Erect, rhizomatous perennial shrub, 0.3-0.9 m tall. Juvenile stage unknown. Stems brown, glabrous to sparsely pubescent, the stellae 0.2-0.3 mm in diameter, the stalks 0-0.1 mm long, the lateral rays 4-8, porrect, the midpoints 0.5-1.5 times as long as lateral rays, eglandular; finger hairs absent; very short, gland-tipped hairs sparse to dense; prickles present or absent, straight, acicular, 0.5-5 mm long, 7-10 times longer than wide, 0-6 per dm on adult branches.
Sympodial units plurifoliate, not geminate.
Leaves simple, the blades 5-9.5 x 1.1-1.5 cm, 4.7-7 times as long as wide, narrowly lanceolate to lanceolate, chartaceous, green and glabrous to sparsely stellate-pubescent adaxially, the hairs confined to midrib; finger hairs absent; very short, gland-tipped hairs present throughout, 0.1-0.5 mm apart; prickles present on midvein only, 0-4, straight, acicular, 3-7 mm long; green and glabrous abaxially; finger hairs absent; very short, gland-tipped hairs absent; prickles absent or present on midvein only, 0-3, straight, acicular; base cuneate, the oblique part 0-2.5 mm long; margin entire; apex acute; petioles 0.9-2.1 cm long, 11-23% length of lamina, glabrous to sparsely pubescent, prickles present or absent.
Inflorescence 0.5-2 cm, leaf-opposed, unbranched, pseudo-racemose, with 3-8 flowers, with all flowers perfect, the axes glabrous to moderately glandular-puberulent, unarmed; peduncle 0-2 cm; rachis 0.1-0.5 cm; pedicels 9-24 mm long in flower, 0.4-0.7 mm thick at midpoint, the same thickness throughout or markedly thicker distally,18-24 mm long in fruit, 0.6-0.8 mm thick at mid-point, spaced 1-10 mm apart, articulated at the base.
Flowers all perfect, 4- or 5-merous. Calyx 4-7.5 mm, the tube 1.5-2.5 mm long, the lobes 2-6 mm long, attenuate, glabrous to sparsely stellate-pubescent, the hairs white, 0.15-0.3 mm across, sessile, the lateral rays 4-8, the midpoints 0-1 times as long as lateral rays, eglandular; finger hairs absent; very short, gland-tipped hairs present; prickles absent; fruiting calyx not accrescent, less than half length of mature fruit, unarmed. Corolla ca. 1 cm in diameter, 7-11 mm long, stellate to rotate-stellate, chartaceous, purple, the tube 2-3 mm, the lobes 3-8 x 1.5-2 mm, narrowly triangular, abaxially glabrous at base of lobes, pubescent toward tips with unbranched and stellate hairs, glabrous adaxially. Stamens with filaments 0.5-1 mm; anthers 3-5 x 1-1.5 mm at base, narrowly ovate, loosely connivent, yellow, the pores minute and directed distally. Ovary glabrous or with very short, gland-tipped hairs only; style 5.5-7 x 0.5-1 mm, cylindrical, glabrous; stigma capitate or bilobed.
Fruits 1-4 per inflorescence, 0.8-1.1 cm in diameter, 1-locular (septum absent or incomplete), globose, red, glabrous, few- (less than 20-) seeded, the exocarp 0.4-0.5 mm thick, the mesocarp juicy, succulent, the placenta not apparent.
Seeds 3-3.7 x 2-2.5 mm, pale yellow, flattened, the surface rugose.
Solanum lythrocarpum is endemic to Queensland. It is known from two small areas near the towns of Monto and Mundubbera. It grows on lateritised plateaux in ironbark-Acacia blakei forest with a dense shrubby understorey including some rainforest species. Associated species include Croton insularis, Phebalium nottii, Bertya opponens and Philotheca ciliata.