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Emex spinosa (L.) Campderá
Common names: devil’s thorn, spiny emex, lesser jack
Fruit an achene enclosed in persistent hardened perianth, 4-8 mm long, 2.4-5 mm wide and thick (not including spines). Three sided, each side with 6-10 depressions in upper portion, arranged in 2 columns, and 2 depressions in lower portion; all the lower depressions together form a tapered base. Toward the apex, each edge (of outer segments) forms a rigid recurved spine. Three inner segments form an erect, connivent apex taller than spines. Cross section triangular to nearly round. Surface dull, light to dark straw colored or reddish-brown; dusty appearance, rough. Scar variable. Embryo peripheral, J-shaped, cotyledons longer than radicle; endosperm readily visible.
The spiny fruits of Emex spinosa and Emex australis distinguish this small genus of only two species from Rumex, Fagopyrum and Polygonum.
Emex australis Steinh.
Mediterranean countries, Australia, Kenya, and Mauritius; South America: Argentina, Brazil, Paraguay, Uruguay; United States.
Native to the Mediterranean.
Sandy shores, disturbed ground, perennial crops, grasslands.
Emex spinosa is an erect, annual herb, up to 40 cm tall. E. spinosa has been found growing with E. australis in Australia. It has the potential to become a serious weed (like E. australis) by reducing the yield of cereal crops, and by causing injury to livestock with its spiny fruits.