Emex australis

Rumex hypogaeus (synonym Emex australis), commonly known in English as southern threecornerjack, devil's thorn, or double gee (also doublegee, from the old Afrikaner name dubbeltge-doorn - 'double thorned'), is a herbaceous plant of the Polygonaceae. It occurs indigenously in South Africa and is also an invasive species in Australia & Texas in the USA.