Zygogynum Baill.

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. 50 species, from western Malesia through to New Caledonia and Australia; 22 species recorded from New Guinea. The genus Zygogynum was until relatively recently, considered endemic to New Caledonia with the genus Bubbia in Malesia, New Guinea and Australia, but considered separate due to having free carpels. However, Vink (1985), examined material of Bubbia, Zygogynum and the genus Exospermum and found intermediates between free and fused carpels and place all three genera in Zygogynum. There is still some debate if Zygogynum and Bubbia should be kept distinct and the recent Flora of Australia treatment kept them seperate; Zygogynum is used here following Vink (1993).

Morphology General Habit

Shrubs or trees to 20 m in New Guinea; branching sympodially after flowering

Morphology Leaves

Leaves alternate

Morphology Reproductive morphology Inflorescences

Inflorescences terminal, in compound dichasia to triads or solitary, 1–23-flowered

Morphology Reproductive morphology Flowers

Flowers bisexual; calyx calyptrate, soon rupturing, persistent; petals 4–14, free, 1–3-seriate, white, cream or yellow; stamens 8–32, inflated, obovoid to slightly flattened (or laterally widened); carpels 1–8, free, stigma sessile, ovules 6–22 per carpel, in 1 or 2 rows

Morphology Reproductive morphology Fruits

Fruit apocarpous, monocarps berry-like. Seeds 3–12 per monocarp, obovoid or oblong-ovoid, slightly falcate, black, smooth or slightly pusticulate.

Ecology

Species of Zygogynum have been found from primary or disturbed habitats including lowland rain forest and hillside or ridgetop forests to subalpine shrubberies; from sea level to c. 3200 m elevation. Zygognyum differs from Tasmannia in several characters but most conspicuously in the inflorescence position and calyx. Members of Zygogynum have a terminal inflorescence and sympodial branching from a vegetative bud in the axil of a cataphyll subtending the inflorescence axis, and the calyx is thicker, rarely calyptrate and enclosing the bud and persistent below torus with the individual fruits.