D. Don
Description
Tiarella polyphylla is a perennial herb with a wide East Asian and Himalayan distribution, recorded from China, Japan, Korea, Taiwan, Nepal, India, Bhutan and Myanmar, and reliably documented by over 4300 GBIF occurrences. It is a plant of cool, shaded, humid forests, growing in moist humus-rich soil along streamsides, on mossy banks and in the understorey of broadleaved and mixed forest, generally between about 1500 and 3500 m. The photographed populations span Bhutan (Phobjika, 2810 m, May) and eastern and central Nepal (Mewa Khola 2100-2500 m, and Gorkha at Niuli Kharka 2700 m), flowering through the spring months.
The plant grows from a short rhizome and produces a basal rosette of long-petioled leaves; the lamina is cordate-orbicular, shallowly three- to five-lobed, with toothed margins and scattered hairs. The slender, erect flowering stem bears a few reduced cauline leaves and terminates in a narrow, elongate raceme of small flowers. Each flower has five white to greenish, narrow petals and conspicuously exserted stamens, giving the inflorescence a delicate, foamy appearance. The fruit is a distinctive two-valved capsule with markedly unequal valves, splitting to release the small seeds.
Tiarella is a small genus of the Saxifragaceae, and T. polyphylla is the principal Asian representative, the remaining species being North American; this disjunction is a classic example of the eastern Asian-North American floristic link. The plant is shade-tolerant and clonal, often forming loose colonies on forest floors. Though not threatened across its broad range, it depends on intact moist forest and is locally sensitive to logging and disturbance of streamside habitats.
Author: D. Don · Sources: POWO (Kew), GBIF, Flora of China, Flora of Bhutan, Saxifragaceae monograph