Tetradymia. composite. 447 



164. TETRADYMIA. DC. prodr. 6. p. 440; Deless. ic. 4. t. 60. 

 Tetradpnia & Lagotliamnus, Nutt. 



Heads 4- or sometimes 5-9-flowerecl ; the flowers all tubular and perfect. 

 Involucre of 4 or 5 (rarely 6) oval or oblong and obtuse coriaceo-charta- 

 ceous carinate-concave scales, somewhat in two series. Receptacle small, 

 naked. Corolla with a slender tube and a deeply 5-cleft limb ; the lobes 

 linear, spreading, mostly furnished with an indistinct mid-nerve. Anthers 

 exserted. Branches of the style tipped with a very short and obtuse pube- 

 rulent cone. Achenia oblong, terete, villous with long and soft denticulate 

 hairs. Pappus at first shorter than the corolla, composed of numerous 

 strongly denticulate and rather rigid unerjual capillary bristles. — Herbaceous? 

 or shrubby canescently tomentose branching plants (natives of dry barren 

 plains in and near the Rocky Mouniains) ; the leaves linear, entire, sessile, 

 alternate, often fascicled; the primary frequently converted into spines. 

 Heads corymbose or racemose, and often clustered at the extremity of the 

 branches, rather large. Flowers bright yellow. 



§ 1. Involucre of 4-5 scales, 4-flowered : the villous hairs of the achenia 

 much shorter than the very copious pappus. — Eutetradtmia. 



1. T. canescens (DC.) : herbaceous? unarmed ; silvery-tomentose ; leaves 

 scattered on the simple stems or branches, narrowly linear, rather rigid, mu- 

 cronate ; peduncles as long as the racemose-corymbose heads ; scales 

 of the involucre 4. — DC. ! in Deless. ic. sel. 4. t. 60, S^ prodr. I. c. ; Hook. A* 

 Arn. ! hot. Beechey, suppl. p. 360. 



Interior of Oregon or CaHfornia, Douglas! — Leaves an inch and a half 

 long, scarcely a line wide, none of them fascicled or spinescent. Flowers 

 fully half an inch long. Hairs of the achenia, as in all the species of tliis 

 section, as long as or longer than the achenium, and strongly denticulate 

 under a lens, especially the uppermost, which might readily be confounded 

 with the pappus. 



2. T. inermis (Nutt.) : shrubby, much branched, unarmed, silvery-canes- 

 cent ; leaves thickish, short, linear-lanceolate or somewhat spatulate, obtuse 

 or mucronulate-acute, either scattered or fascicled ; heads corymbose-clus- 

 tered, on short peduncles; scales of the involucre mostly 4. — Nutt..' in trans. 

 Amer. phil. sac. (n. ser.) 7. p. 415. 



Dry barren plains west of the Rocky Mountains, particularly near Lewis 

 River, Nuttall! Also east of the Rocky Mountains on hills of the upper 

 part of the North Fork of the Platte, near Deer Creek ; and on the Wind 

 River Chain at the height of 7000 feet, Lieut. Fremont! Aug. — Shrub 1-3 

 feet high, not spinescent. Leaves 6-9 lines long, 1-2 wide, canescent with 

 a close tomentum. Heads and flowers smaller than in the preceding spe- 

 cies; to which some states are very closely allied. 



3. T. Nuttallii : shrubby, much branched, woolly when young, canes- 

 cent; primary leaves mostly converted into subulate spines; the others 

 densely fascicled in their axils, thickish, linear-sjjatulate, obtuse, the tomen- 

 tum somewhat deciduous ; heads fascicled and in corymbose clusters, on 

 very short peduncles ; scales of the involucre 4-5. — T. spinosa, Nutt. ! I. c, 

 not of Hook. Sf Arn. 



