D. Don
Description
Hydrangea heteromalla is a deciduous shrub or small tree of the Himalaya and central China, with GBIF returning over 1600 occurrences spanning its native range in China, Nepal, India, Bhutan and Myanmar as well as numerous cultivated and naturalised records from Europe and North America. In the wild it grows in cool temperate forest, on open slopes, forest margins, ravines and shrubberies, typically between about 1500 and 3500 m. The plant photographed near Lachen in northern Sikkim at about 2760 m, flowering in June, occupies the moist temperate montane belt where the species is a frequent understorey and edge shrub.
The plant has stout, spreading branches with peeling bark and opposite leaves that are ovate to elliptic, acuminate, finely serrate, and characteristically discolorous, dark green above and densely pale-tomentose to whitish beneath, the indumentum giving the epithet heteromalla. The inflorescence is a broad, flat-topped to slightly domed corymb bearing many small fertile flowers surrounded at the margin by larger, showy, sterile ray-florets with four enlarged white sepaloid segments. The fertile flowers are small, white, with five petals and numerous stamens. The fruit is a small ribbed capsule opening at the apex to release numerous tiny seeds.
Hydrangea heteromalla is a variable and widespread species, the subject of much horticultural selection and the source of cultivated forms grown for their lacecap inflorescences, which explains its scattered records across temperate gardens worldwide. Within Hydrangea section Hydrangea it represents the principal Himalayan-Chinese montane lineage. Ecologically the marginal sterile florets serve to attract pollinators to the inconspicuous fertile flowers. The species is common and not threatened, and its wide ecological amplitude and ornamental value have ensured both its persistence in the wild and its global cultivation.
Author: D. Don · Sources: POWO (Kew), GBIF, Flora of China, Flora of Bhutan, McClintock "A Monograph of the Genus Hydrangea", Annotated Checklist of the Flowering Plants of Nepal