18Q ROSACEA. Acaena. 



21. AC.S1NA, Linn. 

 Calyx-tube oblong, persistent, contracted at the throat, at length armed with 

 retrorsely barbed prickles ; limb 3 - 7-parted, valvate, deciduous. Petals none. 

 Stamens 1 to 10, usually 3 to 5. Carpels 1 or 2, free from the calyx: style ter- 

 minal : stigma capitate and multitid : ovule solitary, suspended. Akene enclosed 

 in the indurated calyx, membranaceous. — Perennial herbs, often woody at the de- 

 cumbent or creeping base ; leaves unequally pinnate, and leaflets incised or pinnati- 

 fld ; flowers in crowded spikes or heads. 



Species about 30, belonging largely to Chili and Peru, and almost exclusively to the temperate 

 and warmer regions of the southern hemisphere. There is a single Mexican species, besides the 

 following Chilian species in California. 



1. A. trifida, Buiz & Pavon. Silky-villous : stems erect from a woody caudex, 



3 to 15 inches high: leaves mostly crowded at the base; leaflets about 6 pairs, 

 nearly uniform, oblong-ovate, 3 to 5 lines long, pinnately cleft into 3 to 7 segments : 

 flowers green, in a cylindrical crowded spike, the lower often remote : calyx-lobes 

 li lines long, exceeding the tube: spreading stamens purple; filaments exserted : 

 fruit ovate, 2 lines long, 3 - 4-angled ; angles armed with 2 to 4 stout prickles, and 

 shorter ones in the intervals : akene round-oblong. — Fl. Peruv. i. 67, t. 104. A. 

 pinnatifida, Hook. & Arn. Bot. Beechey, 339, not Euiz & Pavon; Torr. & Gray, 

 Fl. i. 430 ; Torrey, Bot. Mex. Bound, t. 19. 



Dry hill s in the Coast Eanges, from Monterey to Marin Co. 



22. POTERIUM, Linn. Burnet. 



Calyx-tube turbinate, contracted at the throat, persistent, becoming 3 -4-angled 

 or winged and thickish ; limb 4-parted, imbricate in the bud, petal-like, deciduous. 

 Petals none. Stamens 4 to 1 2 or more ; filaments often elongated. Carpels 1 to 3, 

 free from the calyx : style terminal, filiform : stigma tufted : ovule solitary, sus- 

 pended. Akene enclosed, membranaceous. — Herbs, mostly perennial ; leaves pin- 

 nate, with coarsely toothed petiolulate leaflets and foliaceous adnate stipules ; flowers 

 small, often polygamous or dioecious, bracteate and 2-bracteolate in a dense spike 

 upon a long naked peduncle. 



Species 15 or 20, of the temperate regions of the northern hemisphere. Besides the following 

 there is a single species in the Atlantic States, and a second in Alaska. 



1. P. officinale, Benth. & Hook. Perennial, usually glabrous, often 2 to 4 feet 

 high : leaflets about 4 pairs, ovate to oblong, cordate at base, \ to 2 inches long : 

 flowers deep purple or red, polygamous, in oblong spikes, a half to an inch long : 

 bracts often pubescent : stamens scarcely exserted : fruit a line long, equalling the 

 calyx-lobes. — Sanguisorba officinalis, Linn. S. microcephala, Presl in Ejrinielise 

 Bot. 202. 



Mendocino plains (Bolandcr) ; Oregon (Sail) ; Alaska, Kinnicut. Frequent in Europe and 

 Northern Asia. 



2. P. annuum, Nutt. Annual, glabrous, slender, 6 to 15 inches high : leaflets 



4 to 6 pairs, ovate to oblong, half an inch long or less, deeply pinnatifid ; segments 

 linear : flowers perfect, greenish, in ovoid to oblong heads, \ to 1 inch long : bracts 

 scarious, ovate, persistent, a line long : stamens 2 or 4, short : fruit shorter than the 

 bracts. — Hook. Fl. i. 198. Sanguisorba annua, Torr. & Gray, Fl. i. 429 ; Torrey, 

 Marcy Bep. 285, t. 5. S. myriophylla, Braun & Bouche, Ind. Sem. Berl. 1867, 10. 

 Poteridium annuum, Spach, Ann. Sci. Nat. 3 ser. v. 43. 



In the Sacramento Valley, Sarlwcg, Bolander. Also in the valley of the Columbia, on the 

 Upper Missouri, and in the Indian Territory. 



