13. Tiarella Linnaeus, Sp. Pl. 1: 405. 1753; Gen. Pl. ed. 5, 190. 1754.
Foamflower, tiarelle [Latin tiara, turban, and -ella, diminutive, alluding to capsule shape]
Herbs (often evergreen), rhizomatous, sometimes stoloniferous; caudex creeping, scaly. Flowering stems erect, usually leafless, rarely with 1-2 leafy bracts, 10-70 cm, short to long glandular-stipitate. Leaves in basal rosette and, sometimes, cauline, simple or 3-foliolate; stipules present; petiole short to long stipitate-glandular (hairs usually denser distally, gland-tipped); blade cordate or broadly ovate, lobed, base cordate, margins crenate to dentate, apex acute, abaxial surface stipitate-glandular along veins, adaxial surface stipitate-glandular, sometimes appressed, hairs uniformly scattered; venation palmate. Inflorescences racemes (sometimes with paniculate branches at base) or panicles, terminal from axillary buds in rosette, 15-70-flowered, bracteate. Flowers radially symmetric or somewhat bilaterally symmetric; hypanthium barely adnate to ovary proximally, 0.2-0.9 mm free from ovary, white or pinkish, (campanulate); sepals 5, whitish or pinkish, (ovate to lanceolate, apex acute or obtuse, glandular-stipitate abaxially, glabrous adaxially); petals 5, white or pinkish to purplish; nectary disc absent or inconspicuous; stamens 10; filaments linear; ovary superior, 1-locular, carpels connate, unequal; placentation parietal; styles 2, (tapering); stigmas 2. Capsules 2-winged (beaked), unequally valvate, abaxial carpel 1.5-2 times longer than adaxial carpel, (papery, each wing 5-10-veined). Seeds black, shiny, ellipsoid or ovoid, (base truncate), puncticulate; (funicular appendage absent). x = 7.
Species 3 (2 in the flora): North America, Asia.
Intergeneric hybrids between Tiarella cordifolia and species of Heuchera and Mitella have been documented. Tiarella is placed within the Heuchera group of the Saxifragaceae. Based on cpDNA and other cytological traits, this is one of the best-defined groups of the Saxifragaceae. Chloroplast DNA restriction site data for the Heuchera group suggest the group as being paraphyletic. Tiarella cordifolia is known from eastern North America and T. trifoliata is known from western North America. Tiarella polyphylla D. Don occurs in Asia in the Himalayas through western and central China to Japan and Taiwan. Tiarella is used as a diuretic as well as for suppression of urine production and in treating kidney stones.
SELECTED REFERENCE Lakela, O. 1937. A monograph of the genus Tiarella L. in North America. Amer. J. Bot. 24: 344-351.