Hydrangea Gronov. ex L.

Timothy M. A. Utteridge and Laura V. S. Jennings (2022). Trees of New Guinea. Kew Publishing. Royal Botanic Gardens, Kew

Distribution

A genus of c. 75 species, distributed in temperate parts of the Americas (not in Amazonia) and east Asia, through Malesia reaching New Guinea and the Solomon Islands (not recorded from Africa or Madagascar). A single species occurs in New Guinea: Hydrangea febrifuga (Lour.) Y.De Smet & Granados, previously placed in the genus Dichroa Lour. but moved into an enlarged Hydrangea by De Smet et al. (2015).

Morphology General Habit

Shrubs or sometimes small trees to 6 m (in New Guinea)

Morphology Leaves

Leaves opposite, rarely alternate, margins serrate. Inflorescence terminal, a cymose panicle

Morphology Reproductive morphology Flowers

Flowers bisexual; calyx tube adnate to ovary, obconical, calyx lobes usually 5; petals usually 5(or 6), blue or pinkish; stamens 4–10(–20), filaments filiform or subulate, anthers ellipsoid to ovoid, 2-loculed; ovary semi-inferior to completely inferior, 3–5-loculed, placentation parietal, ovules numerous; styles 2–6, free or connate only at base, divergent, stigma oblong to subglobose

Morphology Reproductive morphology Fruits

Fruit a berry, slightly dry. Seeds numerous, ovoid, minute.

Ecology

In New Guinea, Hydrangea febrifuga occurs in primary rain forest and montane forest, from 100–2000 m.

Recognition

The genus can be recognised by the shrubby habit rarely becoming a small tree, the opposite leaves with serrate margins, the terminal inflorescences with blue or pink flowers and the inferior ovary. It can be confused with Chloranthaceae, but that family does not have inferior ovaries or coloured flowers.