Greene Rumex hypogaeus (synonym Emex australis), commonly known in English as southern threecornerjack,[2] devil's thorn,[citation needed] or double gee[3] (also doublegee, from the old Afrikaner name dubbeltge-doorn - 'double thorned'), is a herbaceous plant of the Polygonaceae.

It is native in South Africa and is an invasive species in Australia, Texas in the USA, and Pakistan.

It is native to South Africa[1] and has become naturalised in California, Trinidad, Europe, India, Pakistan, Taiwan, Hawaii, and Australia.

[4] Common names in Australia, where it is a weed, include: spiny emex, doublegee, double gee, double-gee, three corner jack, three-cornered jack, goat's head burr, goathead, jackie, prickly jack, cape spinach, devil's face, devil's thorn, bullhead, bull head, and cat's head.

Control programs work best when all plants are killed shortly after emergence, and should continue for several years.