Biennial herb 30 - 60 cm tall Stem: erect, densely hairy with short, slender hairs up to 0.5 mm long, and also with longer, 2 - 3 mm long, stiff, spreading hairs. Leaves: alternate, stalked (though stalks mostly shorter than the inflorescence branches), 6 - 15 cm wide, circular in outline, but very shallowly, palmately five- to seven-lobed, with wide bases between the lobes, and the lobe tips pointed. The lowest leaves are sometimes pinnately divided. All leaf bases inversely, broadly v-shaped, or cut abruptly straight across. Inflorescence: of loosely-flowered, rounded, branching clusters on long (mostly taller than leaves), densely hairy stalks arising from the upper leaf axils. The inflorescence branches, as well as the individual flower stalks, have a dense covering of intermixed short and long hairs. Flowers: slender-stalked, lavender or pinkish purple, 0.9 - 1.3 cm long, radially symmetric, and tubular. Sepals: five, but fused at the very base, then separating into narrow, densely bristly-hairy lobes. Alternating the base of each lobe is a conspicuous, 0.5 - 1.5 mm long, reflexed, earlobe-shaped appendage, which enlarges in fruit. Petals: five, but fused for about half their length, then separating into erect, oblong, flat-tipped lobes. Five linear nectaries line the inside of the petal tube opposite each petal lobe. Stamens: five, filaments usually hairy, attached near the base of the petal tube (between the linear nectaries), alternating with the petal lobes, and extending only a few millimeters beyond the petals. Pistil: with a single-chambered, superior, bristly ovary; and a single style ending in two, short, rounded stigmas, which extend a few millimeters beyond the petals. Fruit: a spherical, single-chambered, two-valved capsule with one to three seeds. The earlobe-shaped appendages at the base of the sepal lobes enlarge greatly in fruit. Root: a taproot.
Similar species: Hydrophyllum appendiculatum is similar to H. virginianum but that species has short, appressed, and ascending hairs on the inflorescence branches; the main inflorescence stalk forks into two; there are no appendages between the sepal lobes; and the stem hairs (if present) are appressed and under 0.5 mm long. Also somewhat similar is H. canadense, but that species usually has the leaves over-topping the inflorescence, the leaf bases are indented like the top of an upside heart, there are no large reflexed appendages between the sepal lobes (sometimes only a small upright tooth), the stem hairs are up to 1 mm long and all of one kind, and the inflorescence branches are mostly hairless, though if sparsely hairy the hairs are all of one length.
Flowering: early May to July
Habitat and ecology: Locally frequent in good quality mesic woods.
Taprooted biennial; stems 3-6 dm, the upper part and infl densely pubescent with short slender hairs 0.3-0.5 mm and conspicuously hirsute with spreading hairs usually 2-3 mm; cauline lvs mostly overtopped by the cymes, orbicular in general outline, 6-15 cm wide at anthesis, truncate or with a broadly V-shaped base, shallowly 5-7-lobed, with obtuse or rounded sinuses; sep separate nearly to the base, densely hirsute, alternating with conspicuous small reflexed appendages; cor lavender or pink-purple, 9-13 mm, the lobes about equaling the tube; stamens and style exsert 1-3 mm; 2n=18. Rich moist woods; s. Ont. to s. Minn., s. to Pa., Tenn., Mo., and e. Kans. May, June. (Decemium a.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Infrequent to common in all parts of the state, although we have no reports for the area near Lake Michigan. It prefers deep leaf mold and is most abundant in beech and sugar maple woods. On rich, wooded slopes of ravines, alluvial plains, and rarely in exposed places on open wooded slopes. Not found on poor black oak slopes. All of the waterleafs do well in cultivation.