Grecian Thistle in North Canterbury

New Zealand Journal of Agriculture, Volume 72, Issue 1, 15 January 1946, Page 3

Grecian Thistle in North Canterbury

GRECIAN thistle, a recent addition to the weeds of New Zealand, seems, from local reports, , to have been established in parts of North Canterbury for at least 20 years. This article by A. J. Healy, Botany Division, Plant Research Bureau, Department of Scientific and Industrial Research, records the writer’s botanical observations on the plant and discusses aspects of habitat, dispersal, control, and economic importance that are s of interest to the man bn the land. GRECIAN thistle, a recent ad- , dition to the weed flora of New Zealand, is a native of Asia Minor and Greece, belonging to a genus which is distributed in the Mediterranean region. The genus Chamaepeuce is closely related to Cirsium, which includes the Scotch thistle (.Cirsium lanceolatum), and Carduus, which includes the winged thistle (Carduus tenuiflorus), ' all species widely dispersed in New Zealand. First Appearance The Grecian thistle was first recorded for New Zealand by Dr. Allan in 1940 (A Handbook of the Naturalised Flora of New Zealand, Department of Scientific and Industrial Research Bull. 83), from Amberley, North Canterbury. His observations were based on specimens collected by M. Skinner (then Inspector of Stock, Amberley) in 1936. The writer’s observations indicate that the thistle has been established in North Canterbury for some years prior to 1936, as it was found to be well established in several localities. - Residents of the Omihi district state that it was originally observed some 20 years earlier along the Home Creek, a tributary of the Omihi Creek, and subsequent to this it appeared in other localities, where the plant is well known to settlers. It has been confused with other thistles, and in North Canterbury passes under the vernacular names of “star thistle,” “variegated thistle,” and “winged thistle,” all of which occur there. As the popular name for this plant in New Zealand the writer suggests Grecian thistle, incorporating the country of origin and avoiding confusion with other thistles already in New Zealand.

Description of Plant The plant is a biennial, producing in the first season a rosette of leaves and in the second season a flowering stem up to 6ft. tall. Root system: a tap root. Leaves: lanceolate, 6 to Bin. long, pinnatifid, with each lobe bearing a pungent spine at its extremity, upper surface dull green to whitish (with cobwebby hairs, and white band along midrib, hence name “variegated thistle”); lower surface whitish with appressed cobwebby hairs. Steins: up to 6ft. tall, on upper plant bearing the heads ■in more or less corymbose arrangement. Heads: up to ljin. diameter, with several rows of spine-tipped bracts, mostly with cobwebby hairs: lowest row of bracts recurved during late flowering or seeding period, and sometimes purplish in colour. Flowers: to l|in. long, purplish. Fruits (“’seed"): brownish, surmounted by pappus of feathery hairs. Distribution in N.Z. The species is restricted to the Waipara and Amberley localities in' North Canterbury, and the actual occurrences are given in the accompanying map.

Habitat Grecian thistle forms distinct communities several acres in extent on rocky areas in modified tussock grassland, as in Mt. Cass and Deans Peaks regions, and on loose rubble and waste land along the Waipara River and Weka and Omihi Creeks. The main infestations occurred at altitudes be* tween 1,000 and 2,000 ft., in modified tussock grassland, and were noted on ridge tops and both sunny and shady faces. The writer was unable to find any occurrences on good fertile soil on the flats; - all occurrences on the fiats were either on unconsolidated river-beds or on the stony shallow soils of the lower river terraces. From the behaviour of the plant in North Canterbury it is possible that it would succeed in the drier districts of New Zealand at least; and certainly up to altitudes of 2,000 ft. Fruit (“Seed”) Dispersal Observations indicate that fruits have been carried down by the rivers and creeks along which the plant occurs, giving rise to the infestations along the lower reaches of these waterways. Animal dispersal has been operative also; the illustration of the heads and the description indicate that “seeds” are . well suited to stock dispersal. In the Mt. Cass locality plants were noted

along the mustering tracks from the old-established blocks of thistle down to the shearing shed. The wind would probably disperse the fruits in the neighbourhood of individual plants and large blocks, but no observations have been made of the extent of this method.

Economic Significance

The. writer’s observations agree with the information gathered in North Canterbury that Grecian thistle has been present in the region for at least 20 years, and that the spread has not been excessive. It is probable that it will become more, common on the river-beds and in the tussock grassland, but whether it would establish and spread on arable country cannot be foretold. The occurrence of the plant in rocky and sandy areas is a probable explanation why the plant has not been considered of any great economic importance. The foliage and heads probably cause inconvenience in handling sheep and wool from blocks where the thistle is well established.

Control and Eradication

Little data on control are available in North Canterbury, as little work has been done on these lines. On several properties patches of the thistle have been grubbed out periodically, but in the main no action lias been taken. On some ' ■ tussock blocks the patches are burned off in-

cidentally when the tussock is fired, out the thistle returns. One property owner considers that this firing has caused a marked reduction in the size of the once large patches, but others have not observed any change in the infestations.

It is suggested that individual plants and patches of thistle which occur on dry river terraces and along riverbeds could be grubbed or even scythed to prevent ripening of seed and spread to areas lower down the rivers. Any treatment for the blocks of thistle established in modified tussock grassland is difficult, due to poor access, presence of rocks, and other difficulties of terrain. Since there is no apparent direct loss occasioned by the existence of patches of several acres of the thistle, it would not be easy to reconcile expenditure of labour and money for eradication. Possibly grubbing of scattered plants, as is done with nasella tussock, could be carried out. Should the plant appear on the better-class country, control measures as adopted for other biennial thistles should prove successful. '