February 2015. Recently, some cattle died on a sugarcane plantation in Papua New Guinea. We suspect this weed. It grows near disturbed areas such as roads, cattle yards, etc. We would appreciate an ID and comments whether this plant is toxic to cattle.

The weed was identified by members as Tribulus terrestris, puncture vine in the family Zygophyllaceae a very common roadside weed (in India). It has thorny fruits. It is possibly native to Eastern Polynesia and other island in the Central Pacific and maybe introduced into tropical America, but is found and has become naturalized on some Pacific Island, such as Kiritimati Atoll in Kiribati.

The weed was said to be common in the Markham and Ramu Valley, PNG. The related T. terrestis is reported to be toxic to livestock so it could also contain such poisonous chemicals. Two biocontrol agents (Microlarinus lareynii and M. lapyriformis) were released in 1966 and 1967, respectively. Only M. lapriformis has established and gives some control from time to time.

Tribulus cistoides has been reported from Central Province (around Port Moresby), since at least 1935 (by E.H. Carr, who reported a vernacular name implying it may have been there for some time).

The very similar (possibly the same?) Tribulus terrestris was collected in Port Moresby as early as 1893 (by horticulturalist Ebenezer Cowley on his sugarcane collecting visit from Kamerunga (Cairns) for the Queensland Agriculture Department.

See the invaluable Plants of Papua New Guinea Database http://www.pngplants.org/PNGdatabase.

E.E. Henty and G.H.Pritchard Weeds of New Guinea and their control ( Botany Bulletin No. 7. Lae, Division of Botany, Department of Forests) describe Tribulus cistoides as dangerous to livestock (p. 162).