Cotula coronopifolia L.
bachelor's button
Ascending to erect, fleshy, glabrous annual or short-lived perennial up to 30 cm tall. Stems terete, branched from base and above, up to 25-(40) cm long, rooting freely from lower nodes. Lvs fleshy, alternate, apetiolate, linear, lanceolate or spathulate, entire, with few irregular large lobes, or shallowly 1-(2)-pinnatisect, usually perfoliate, rarely amplexicaul, (10)-15-80 mm long; lvs above becoming shorter, more triangular, less often divided and more often amplexicaul. Involucral bracts in 2-3 rows, 4-6 mm long. Capitula solitary, bright yellow, (6)-8-10-(13) mm diam.; peduncles scarcely expanded at apex, solid, 2-7 cm long, c. 1 mm diam.; ♀ florets in 1 or < 1 row, pedicellate, with a corolla; ⚥ florets numerous, subsessile, with flattened tubular corolla. Achenes all flattened, hairy on inner surface, glabrous on outer. Achenes of ♀ florets 1.5-2 × 1-1.2 mm; lateral angles with thick, corky, entire, marginal wings. Achenes of ⚥ florets 1.1-1.2 × 0.5-0.6 mm; lateral angles thinly ribbed.
N.; S.: throughout; St.: uncommon; Ch.
Also indigenous to Australia, Africa, and possibly S. America.
Coastal sites, especially lagoons and swamps, also inland in wet sites and waste places.
FL Jan-Dec.
C. coronopifolia is very plastic with plants in poorer sites often producing linear, entire lvs. Allan (1961) suggested that the sp. is most likely introduced and naturalised in N.Z., however, Hooker (1864) noted that it was first collected here by Banks and Solander. The sp. is now a cosmopolitan weed; its dispersal is aided by the corky wings of the outer achenes which float in water. It is also known in N.Z. by the common name buttonweed.
