Variation in achene morphology and its implications for taxonomy inSolivasubgenusSoliva(Anthemideae, Asteraceae)

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Abstract
Species of the South American genus Soliva are troublesome weeds because they invade turf areas and have spinous achenes. Soliva is now widely naturalised in New Zealand and the plants are known here as Onehunga weed. The four species usually accepted for subgenus Soliva, three of which are recorded for New Zealand, are distinguished by characters of the achenes, but are identical in vegetative and floral characters. Examination of herbarium and field material of naturalised New Zealand plants has shown that these achene characters are continuously variable. Many forms previously referred to separate species, as well as intermediates between them, co-occur within populations. Individuals are self-pollinating and produce seedlings with the same achene form. Experimental crosses between plants with the most distinctive achene forms produced fully fertile progeny with achenes intermediate between those of the pollen and seed parents. It is concluded that subgenus Soliva consists of a series of inbreeding forms best regarded as a single species, S. sessilis, which is very variable in achene morphology. It is also suggested that there may be fewer good species in subgenus Gymnostyles than are usually accepted, and that the elevation of subgenus Gymnostyles to generic rank, as proposed by some authors, may not be warranted.

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