2. Tiarella trifoliata Linnaeus, Sp. Pl. 1: 406. 1753.
Three-leaf foamflower Three-leaf foamflower
Flowering stems 10-70 cm. Leaves simple or 3-foliolate; cauline leaves 1-4, simple or 3-foliolate; petiole 0.2-20 cm; blade 2-10 × 3-15 cm. Inflorescences narrow panicles, 15-70-flowered, 10-70 × 1-5 cm. Pedicels subtended by finely dissected bracts, 0.1-1.2 cm, glandular-stipitate. Flowers: hypanthium campanulate, 2-3 mm, glandular-stipitate; perianth somewhat bilaterally symmetric; sepals spreading at anthesis, reflexed in fruit, 1-1.5 × 0.5-0.8 mm; petals caducous, spreading, linear or subulate, unlobed, 2-3 × 0.5 mm, base clawed, apex attenuate; stamens unequal, 3-4 mm and 1.8-2.5 mm; anthers oblong, 0.4-0.5 mm. Capsules 0.6-0.9 cm. Seeds 2-6, ovoid, 1.2-1.5 × 0.6-0.9 mm.
Varieties 3 (3 in the flora): w North America.
Varieties of Tiarella trifoliata have overlapping ranges and differ from each other in leaf form and marginal dissection. Their floral features are stable throughout. They were previously suspected of hybridizing when sympatric. They are differentiated along elevational gradients and often remain distinct in sympatric populations.