Hawkweeds: State Prohibited Weed	LC0376
Keith Turnbull Research Institute, Frankston

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Common name

Hawkweeds

Scientific name

Hieracium spp. Family Asteraceae (daisies)

Status

Hieracium species are proclaimed as a State Prohibited Weed in Victoria. This means that Hieracium spp. are to be eradicated if possible from the State. Hieracium species are also proclaimed weeds in New South Wales, Western Australia and Tasmania and have been classified as prohibited imports by the Australian Quarantine and Inspection Service.

There are between 700 and 1000 world species of Hieracium, mostly native to the Northern Hemisphere in temperate and montane areas, but with some species in South America and southern Africa. No species are native to Australia.

Orange hawkweed Hieracium aurantiacum, native to Europe, is the only species known to have become naturalised in Victoria. Small infestations are known from Falls Creek and Mt Hotham. Other hawkweed species have been available from nurseries and markets and are likely to be present in gardens.

Description

Herbs with milky sap, often hairy, with a basal rosette of leaves. The group is divided into two subgenera: Pilosella, which contains perennial, stoloniferous, often mat-forming species that reproduce sexually, and Hieracium, which contains annual, non-stoloniferous species, that reproduce asexually by seed and produce little pollen. Commonly each species is highly variable and contains several subspecies. Hybrids occur frequently.

Stems – erect, the creeping stolons root readily at the nodes, like a strawberry plant.

Leaves – in a basal rosette or alternate on the stems, entire or toothed, rarely lobed, often hairy.

Figures 1 and 2. Orange hawkweed, Hieracium aurantiacum.

Flowers – small, many combined together into cylindrical to bell-shaped heads (as in other daisies). Like dandelions, the flower heads have only petal-bearing ligulate (ray) florets and lack non-petal bearing tubular or disc florets (eg. as seen in the centre of the sunflower head). Usually yellow but sometimes white, orange or red. Bracts surrounding the flower head are of uneven length, in 1-3 rows; the receptacle (basal part of the flower on which the florets are attached) flat and naked; heads arranged in corymbs or panicles or occasionally solitary.

Seeds – an achene, cylindrical with a truncate apex, 10-15 ribbed, bearing a pappus (parachute) of 1-2 rows of brownish or whitish, fragile bristles.

Roots – fibrous; stout rhizomes present in some species.

H. aurantiacum L. (Pilosella aurantiaca), orange hawkweed. Stoloniferous, 15-40 cm high, with long, spreading hairs; leaves mostly in a basal rosette, stalkless, lance-shaped, up to 15 cm long and 2.5 cm wide, with a wide, pale central vein, sometimes with slightly toothed margins and with very conspicuous simple 1-4 mm long hairs on both surfaces, green; stolons slender, hairy; flowers December to March, heads orange, about 15 mm, bracts black-tipped and with glandular hairs, inflorescence commonly of 5 to 10 or more heads in a tight cluster at the top of the stem; flowering stems erect, hairy, usually leafless, sometimes with up to four small leaves near the base; seeds dark brown or purplish black, up to 2 mm long with dingy white, non-feathery pappus hairs up to 6 mm long. Weed in New Zealand and North America.

H. caespitosum Dumort., field hawkweed. Leaves 5-20 cm long, elongated at base, with long hairs; stems 30-50 cm high, with -1-3 leaves, bearing 3-50 flower heads, flowers yellow.

H. lepidulum (Stenstr.) Omang, tussock hawkweed.

H. pilosella L. (Pilosella officinarum), mouse-ear hawkweed. Stoloniferous, mat-forming, usually with many long, slender, leafy stolons; to 30 cm high; leaves mostly in a basal rosette, oblong or oblanceolate to spoon-shaped, to 12 cm long, entire, bristly, with long pale hairs and a dense matt of star-shaped hairs on the underside when young; flowers heads to 25 mm diameter, usually solitary, bracts around the flower head hairy, flowers pale yellow, often with a red stripe; seeds purplish-black. Weed in North America and Europe. The worst species in New Zealand. A potential alpine invader in Australia.

H. praealtum Vill. ex Gochnat, king-devil hawkweed. Generally a mat-forming perennial, 15-45 cm high; with slender, leafy stolons; leaves mostly basal, lance-shaped, 10-15 cm long, bluish-green on the upper surface with 3 mm long hairs; flowers yellow, heads to 20 mm diameter, on stems up to 30 cm high, few to many (up to 25) heads per stem, up to 3 small leaves per stem.

Properties

Hawkweeds are potentially extremely serious weeds, particularly for the tussock grasslands of the tablelands of south-eastern Australia. They are major environmental and pasture weeds in montane and subalpine areas in New Zealand, in upland pastures in North America, and in Japan and Patagonia.

They tolerate poor soils, thrive in overgrazed areas and are difficult to control. In native grasslands they can occupy the entire space between existing tussocks and may subsequently displace the grasses themselves.

Hawkweeds are closely related to dandelions and sow thistles and release chemicals that inhibit the growth of other plants. Hawkweeds grow from wind-dispersed seeds to form very dense patches, which spread by lateral growth of stolons and daughter plants.

Spread from garden specimens, dumping of garden waste and mail order seeds are likely sources of new hawkweed infestations.

Predictions based on climatic requirements and land characteristics indicate that at least H. aurantiacum and H. ramosissimum and other species with similar properties and biology such as H. pratense, H. x floribundum and H. piloselloides could be highly invasive in Victoria.

Management

The Department of Primary Industries is responsible for the control of State Prohibited Weeds. Please provide details of any occurrences of Hieracium spp. to a Catchment Management Officer at a local office of the Department. Manual and chemical control measures will be used on infestations.

References

Blood, K. (2001) Environmental Weeds – A Field Guide for SE Australia. Mt Waverley, C.H.Jerram Science Publishers.

Groves, R. (1996) Hawkweeds. Australian Quarantine and Inspection Service, Pest Leaflet.

Morgan, J. (2000) Orange hawkweed Hieracium aurantiacum L.: a new naturalised species in alpine Australia. Victorian Naturalist 117(2), 50-51.

Roy, B., Popay, I., Champion, P., James, T. and Rahman, A. (1998) An Illustrated Guide to Common Weeds of New Zealand. Canterbury, NZ, New Zealand Plant Protection Society.

Sell, P.D. and West, C. (1976) Hieracium L. Pp. 358-410 in T.G. Tutin et al. (Eds.) Flora Europaea Volume 4. Plantaginaceae to Compositae (and Rubiaceae). London, Cambridge University Press.

Webb, C.J., Sykes, W.R. & Garnock-Jones, P.J. (1988) Flora of New Zealand Volume IV. Naturalised Pteridophytes, Gymnosperms, Dicotyledons. Christchurch NZ, DSIR.

Acknowledgements

Compiled by Ian Faithfull. Figures 1 and 2 by Kate Blood, copyright 2001 CRC for Weed Management Systems.

This publication may be of assistance to you but the State of Victoria and its officers do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.