Astilbe biternata

Leaves coarse, terminal leaflets usually 3-lobed, or at least 2-lobed, even if weakly or unevenly; petiole, rachis, and petiolules usually stipitate-glandular. Leaflets petiolulate; blade ovate, 8-15 × 4-15 cm, base usually cordate, rarely cuneate, margins sharply serrate to crenate, apex acuminate. Flowers: sepals persistent, triangular, 0.7-1.5 mm; petals 5 or absent in pistillate flowers, erect, spatulate to subulate, 1.5-4 mm. Capsules partly connate, or separating as 2 follicles, 3.5-4 mm. Seeds 5-10, linear, 1.5-2 mm. 2n = 28.

Flowering Jun. Rich woods and shaded north-facing road banks, ditches and seeps; 300-1200 m; Ga., Ky., N.C., S.C., Tenn., Va., W.Va.

Astilbe biternata is known from the southern Appalachian Mountains from Mingo County, West Virginia, through Virginia and Kentucky to the Carolinas, Tennessee, and northwestern Georgia.

Elegant when in flower, although rarely cultivated, Astilbe biternata is often confused with goat´s-beard, Aruncus dioicus (Walter) Fernald (Rosaceae), which grows in identical habitats and often side-by-side. Remarkably, both are dioecious with relatively large compound leaves and terminal panicles of relatively small, white, unisexual flowers. Elsewhere in the world, Astilbe species generally have bisexual flowers; Aruncus dioicus is dioecious around the world. Astilbe biternata flowers just after Aruncus, and may be further distinguished by its three-lobed terminal leaflets, glandular hairs, ten rather than 15 stamens, and usually two- rather than three-carpellate fruits.

Astilbe crenatiloba has been recognized from the rich, wooded lower slopes of the Tennessee side of Roan Mountain on the North Carolina-Tennessee border as being shorter, with crenate leaves, and fruits to 3 mm long. Although it seems to have distinctive features, it may be just a local variant. It is represented only by its original two herbarium specimens and has not been seen since its discovery, published in 1888, despite repeated searches.

Stems clustered on an enlarged caudex, 1-2 m, glandular hairy above; lvs petioled, 2 or 3 times ternately compound, the lfls sessile or petiolulate, oblong to ovate, rounded to subcordate at base, acuminate, sharply serrate; pet narrowly oblanceolate, 2 mm, often none in the pistillate fls; follicles connivent, 4 mm; 2n=28. Moist, north-facing woods in the mts., Va. and W.Va. to Ky., s. to Ga. June. Habitally much like Aruncus.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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