Appearance

Spiny Emex, Emex spinosa is an autumn-winter germinating annual with branching, round, ribbed, and sometimes reddish stems. Stems may be decumbent to erect and radiate out from the crown. It is native to the Mediterranean andd Africa but is now found around the world.

Foliage

Leaves are triangular with a truncate to slightly cordate base. Margins are smooth to wavy. Basal leaves are largest, (up to about 6 in. long), and become smaller as they move up the stem (about 1 in. long). There is a brown membranous ochreae at the base of the petioles. Basal leaves often have a petiole that is longer than the leaf.

Flowers

The small green flowers have predominantly separate sexes but are self-compatible. The spiny female flowers are sessile and form in axillary clusters in the axils of the leaves. The male flowers, together with the occasional perfect flower, form in short axillary racemes,

Fruit

Fruits are achenes which contains a single, trigonous seed. Aerial achenes have very sharp spines and are formed at the nodes of the above-ground stem. Achenes turn from green to brown as they mature.

Ecological Threat

E. spinosa has an erect growth habit and a seed size similar to grain which makes it a potential problem to the grain-growing industry which has to limit the rate of contamination be seed from weedy species. The spiny fruits can cause injury to livestock and wildlife. Its drought tolerance, rapid growth rate, and prolific seed production allow it to compete successfully in disturbed and undisturbed sites. In natural areas, the spiny seed pods can stick to people and animals, spreading them along trails and then into more undisturbed areas. It has already become a serious problem in Hawaii.

Citations

Winston, R.L., Andreas, J.E., Milan, J., DesCamp, W., Randell, C.B., and M. Schwarzlander. 2014. New Invaders of the Southwest. United States Department of Agriculture, Forest Health Technology Enterprise Team. FHTET-2014-12. Retrieved from https://bugwoodcloud.org/resource/files/14767.pdf

Rawlins, K.A., R.L. Winston, C.T. Bargeron, D.J. Moorhead, and R. Carroll. 2018. New Invaders of the Northeast and Northcentral United States. USDA Forest Service, Forest Health Assessment and Applied Sciences Team, Morgantown, West Virginia. FHTET-2017-04. Retrieved from https://bugwoodcloud.org/resource/pdf/FHTET-2017-04_New%20Invaders_NE.pdf
 

Selected Images

Maps

Invasive Listing Sources

• California Invasive Plant Council
• Federal Noxious Weeds
• Florida Noxious Weeds
• Hawaii Noxious Weeds
• Massachusetts Noxious Weeds
• Massachusetts Prohibited Plant List
• New Invaders of the Northeast and Northcentral
• New Invaders of the Southeast
• New Invaders of the Southwest
• South Carolina Plant Pest List
• USDA APHIS Regulated Pest List