Xanthium strumarium clotbur; cocklebur Asteraceae XAST*; Bx, pb; NY, hb; Q, a, i, j, rb; K, m; R, ar, c, cs, fk, gr, hs, lc, v;

 

Xanthium strumarium.T. Beth Kinsey.fireflyforest.net

Xanthium strumarium.T. Beth Kinsey.fireflyforest.net. (Accessed 5/2014).

Annual C3 herb (Ludwig et al 2010)from a taproot, stem 20 cm to 2 m tall, erect, coarse, glandular-hairy, often sticky and branching, purple-spotted. 

Leaves, alternate above, lowest pair sometimes opposite, broadly oval, margin coarsely toothed or lobed. 

Flowers green, sexes separate, male flowers small, in short, dense, bracteate spikes, pollen highly allergenic (similar to ragweed, Ambrosia), wind pollinated, but mostly self-pollinated; female burs 1-2 cm long, oval-cylindrical with hooked spines, 2 larger in-curved spines at apex, bur 2-chambered each with 1 seed; blooms Aug.-Oct., will not flower if photoperiod is more than 14 hrs. (Weaver and Lechowicz 1983). 

Xanthium strumarium.Steven Baskauf.New England Wild Flower Society.gobotany.newenglandwild.org

Xanthium strumarium.fruit.Steven Baskauf.New England Wild Flower Society.gobotany.newenglandwild.org ( Accessed 5/2014).

Fruit, dry, to 0.2 cm, flattened achene, toxic, cotyledons contain carboxyatractyloside, (older seedling and plants rough but not toxic); fruits Oct.-Nov. Seeds dispersed into winter by burs clinging to fur or clothing, also able to float for up to 30 days. Seeds buried in soil loose viability within a 2-3 years. 

Wetland status: FAC. 

Frequency in NYC: Occasional. 

Origin: Native to the New World. 

Habitat: Open, disturbed areas especially beaches, shores, fill. An agricultural weed. Prefers sandy soil, pH 5.2-8.0, tolerates flooding and salt. Intolerant of shade. 

Notes: Adaptation to water dispersal and flood tolerance may indicate Cocklebur originally occupied ephemeral stream bank and open flood plain habitats (Marks 1983). Seeds of Cocklebur are attacked by the larvae of a moth, Phaneta imbridana, and of a trypetid fly, Euaresta aequalis. Both insects tend to affect smaller burs rather than larger ones Plants are also attacked by the rust Puccinia xanthii, an obligate parasite of Cocklebur and of Ambrosia spp. The fungus causes damage to leaves, leaf drop, and splitting of petioles and stems. Cocklebur is host to a number of other fungi including Septoria xanthiiCercospora xanthicola, Mycosphaerella xanthicola and other fungi that specialize on Xanthium spp. The nematode Aphelenchoides ritzema-bosi has also been found on Cocklebur (Weaver and Lechowicz 1983).