three-cornered jack

plural three-cornered jacks

1. AustraliaA weed of species Emex australis.

   Many chemicals are being tested at Mildura in an attempt to control some of the more difficult weeds such as hard-head thistle (Centaurea repens) and three cornered jack/Devils thorn (Emex australis).

   1963, Victorian Department of Agriculture, The Journal of Agriculture, volume 61, page 504

   3 more examples

   1901, South Australian Department of Agriculture, South Australian Department of Industry, Journal of Agriculture and Industry of South Australia, Volume 4, page 385, The “Three-cornered jack/Devils thorn” (Emex australis) is believed to be poisonous to them, as many dead locusts are found near to each plant.

   There is also the three-cornered jack, which runs along the ground and has somewhat fleshy green leaves. The seed vessels have four spikes like those of the iron caltrops which used to be laid down to cripple the horses of charging cavalry.

   1969, Percival Vincent Wake, Opal men, page 23

   For example, three-cornered jack or double-gee (Emex australis) infests grain crops and reduces grain yield, and the spiny fruits cause severe contamination of produce such as vine fruits, peas and lupins in storage.

   2002, T. R. New, Insects and Pest Management in Australian Agriculture, page 41

   Synonyms: devils thorns, doublegee, spiny emex, bindi, bindi-eye, bindii, cathead, cat's head, doublegee

2. A seed vessel of this plant, which has three symmetrically arranged thorns and a pointed head.