GENUS 19. 



ROSE FAMILY. 



265 



i. Sanguisorba canadensis L. American 

 Great Burnet. Fig. 2264. 



Sanguisorba canadensis L. Sp. PI. 117. 1753. 

 Poterium canadense A. Gray, Man. Ed. 5, 150. 1867. 



Glabrous or slightly pubescent toward the base, 

 erect, simple, or branched above, i-6 high, the 

 branches erect. Stipules often foliaceous and 

 dentate; basal leaves long-petioled, sometimes 2 

 long; leaflets 7-15, ovate, oblong, or oval, obtuse 

 or acutish, cordate or obtuse at the base, serrate 

 with acute teeth, stalked, i'-3' long; flowers 

 white, perfect, bracteolate at the base, in dense 

 terminal showy spikes i'-6' long; stamens 4; fila- 

 ments long-exserted, white; achene enclosed in 

 the 4-winged calyx. 



In swamps and low meadows, Newfoundland to 

 Michigan, south to Georgia. July-Oct. 



Sanguisorba officinaiis L., native of Europe and 

 Asia, found in fields in Maine and recorded from 

 Minnesota, differs in having purplish flowers with 

 short stamens not longer than the sepals. 



20. POTERIDIUM Spach, Ann. Sci. Nat. III. 5 : 43. 1846. 



Annual or perennial herbs, with branched stems, stipulate, odd-pinnate leaves, the leaf- 

 lets pinnatifid, and greenish perfect bracted flowers in dense oblong spikes. Calyx-tube 

 urn-shaped, constricted at the mouth, 4-winged, its 4 lobes with scarious margins. Stamens 

 2 or 4; filaments short. Pistil i; style terminal; stigma brush-like; ovule I, suspended. 

 Achene enclosed in the dry calyx-tube. [Greek, diminutive of Poterium.] 



Two species, one of northwestern America and the following typical one. 



i. Poteridium annuum (Nutt.) Spach. Plains 

 Poteridium. Fig. 2265. 



Poterium annuum Nutt. ; Hook. Fl. Bor. Am. i : 198. 1832. 

 Sanguisorba annua Nutt. ; T. & G. Fl. N. A. i : 429. 1840. 

 Poteridium annuum Spach. Ann. Sci. Nat. III. 5 : 43. 1846. 



Glabrous, 4'-is' high. Leaflets 7-15, broadly obovate, 

 6" long or less, pectinate-pinnatifid, with linear-oblong 

 segments; spikes ii' long or less, about 3^" thick; 

 bracts ovate, shorter than the flowei-s ; calyx-lobes oval, 

 apiculate, i" long; stamens usually 4; fruiting calyx- 

 tube strongly 4-winged. 



Plains, Kansas to Arkansas and Texas. Summer. 



21. POTERIUM L. Sp. PI. 994. I753- 



Perennial herbs, with odd-pinnate, stipulate leaves, and small, perfect and imperfect 

 flowers in dense heads. Calyx-tube 4-angled, constricted at the thrpat, 4-lobed. Petals 4. 

 Perfect flowers with several or numerous declined stamens, the filaments capillary. Pistils 

 2; style terminal; stigmas brush-like. Achene enclosed in the thickened, 4-angled calyx- 

 tube. Seed suspended. [Greek, goblet or beaker.] 



About four species, natives of the Old World, the following typical. 



