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Hieracium aurantiacum

Description
 

Orange Hawkweed (Hieracium aurantiacum) is a hairy herb with leaves in a basal rosette. When broken, its stems and leaves exude a milky sap. Individual plants spread via lateral leafy shoots (stolons) which take root and produce new leaf tufts. Its leaves are in basal tufts, about 150 mm long and 30 mm wide, broadest slightly above midway and lacking a conspicuous stalk. The margins entire or indistinctly toothed. Both leaf surfaces bearing fine, spreading hairs about 4 mm long.

Its flower heads are quite densely clustered at the end of an erect leafless stem about 350 mm long which is covered with spreading hairs. Each flower head is about 15 to 30 mm in diameter, consisting of several rows of bright reddish-orange florets, all surrounded by one or two rows of narrow green bracts up to 8 mm long.

In fruit, the heads become more distinctly stalked and separated. Orange Hawkweed seeds are narrow-linear I shapes, about 2 mm long and become airborne through the development of a pappus (a parachute like ring of silky hairs) about. 6 mm long (Tutin et al. 1976).

For further information and assistance with identification of Orange Hawkweed contact the herbarium in your state or territory.

Distribution:

Orange Hawkweed is established in Kosciuszko National Park in New South Wales, near Round Mountain. In Victoria it has spread from Falls Creek Alpine Village to surrounding alpine and subalpine vegetation, at least as far as Basalt Hill, approximately 4 km southeast from the village, and has also been found at Mt Buller. In Tasmania, it has established in the Central Highlands and Southern Midlands, and around Hobart where the largest infestation occurs in the vicinity of the suburb of Fern Tree at the foot of Mt Wellington. It has also been noted at Snug, some 20 km south of Fern Tree (Morgan 2000; Walsh 2007, pers. comm.).

Habit:Herb
Key points:
  • Orange Hawkweed (Hieracium aurantiacum) has a widely known reputation for aggressively spreading, particularly in cool-temperate, often high altitude, areas through the world (e.g. U.S.A., Britain, Canada, New Zealand, mainland Europe away from its natural range).

  • To date, occurrences of Orange Hawkweed in Australia are relatively few and localised.

  • It has been shown to be able to invade intact native vegetation as well as establishing in disturbed sites.

  • Orange Hawkweed spreads by runners over short distances and seed over larger areas
How it spreads:

Hawkweeds spread by both runners and seed, with a one square metre mat producing up to 40 000 seeds a year (CRC 2003). Runners begin to grow from buds in the rosette leaves when the plants are flowering. Depending on growing conditions, plants produce between four and eight leafy runners that can reach lengths of 100-250 mm. These runners form new rosettes and, once established, the patch continues to expand until it covers the site with a solid mat of rosettes. Under ideal conditions, it can form a colony up to 0.5 m cross in its first year. Hawkweeds regrow each year from short, below-ground rhizomes (CRC 2003).

Long-distance dispersal occurs via the wind-blown seeds. Small, presumably young, colonies near Basal Hill, 4 km southeast from Falls Creek Alpine Village, suggest a dispersal range of at least this distant. The seed is clearly viable and able to establish in undisturbed sites, although many infestations are from disturbed sites. A project to map the distribution and spread of the weed in Hobart indicated that movement of seed via water dispersal was also another likely means of dispersal. Other outbreaks have been associated with movement of machinery, so it is likely that seed is carried with soil etc caught on vehicles and soil-moving equipment.

The occurrence in Kosciuszko National Park may be a result of either long-distance wind-dispersal from an unknown source, or the inadvertent transport of seed on hikers' boots or from vehicles or equipment that may have been in the vicinity of populations in Victoria.. The plants' ability to spread vegetatively by producing 'runners' (stolons) enables it to quickly occupy significant areas of vegetation once established. Movement of soil that contains plant fragments is another mechanism by which the plant may spread (Walsh 2007, pers. comm.).

Where it grows:

Hawkweeds grow naturally in temperate and mountain areas and in Australia, Orange Hawkweed has been recorded establishing in cool areas where the annual rainfall exceeds 1300 mm. Recorded sites on the mainland are all above 1500 m altitude, occurring on alpine humus soils in both disturbed and undisturbed sites supporting Snow Gum (Eucalyptus pauciflora) woodlands or grasslands/open heathlands dominated by snowgrass (Poa) species and low shrubs such as Grevillea australis, Hovea montana and Leucopogon species.

In Tasmania it is known from lower altitudes, down to at least 400 m at Fern Tree, a suburb of Hobart, but also at higher altitudes on the Central Highlands. It may be found on soils derived from a range of parent materials including schist, basalt, dolerite and granite (Walsh 2007, pers. comm.).

Flower colour:Orange
Distribution map: Weed Distribution Map
Impacts:

Orange Hawkweed is on the Alert List for Environmental Weeds, a list of 28 non native plants that threaten biodiversity and cause other environmental damage. Although only in the early stages of establishment, these weeds have the potential to seriously degrade Australia's ecosystem.

Loss of botanical biodiversity is perhaps the greatest potential impact of Orange Hawkweed. Its ability to quickly establish and spread is evident from the relatively few known outbreaks to date, attributes that are typical of other species of the genus which have become very serious environmental weeds in other countries. In New Zealand, Hieracium pilosella and H. lepidulum have been reported to displace intertussock vegetation in Festuca-dominated montane and subalpine moorlands (Rose et al. 1995).

It is conceivable that it would successfully compete with native herbs that occupy inter-tussock spaces in alpine and subalpine grasslands and woodlands, several of which are regarded as rare and/or threatened in Australia (e.g. some Euphrasia species, Euchiton species, Pelargonium helmsii etc.). Outside of natural areas, the species is capable of being a significant weed in lawns, gardens etc (Morgan 2000; Walsh 2007, pers. comm.).

It is likely to impact indirectly on livestock by displacing potentially more nutritious pasture species.

Origin:

Orange Hawkweed is common and widespread in North and Central Europe, extending to southern France and Bulgaria (Tutin et al. 1976). It is also established as a weed in the U.S.A., Canada, Britain, New Zealand and some parts of continental Europe outside its natural range (Morgan 2000).

History:

According to records at the National Herbarium of Victoria, Orange Hawkweed has been grown as a garden plant in Tasmania since at least 1948, but was first reported as having escaped there in 1963 (CRC 2003). It was recorded as spreading from amenity plantings in the Falls Creek Alpine Village, Victoria, in 1999 (specimen records at the National Herbarium of Victoria), and then reported in intact native vegetation at least 4 km distant from the village by 2003. In New South Wales it was unknown as a weed until 2003 when a large infestation was noted in Snow Gum woodland near Round Mountain, Kosciuszko National Park, remote from any habitation (Walsh 2007, pers.comm.).

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This database is designed to provide information, including biological and ecological, on invasive plant species that are on a national weed list, or are legislated against in a state or territory. While reasonable efforts have been made to ensure the accuracy of the information, no guarantee is given, nor responsibility taken, by the Commonwealth for its accuracy, currency or completeness. The Commonwealth does not accept any responsibility for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the information contained in this database. The information contained in this database does not necessarily represent the views of the Commonwealth. This database is not intended to be a complete source of information on the matters it deals with. For further information on the images contained in the database please contact the copyright owner. All images in the weed identification tool are managed by the Australian Plant Image Index (APII). Various copyright conditions apply for these images. For further information on the copyright conditions of images contained in the database please contact the APII at: photo@anbg.gov.au.