Erect or ± straggling shrub or woody herb, 0.1-1.3 m, branches strict or ± lax, creeping and rooting at the base; branchlets 2-4-lined when young, eventually terete. Leaves sessile, 0.6-2.5 by 0.3-1.7 cm, narrowly ovate or ovate-triangular to elliptic or broadly ovate or subcircular, apex subacute or rarely acute to rounded, base rounded to cordate, concolorous, plane, spreading or ascending; 4-5(-6) main lateral veins, ± parallel or diverging, much branched, uniting near margin and apex, with marked, usually ± dense, reticulate venation; laminar glands pale, linear towards the base or wholly punctate and striate or punctate only; intramarginal glands pale only or partly or wholly black. Inflorescence 1-flowered, with or without flowering shoots in uppermost axils, or regularly dichasial or intermediate and irregular; pedicels usually exceeding uppermost leaves, 4-20 mm in fruit. Flowers 1.8-2.6 cm ø, plane; buds ovoid to ellipsoid, subacute. Sepals 3-7(-8) by 1-2½(-3½) mm, free, imbricate, ovate to lanceolate or narrowly oblong or sometimes broadly ovate and foliaceous, acute to rounded, entire; laminar glands pale, linear; submarginal glands black or absent. Petals bright yellow, 9-15 by 4v9 mm, obovate, entire, persistent; apiculus short or obsolete; laminar glands pale, linear, sometimes striate distally; marginal glands absent or black, sometimes only in apiculus, rarely few to numerous elsewhere on margin. Stamens not obviously in fascicles (15-)25-40(-50), longest 6-9 mm, c. *A as long as the petals, persistent; anthers bright yellow, gland amber or occasionally black. Ovary (2-)2½-3(-4) mm, narrowly or rarely broadly ovoid; styles 3 (4-5), 2-3 mm, ¾ as long to as long as the ovary, divergent; stigmas narrowly to broadly capitate; placentas 3(-4-5), parietal. Capsule (5-)7-9(-10) by 3-4½ mm, narrowly ovoid or rarely broadly ovoid to ellipsoid, longitudinally vittate. Seeds yellow-brown to dark brown, 0.7-0.8 mm, cylindric or subcylindric, scarcely carinate, densely linear-foveolate to linear-scalariform.
Asia-Tropical: widespread in all mountainous regions: present
Malesia: New Guinea (widespread in all mountainous regions). .
H. papuanum is a very variable species in which the extreme forms, although quite distinct in appearance, are linked by intermediates with varying combinations of characters, so that the morphological trends are not coordinated. These trends are:
- Leaves narrowly ovate and ± crowded with laminar glands mostly linear (in E., W. and S. Highlands mainly) to broadly ovate or sub-circular, not crowded, with laminar glands all punctiform (constant in W. New Guinea and E. Papua, Northern and Milne Bay Districts).
- Leaves, sepals, petals and anthers without black glands (mainly eastern) to with black glands, forming a continuous intramarginal row in the leaves (constant in W. New Guinea) and sepals and a continuous marginal row in the petals (rare).
- Inflorescence 1-flowered (mainly eastern) to regularly dichasial (mainly western).
- Styles and placentae 3 with ovary and capsule narrowly ovoid (mainly eastern) to styles and placentae 4-5 with ovary and capsule ± broadly ovoid (mainly western). According to A.C. SMITH, l.c, H. habbemense may have up to 6 styles but only up to 5 placentae. A reexamination of the syntype material has failed to reveal an ovary with 6 styles and 5 placentae, a combination of characters that is probably teratological in origin.
- Habit dense with ± ascending branches (widespread) to lax with ± spreading branches (Madang and Morobe Districts).