Description
The Orange Hawkseed weed.
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.
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.
Habit:
Close up of Orange Hawkseed
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. 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, belowground rhizomes.
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.
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.
Flower colour:
Orange
Distribution map:
Map of Current Distribution and Potential Distribution of Weed
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.
Origin:
Orange Hawkweed is common and widespread in North and Central Europe, extending to southern France and Bulgaria. 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.
