Perennial herb 30 - 80 cm tall Stem: erect, hairless below, but the upper part with short, less than 0.5 mm long, appressed hairs. Leaves: alternate, stalked (though stalks mostly shorter than the inflorescence branches), normally wider than long, 10 - 20 cm long, somewhat triangular in outline, but deeply pinnately divided (almost to the midvein) into five, somewhat lance-shaped segments, with sharp, pointed tips, and sharp, ascending teeth on the edges. The terminal lobe and basal pair of lobes are often further two- to three-lobed. Inflorescence: of very dense, compact, rounded, branched clusters on long (longer than the leaf stalks), forked stalks arising from the upper leaf axils. The inflorescence branches, as well as the individual flower stalks, have short, appressed, ascending hairs. Flowers: short-stalked, white to pale purple, 0.7 - 1 cm long, radially symmetric, and tubular. Sepals: five, but fused at the very base, then separating into narrowly linear, sparsely stiff-hairy lobes with long, slender bristles along the edges. Petals: five, but fused for over half their length, then separating into shorter, erect, flat-tipped lobes. Five linear nectaries line the inside of the petal tube opposite each petal lobe. Stamens: five, filaments hairy, attached near the base of the petal tube (between the linear nectaries), alternating with the petal lobes, and extending far beyond the petals. Pistil: with a single-chambered, superior, bristly ovary; and a single style ending in two, short, rounded stigmas, which reach far beyond the petals. Fruit: a spherical, single-chambered, two-valved capsule with one to three seeds. Roots: fleshy, fibrous, with a long, scaly rhizome.
Similar species: Hydrophyllum virginianum is similar to H. appendiculatum, but that species has the stem and inflorescence branches densely covered with a mixture of both short (up to 0.5 mm long) and long hairs (2 - 3 mm long), the main inflorescence stalk does not fork, and there are large earlobe-shaped appendages alternating the base of each sepal lobe. Also somewhat similar is H. canadense, but that species usually has the leaves over-topping the inflorescence, the sepal lobes are mostly hairless and sometimes have a small upright tooth alternating between them, the stem hairs are up to 1 mm long, and the inflorescence branches are mostly hairless. Our plants of H. virginianum are the typical variety with white to lavender or pale purple flowers, but H. virginianum var. atranthum, which occurs in the southern Appalachians, has deep violet flowers, and leaves often with seven to nine segments.
Flowering: early May to mid-June
Habitat and ecology: Common in woods throughout the Chicago Region, and able to tolerate some level of disturbance.
Occurence in the Chicago region: native
Author: The Field Museum
From Flora of Indiana (1940) by Charles C. Deam
Infrequent throughout Indiana except the southwestern part. It prefers moist soil in woodland, although it is sometimes found along roadsides and railroads. Usually found in alluvial flood plains and in moist woods of nearly any composition, although it is more frequent in beech and sugar maple and white oak woods.
Stems 3-8 dm, the upper part, pedicels, and sep with appressed or ascending hairs rarely to 0.5 mm; cauline lvs broadly ovate or broadly triangular in outline, 1-2 dm and usually somewhat wider, pinnately divided almost to the midvein, the segments usually 5(7-9), the terminal one and the basal pair often 2-3-lobed, all with sharply acute or acuminate apex and similar, strongly ascending teeth; infls dense at anthesis; sep sparsely hirsute-ciliate; cor 7-10 mm; stamens and style long- exsert; 2n=18. Moist or wet woods, or open wet places; Que. to N.D., s. to N.C., Ala., and ne. Okla. May, June. The widespread var. virginianum has white to lavender or pale purple fls. Var. atranthum (Alexander) Constance, of the s. Appalachians from Va. and W.Va. to N.C., has deep violet fls and often has 7-9 lfls.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.