Small to moderate, solitary or clustered, unarmed, pleonanthic, monoecious palms. Stems erect, usually slender, smooth, often grey, obscurely or conspicuously ringed with leaf scars. Leaves pinnate, rather short, vertical to ± horizontal, relatively few in the crown; sheath elongate, forming a prominent crownshaft, bearing tattered, peltate, or tufted scales and tomentum, the sheath apex with or without a triangular or ligulate, sometimes divided appendage opposite or to one side of the petiole; petiole short or elongate, channelled adaxially, usually rounded abaxially, tomentose or with scales; rachis longer than the petiole, adaxially ridged, abaxially rounded, variously scaly; leaflets regularly or irregularly arranged, or clustered, single-fold, wedge-shaped, linear or wider medianly, apices obliquely or concavely praemorse, or praemorse and notched, the margins extending beyond the midrib, midrib always prominent, marginal ribs thickened, usually glabrous adaxially, the large or small distal leaflets linear to broadly wedge-shaped, ramenta present or absent along abaxial ribs, transverse veinlets evident (?always). Inflorescences infrafoliar, branched usually to 2, 3, or 4(–6) orders, protandrous; peduncle usually short but elongate in Ptychosperma tagulense, angled, glabrous, or with scales and tomentum throughout; prophyll tubular, dorsiventrally flattened, keeled laterally, attached at the base of the peduncle, splitting apically, then abaxially, early caducous; peduncular bract tubular, similar to, attached close to, and enclosed by the prophyll, often with a hard short or tapering beak, splitting abaxially, early caducous, an incomplete peduncular bract usually present; rachis longer than the peduncle except where peduncle elongate; rachis bracts triangular to ligulate, or short, stubby, in horizontal furrows, spirally arranged; rachillae elongate, often fleshy, bearing spirally arranged bracts similar to the rachis bracts, subtending triads basally and paired to solitary staminate flowers distally, from as few as 4 to more than 100 clusters per rachilla depending on the species; floral bracteoles short, rounded. Staminate flowers bullet-shaped to ovoid, lateral to the pistillate in triads; sepals 3, distinct, broadly imbricate, sometimes gibbous, margins fringed, tips shortly pointed; petals 3, distinct, ovate, rather thick, fibrous, valvate, grooved adaxially, 3–4 times as long as the sepals; stamens 9–over 100, arranged in alternating antesepalous whorls of 3 and antepetalous whorls of several (Uhl and Moore 1980), filaments short, awl-shaped, not inflexed, anthers linear-lanceolate, strongly, often unevenly sagittate basally, bifid apically, dorsifixed near the middle, versatile, latrorse, connective elongate, tannniferous; pistillode bottle-shaped with a long neck, irregularly cleft apically, or short, conic-ovoid, trifid or tripapillate apically. Pollen ellipsoidal asymmetric, occasionally pyriform or lozenge-shaped; aperture a distal sulcus; ectexine tectate, perforate, or perforate-rugulate, aperture margin similar or slightly finer; infratectum columellate; longest axis 32–62 µm; post-meiotic tetrads tetrahedral, sometimes tetragonal or, rarely, rhomboidal [14/28]. Pistillate flowers shorter than the staminate, conic-ovoid; sepals 3, distinct, broadly imbricate, sometimes gibbous, marginally fringed; petals 3, distinct, broadly imbricate, tips valvate, thick, pointed, opening slightly but not reflexed at anthesis; staminodes tooth-like, linear or united, then broad, toothed or ribbed, and scale-like; gynoecium conic-ovoid, unilocular, rarely bi- or trilocular, stigmas 3, short, reflexed at anthesis, ovule hemianatropous, 5-angled, pendulous, funicle long, bearing a short aril. Fruit globose to ellipsoidal, red, orange or purple-black at maturity, stigmatic remains apical, forming a beak, perianth persistent; epicarp granular due to short or long, oblique, fibrous bundles and interspersed brachysclereids, mesocarp fleshy, mucilaginous or tanniniferous, sometimes with irritant needle crystals, endocarp fibrous with vascular bundles with large fibrous sheaths at several levels and extending into the inner mesocarp or united in a single layer (P. salomonense), usually adherent to the seed. Seed longitudinally 5-grooved or angled, rarely 3-grooved or rounded in cross-section, hilum lateral, raphe branches few, sparsely branched, endosperm homogeneous or ruminate; embryo basal. Germination adjacent-ligular; eophyll bifid. Cytology: 2n = 32.
Each of the four subgenera and the two sections of subgenus Actinophloeus has a distinct range and habitat. The centre of diversity of subgenus Ptychosperma and the two sections of subgenus Actinophloeus is the mountainous south-eastern tip of New Guinea, where each of the groups has a number of endemic taxa. Some species inhabit coastal or swampy lowland forests, others the better-drained edges of these areas or foothills. Ptychosperma vestitum is exceptional in occurring in fresh-water swamps. Pollination in P. macarthurii is mostly by bees of the genus Nomia (Halictidae), which are attracted to flowers of both sexes by nectar (Essig 1973).