Erect shrub to 3 m, green, male or bisexual, densely pubescent with stellate hairs; prickles to 10 mm long, abundant on calyx of bisexual flower, scattered to absent elsewhere.  

Leaves ovate, the upper ones narrowly lanceolate; lamina 5-10 cm long, 2.5-6 cm wide, concolorous or slightly discolorous, entire; petiole 5-20 mm long.  

Male plant: inflorescence condensed, at least 12-flowered; peduncle c. 10 mm long; pedicels c. 5 mm long; calyx 7-10 mm long, the lobes lanceolate, 5-7 mm long; corolla broadly stellate to pentagonal, c. 25 mm diam., purple; anthers c. 7 mm long. Bisexual plant: flowers not known; fruiting pedicel absent or up to c. 5 mm long; fruiting calyx c. 25 mm diam., covering fruit; lobes triangular with linear apices, 20 mm long.  

Berry drying within calyx, the upper portion splitting around circumference in upper portion to form a loose cap. Seeds 2.5 mm long, black.

Martine et al. (2006) have shown that S. vansittartense belongs with the other functionally dioecious species within the Dioicum complex. All of the dioecious members of the Dioicum group of subgen. Leptostemonum exhibit functional dioecy i.e. male flowers are borne on separate plants from what appear to be plants with bisexual or hermaphrodite flowers; while these bisexual flowers do produce pollen, it is inaperturate and does not germinate, making the flowers effectively female (Knapp et al.,1998).

Initial molecular studies by Martine et al. (2006) suggested that the two functionally dioecious species from Kakadu, S. asymmetriphyllum and the newly described S. sejunctum, formed a separate clade and had arisen separately from the other dioecious members of the Dioicum group, S. cunninghamii, S. cataphractum , S. dioicum, S. petraeum, S. carduiforme, S. tudununggae, S. vansittartense and S. leopoldense. This initial DNA analysis involved sequencing of the ITS region of nuclear rDNA.