Commersonia J.R.Forst. & G.Forst.

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

Distribution

A genus of about 12 species, all occurring in Australia but the range of the genus extending to South-East Asia and the Pacific; two species are found in New Guinea: the common Commersonia bartramia (L.) Merr., and montane C. novoguineensis (Gilli) Guymer.

Morphology General Habit

Trees and shrubs to 25 m tall

Morphology General Indumentum

Indumentum usually copious, stellate

Morphology Leaves

Leaves alternate, simple, sometimes irregularly lobed, base cordate, often unequal, margin serrate to dentate

Morphology Reproductive morphology Inflorescences

Inflorescences axillary or leaf-opposed, rarely terminal, axis branching dichotomously, the fundamental unit a dichasium, usually many-flowered

Morphology Reproductive morphology Flowers

Flowers 5-merous, bisexual, actinomorphic; sepals fused at the base; petals ligulate, less than ½ the width of the sepals, becoming wider and concave at the base; stamens 5, opposite the concave base of the petals, alternating with the 3-lobed staminodes; ovary 5-locular, at first concealed by staminodes, revealed as they recurve, 2–6 ovules per locule, style branched

Morphology Reproductive morphology Fruits

Fruit a loculicidal capsule, 5-valved, exocarp bristly echinate

Morphology Reproductive morphology Seeds

Seeds 1–2 per locule, glabrous.

Ecology

Commersomia bartramia is found in a variety of habitats at comparatively lower elevations, usually secondary, regrowth and disturbed habitats, but also rain forest and open grassland; from sea level to c. 400 m. Commersonia novoguieneensis is found in montane habitats including lower montane forest, secondary growth and garden edges, from 1500–2800 m.

Recognition

Commersonia can be distinguished from other Byttnerioideae genera in New Guinea by the many-flowered, dichotomously branching inflorescence, the ligulate petals and echinate fruit, which, unlike that of Seringia, is not lobed. The undersurface of the leaves of C. bartramia are distinctly greyish both in the field and in the herbarium.