A native of India, Burma and possibly Thailand, Laos and Cambodia, cha-om was first recorded in Queensland in 2001 near Innisfail. To date, it has mainly been recorded in gardens.

However, if it were to escape from cultivation, it can form thorny thickets, resulting in serious impacts to pastures and grazing areas and potentially beef production. It may invade disturbed habitats, particularly moist areas on the margins of rainforest, and can invade natural ecosystems. For these reasons, the introduction, keeping, releasing and supplying of this species is prohibited.

Cha-om is a fast-growing shrub or scrambling vine which can reach a height of 5 m (Fig. 1).

Its leaves are finely bipinnate (Fig. 2) with small leaflets and scattered prickles along its branchlets and stem. The petiole (leaf stalk) has a large gland at its base, visible to the naked eye (Fig. 3). The leaves, stems and flowers have a very strong, unpleasant smell. Flowers are cream to yellow, and the seed pods are flattened.

Cha-om looks similar to and is a close relative of two native species, Senegalia pennata subsp. kerrii (listed as ‘vulnerable’) and Senegalia albizioides (‘near threatened’). Senegalia pennata subsp. kerrii is a climbing vine with hooked prickles known only from Cape York, north of Bamaga. It lacks the pungent odour of cha-om. Senegalia albizioides is also a climbing vine that occurs from Innisfail north to Cape York. It has broader leaflets and again lacks the odour of cha-om.

Cha-om can be confused with other non-native members of the Mimosaceae family, such as Leucaena (Leucaena leucocephala) and the common sensitive plant (Mimosa pudica). Leucaena is a tall shrub that lacks prickles and a strong odour. The common sensitive plant is a spreading herb to 45 cm height with pink flowers and leaves that close up when touched. Poinciana (Delonix regia, Caesalpiniaceae) also has similar looking leaves but grows into a large tree with red flowers, no thorns and is without a distinctive odour.

If you think you have seen (or smelled) cha-om growing in your region, please contact the Queensland Herbarium on (07) 3199 7671, email a photograph to the Queensland.Herbarium@qld.gov.au or contact Biosecurity Queensland on 13 25 23.