of wide distribution and is especially common on the plains. It usually grows low, often being hidden by the grass. In the grazing country it is a most troublesome weed, for the joints easily break off and become attached by their spines to passing objects, thus greatly annoying and pestering all animals on the range, even frightening horses. The wide distribution of the species is doubtless largely due to the fact that the joints are so easily scattered. A hybrid with O. tortispina has been found in Kansas (Rose, No. 17132).

The plant is of especial interest as the most northern in distribution of the opuntias. It is stated that Opuntia cervicornis Späth (Cat. 156. 1906-7) is "probably a hybrid of which O. fragilis is a parent" (Kew Bull. Misc. Inf. 1907: App. 74. 1907). O. sabinii (Pfeiffer, Enum. Cact. 147. 1837) was given as a synonym of O. fragilis.

Illustrations: Cact. Journ. 1: 100; Dict. Gard. Nicholson 2: f. 752; Förster, Handb. Cact. ed. 2. f. 132; Gartenflora 30: 413; Pac. R. Rep. 4: pl. 12, f. 9; Rümpler, Sukkulenten f. 126; W. Watson, Cact. Cult. f. 78; Wiener Illustr. Gartenz. 10: f. 113, all as Opuntia brachyarthra. Illustr. Fl. 2: f. 2532; ed. 2. 2: f. 2991; Pac. R. Rep. 4: pl. 24, f. 5.

Plate xxxv, figure 1, shows old and young joints of the plant collected by C. Birdseye at Florence, Montana, in 1910. Figure 239 is from a photograph of the plant taken by E. R. Warren at San Acacio, Colorado, in 1912.

Fig. 239.—Opuntia fragilis.

217. Opuntia arenaria Engelmann, Proc. Amer. Acad. 3: 301. 1856.

Roots in clusters of 10 to 15, spindle-form, somewhat fleshy; stem prostrate, 2 to 3 dm. long, much branched; joints during growing season quite turgid, afterwards much thinner, 4 to 8 cm. long, half as broad as long; areoles large, numerous, filled with brown wool, glochids, and spines; spines 5 to 8 from an areole, 2 or 3 much longer than the others, sometimes 4 cm. long; flowers red, 7 cm. broad; fruit dry, spiny, 3 cm. long; seeds large, 7 cm. broad.

Type locality: Sandy bottoms of the Rio Grande near El Paso.

Distribution: Texas and southern New Mexico.

This species is very rare and has been reported only a few times. Dr. Rose, who has repeatedly collected at El Paso, was never able to find it until October 1913, and then but a single plant about 8 miles above El Paso on the New Mexican side of the Rio Grande. It grows in nearly pure sand not far above the level of the river.

BRITTON AND ROSE

PLATE XXXV

BRITTON AND ROSE

PLATE XXXV

1. Plant of Opuntia fragilis. 2. Flowering branch of Opuntia rhodantha. 3. Flowering joint of Opuntia polyacantha. (All natural size.)

Figure 240 is from a drawing of the plant collected by Dr. Rose near El Paso, Texas, in 1913.

218. Opuntia trichophora (Engelmann) Britton and Rose, Smiths. Misc. Coll. 50: 535. 1908.

Opuntia missouriensis trichophora Engelmann, Proc. Amer. Acad. 3: 300. 1856.

Opuntiapolyacantha trichophora Coulter, Contr. U. S. Nat. Herb. 3: 437. 1896.

A low, spreading plant, often forming small clumps 6 to 10 dm. in diameter; joints orbicular to obovate, 6 to 10 cm. in diameter; areoles closely set; spines numerous, very unequal, the longer one 4 cm. long or so, acicular, pale, often white, but on old joints developing into long, weak hairlike bristles; flowers yellow, the sepals tinged with red; ovary with numerous areoles, these bearing weak, pale bristles; fruit unknown.

Type locality: Mountains near Albuquerque, New Mexico.

Distribution: New Mexico, Texas, and Oklahoma.

This plant, while closely related to Opuntia polyacantha, seems worthy of specific rank, its long weak spines being apparently characteristic. Its northern extension into Oklahoma has recently been determined from plants collected by G. W. Stevens.

Illustrations: Pac. R. Rep. 4: pl. 15, f. 1 to 4; pl. 23, f. 19, all as Opuntia missouriensis trichophora.

Figure 241 is copied from the first illustration above cited.

Fig. 241.—Opuntia trichophora. X0.75.

Fig. 241.—Opuntia trichophora. X0.75.

219. Opuntia erinacea Engelmann, Proc. Amer. Acad. 3: 301. 1856.

Opuntia ursina Weber, Dict. Hort. Bois 896. 1898.

Growing in small, low clumps, the branches ascending or erect; joints ovate to oblong, flattened or thick, sometimes nearly terete, 8 to 12 cm. long; areoles somewhat tuberculate, large, numerous, closely set, 4 to 10 mm. apart; spines numerous, usually white or sometimes brownish or with brown tips, slender, often 5 cm., sometimes 12 cm. long or even more, stiff, often developing on the old joints as long hairs or bristles; glochids numerous; flowers rather large, 6 to 7 cm. long, either red or yellow; ovary and fruit very spiny; seeds large, rather regular.

Type locality: On Mojave Creek, California.

Distribution: Northwestern Arizona, southern Utah, California.

southern Nevada, and eastern

This species has long been passing under the name of Opuntia rutila Nuttall (Torrey and Gray, Fl. N. Amer. 1: 555. 1840). Dr. Engelmann referred it there in the Report of Simpson's Expedition (page 442), and again in the Botany of California, with the remark that "this plant seems to be Nuttall's long lost O. rutila." And while it is true that the identification of Nuttall's plant is still doubtful, it seems improbable that this reference is correct, for the

Fig. 242.—Opuntia erinacea.

description does not agree with that of the above, and the original station of O. rutila in Wyoming is far removed from the other; keen collectors like A. Nelson and V. Bailey, who have searched for the plant for us, have failed to find it in Wyoming. We suspect that O. rutila will prove to be O. polyacantha.

Opuntia ursina, which comes from the Mojave Desert, seems to be only a slender form with long weak spines. This is known in the trade as the California grizzly bear cactus. Alverson has described it as follows: "This curious plant is covered with tawny white hairs or flexuous spines, some of which are from 3 to 6 inches long, and I have some extra fine specimens with the spines or hairs 9 and 12 inches long."

Illustrations: Alverson, Cact. Cat. 9 as Opuntia ursina; Pac. R. Rep. 4: pl. 13, f. 8 to 11; pl. 24, f. 4.

Figure 242 is from a photograph of the plant taken by T. B. Headley at a point about 29 miles east of Fallon, Nevada, in 1910.

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