Flora of New Zealand Series

Onehunga weed

Prostrate annual, forming patches up to c. 40 cm diam. Stems sparsely to densely clothed in long hairs, especially toward tips, rooting at nodes. Basal and lower cauline lvs petiolate, sheathing at base, sparsely to moderately hairy, 2-3-pinnatisect, up to 5 × 1.5 cm; primary divisions in 2-5 pairs; ultimate segments narrow-elliptic to subulate, not all in one plane giving a somewhat feathery appearance to the lf. Cauline lvs similar to basal but smaller, mostly 15 × 5-8 mm. Involucral bracts in 1-2 rows, hairy, acute to apiculate, 3-6 mm long. Capitula inconspicuous at flowering, usually scattered along stems, 4-10 mm diam. at fruiting, with (3)-5-20-(27) mature achenes and central florets usually functionally ♂. Achenes glabrous or with short hairs on both surfaces and sometimes on wings, (2.5)-3-6 × 1.3-4.5 mm (including spine), with low central rib on outer face; lateral angles not winged or with narrow to broad thin wings; wings entire or shallowly to deeply 2-lobed, rounded at apex or extended into narrow projections; spine 1.3-2.5 mm long.

N.: throughout, but most common from N. of Lake Taupo; S.: scattered localities in Nelson, Marlborough, Westland, and Canterbury, and collected once from near the Old Man Range (Otago).

Brazil, Paraguay, Uruguay, Argentina, Chile 1883

Lawns, playing fields and golf courses, pastures, and stony waste places.

S. sessilis is very variable in achene morphology (Fig. 18). Cabrera (op. cit.) and Healy (op. cit.) refer plants with lateral achene angles not winged to S. valdiviana Philippi, those with lateral angles winged and deeply lobed to S. pterosperma A. L. Juss, and those with lateral angles winged but not lobed to S. sessilis. However, all 3 forms of achene, and intermediate conditions such as that described as S. neglecta by Cabrera, can often be found in one population, and the forms do not differ in vegetative or floral characters. The achenes within individual plants are ± uniform and a plants progeny retains the same achene form. Plants with differing achene forms can be crossed experimentally and progeny of such crosses have intermediate achenes. Achenes with broad wings are more often hairy than those with narrow or no lateral wings. S. pterosperma and S. valdiviana are therefore treated here as synonyms of S. sessilis. The common name Jo Jo weed is also used for this sp.

S. sessilis is a troublesome weed, particularly when it occurs in lawns and greens, because the sharp achene spines catch in clothing and footwear and may puncture the skin. Germination and establishment of S. sessilis are described by Johnson, C. D. and Lovell, P. H., New Zealand J. Bot. 18 : 487-493 (1980).

Fig. 18. Achenes of Soliva sessilis. © All rights reserved. [Image: 4X49]