A study of the development of inflorescence galls on Hypochaeris radicata L. caused by the insect Phanacis hypochoeridis (Kief.)
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Hypochaeris radicata L., commonly called ‘Catsear’, is probably the most widely distributed introduced weed in New Zealand. It is found throughout both islands from sea-level to near the upper limit of vegetation. The wide variety of ecological conditions it occupies includes such varied habitats as coastal sand dunes, all kinds of grasslands from city lawns to alpine snow grass, exotic Cytisus scoparius Link and Lupinus arboreus Sims. and native Leptospermum scoparium Forst. scrub, Pinus and Nothofagus forests, Sphagnum and other bogs, and stream and riverbeds. It is extensively grazed by stock and rabbits, particularly in marginal pastures such as modified tussock grassland and reclaimed coastal dunes. Cockayne (quoted by Healy 1962) rated it as one of the most palatable species and Hilgendorf (1926) considered it the real stock-carrying plant of tussock grasslands. Healy (1962) gives the following description of H. radicata L. "Perennial, with stout tap-root, sometimes multi-crowned; rough hairy with short hairs, rarely ± hairless. Recognized by the thick, obviously hairy leaves with blunt lobes, dull green above and often bluish-green on the undersides, tall, usually branched, leafless flower stalks with scattered bracts, flowerheads large, outer flowers much longer than floral bracts and greenish or violet on the underside, fruiting heads with chaffy scales between the fruits which are all similar, beaked and with inner, long, feathery pappus hairs and outer, short, simple hairs. A variable species, the leaves ranging from nearly entire to deeply lobed, the lobes variously directed. The stalks of this weed commonly show the gall swellings caused by the hymenopterous insect, Aulax hypochoeridis (Kief), this providing an additional diagnostic character." The last part in this description is particularly relevant as it mentions one of the major difficulties encountered during the course of this investigation, and also as it introduces the subject itself.