Aruncus dioicus var. vulgaris
J. Jap. Bot. 30: 68. 1955.
Leaf surfaces usually glabrous. Styles 0.3–0.5 mm. Follicles slender, 2.5–3 mm. Seeds 1.8–2.5 mm. 2n = 14, 18.
Phenology: Flowering summer.
Habitat: Rich woods
Elevation: 10–500 m
Introduced; N.S., Ont., Que., Conn., Del., Maine, Mich., N.J., N.Y., Wis., c Europe, Asia (Caucasus)
Variety vulgaris seems to be introduced and locally naturalized in the North America. The variety differs very little from var. acuminatus and may prove to be identical. The longer follicles of var. acuminatus seem to be the only difference, though H. Hara (1955) said that the petals of var. vulgaris are larger than those of the other varieties. One may wonder whether this European-Asian taxon is a westward circum-Pacific extension of the American var. acuminatus, or whether the latter is an eastward extension of var. vulgaris. Aruncus dioicus in the broad sense displays the classic Arcto-Tertiary Mesoflora distribution pattern, and it is impossible to say where it originated, though the greatest diversity of varieties (ten) is in eastern Asia (Hara). The names A. aruncus (Linnaeus) H. Karsten and A. vulgaris Rafinesque are invalid and linked to this variety.
"thick" is not a number.