13. Tithymalus Rob˙stus (Engelm.) Small. Rocky Mountain Spurge

Fig. 2765

Euphorbia montana β robusta Engelm. Bot. Mex. Bound.

Surv. 192. 1859. E. robusta Small, in Britt. & Brown, 111. Fl. 2: 381.

1897.

Perennial by a perpendicular rootstock, glabrous, glaucous. Stems slender, clustered, erect or assur-gent,4'-14' tall, slightly angled, scaly below, branched, topped by a 3-5-rayed umbel; leaves, except the whorl subtending the umbel, scattered, ovate or oblong-ovate, 5"-8" long, thick, obtuse or apiculate, entire, sessile; bracts opposite, triangular-ovate or subreniform, involucres campanulate, 1 1/2" long, sessile, bearing 4 somewhat crescent-shaped unappendaged buff crenulate glands; capsule globose-ovoid, 2" long, horizontal, its lobes rounded; seeds oblong or obovoid-oblong, terete, 1 1/4" long, gray, minutely pitted.

Hills and plains, South Dakota to Montana, Wyoming, Nebraska, Arkansas and Arizona. May-Oct.

13 Tithymalus Rob Stus Engelm Small Rocky Mountain 1107