Family: Polygonaceae
Rumex spinosus (devil’s-thorn, lesser-jack) is an annual herb native to Macaronesia, Mediterranean to Sahara & Sahel, and the Arabian Peninsula to Iran. The leaves are bitter, but they are still edible. It is reported to be naturalized in Australia as well as Oʻahu, Molokai, Maui, and Hawaiʻi Island. This species contains spines, creates numerous seeds that stick to animals and vehicles, is an agricultural weed and creates dense stands where it grows. For these reasons it is a high risk plant.
High Risk Traits:
- Elevation range exceeds 1000 m, demonstrating environmental versatility
- Grows in tropical climates
- Naturalized on Oahu, Molokai, Maui, and Hawaii (Hawaiian Islands), Australia, and elsewhere
- A disturbance-adapted weed that impacts agriculture and potentially the natural environment
- Other Emex species are invasive
- Spine-tipped achenes
- Allelopathic
- Tolerates many soil types
- Capable of forming dense cover in disturbed habitats
- Reproduces by seeds
- Hybridizes with Emex australis
- Self-compatible
- Reaches maturity in one growing season (annual)
- Seeds dispersed by sticking to animals and vehicles, by wind, water and as a seed contaminant
- Prolific seed production
- Might form a persistent seed bank (based on traits of related taxon)
Low Risk Traits:
- Thrives in open, disturbed habitats (may be shade intolerant)
- Not reported to spread vegetatively
- Herbicides and mechanical methods have provided effective control
- Biocontrol agents have been introduced into the Hawaiian Islands
