Great burnet, burnet-bloodwort

Poterium officinale (Linnaeus) A. Gray; Sanguisorba microcephala C. Presl; S. officinalis subsp. microcephala (C. Presl) Calder & Roy L. Taylor

Plants 3–20 dm. Leaves: blade 5–40 cm, leaflets (7–)11–15, orbiculate to ovate, to 7 × 5 cm, lengths 1.5–2.5 times widths, base cuneate, truncate, rounded, or cordate, without stipels. Spikes 50–250-flowered, ellipsoid or ovoid, main 1.5–3 cm, flowering basipetal. Flowers: calyx lobes dark purple, midveins not thickened distally; stamen lengths ± equal to hypanthium lobes, filaments 1.5–2.5 mm, filiform throughout. 2n = 56, 112.

Flowering (Jun–)Jul–Sep; fruiting Aug–Oct. Muskeg, fens, bogs, swamps, tundra, stream banks (especially in ice-scoured areas), often on serpentine rock; 0–1600 m; B.C., N.W.T., N.S., Yukon; Alaska, Calif., Maine, Mich., Oreg., Pa., Wash.; n Europe; n Asia.

Occurrences of Sanguisorba officinalis in eastern North America represent introductions from Eurasia; the species is native in western North America. Near the southern end of its distribution in western North America, the species is generally found over serpentine substrates. There seem to be no consistent differences upon which to base a taxonomic distinction at any level between native northwestern North American plants (S. microcephala) and Eurasian S. officinalis in the strict sense.

SELECTED REFERENCE Nordborg, G. 1963. Studies in Sanguisorba officinalis L. Bot. Not. 116: 267–288.