Invasiveness Assessment - Orange hawkweed (Hieracium aurantiacum) in Victoria (Nox)
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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.
| Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the invasiveness of Orange hawkweed.
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
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Common Name: Orange hawkweed
Scientific name: Hieracium aurantiacum
| Question | Comments | Reference | Rating |
| Establishment | |||
| Germination requirements? | Germination of seeds usually occurs after wet spring periods. | AQIS (1996) | MH |
| Establishment requirements? | Can establish under moderate canopy can grow in open woodlands. (Hieracium sp. In general). “Some species require light to germinate, whereas others do not”. (AQIS 1996). | Callihan et al (1997) | ML |
| How much disturbance is required? | Grow in well-established pastures, open woodlands. However, habitat of this species is open areas. (See notes on ‘habitats’). | Callihan et al (1997) | MH |
| Growth/Competitive | |||
| Life form? | Perennial herb ‘others’. ‘creepers’. Creeping stolons/runners. “Once established as seedlings, hawkweeds usually grow to very dense patches which spread out by the formation of new stolons and daughter rosettes”. (AQIS 1996). Can reproduce from buds on roots. (Callihan et al 1997). Also Geophyte. | AQIS (1996) Tutin et al (1976) Muenscher (1955) | ML |
| Allelopathic properties? | Hawkweed produces phytotxins that inhibit the growth of both herbaceous and tree species (of particular species). | Rice (1984) Randall (1999) | MH |
| Tolerates herb pressure? | Common in pastures where proliferation is common. (AQIS 1996, Callihan et al 1997), also would be capable of rhizome production. | AQIS (1996) Callihan et al (1997) | MH |
| Normal growth rate? | Propagation by runners is vigorous. Rapidly invades new areas, making control difficult. | Fornasori et al (1996) Callihan et al (1997) | H |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerates drought (drought resistant), frost (occurs in mountain areas). Described as ‘hardy’. | Randall (1999) Fornasari et al (1996) | MH |
| Reproduction | |||
| Reproductive system | Reproduces by seeds and runners (rhizomes). | Muenscher (1995) | H |
| Number of propagules produced? | Seeds are produced in large numbers in this genus. up to 40,000 per sq. m. however, per plant = 12 florets per inflorescence x 18 inflorescence per plant = 432 seeds per plant. (Picture Muenscher 1955). | AQIS (1996) | ML |
| Propagule longevity? | Seeds of some species may remain dormant for a few months, however seeds lose viability fairly quickly in soil. | AQIS (1996) | L |
| Reproductive period? | Perennial. The dense mats of plants virtually exclude all other species (form dense monocultures). | Randall (1999) Callihan et al (1997) | H |
| Time to reproductive maturity? | Fast growing herb, which reproduces (vegetively) and probably also sexually (from seed) in 1-2 years from germination. “Once established as seedlings, hawkweeds usually grow to very dense patches which spread out by the formation of new stolons and daughter rosettes”. (AQIS 1996). “Hawkweeds re grow each year from short below-ground rhizomes”. (AQIS 1996). | Callihan et al (1997) AQIS (1996) | MH |
| Dispersal | |||
| Number of mechanisms? | Wind and animals - small seeds (1.5 mm). (Birds feathers, fur). | Randall (1999) | H |
| How far do they disperse? | Small seeds presumably dispersed > 1 km. “Because of their dispersing over long distances, Hieracium spp. Are difficult to control”. “Studies in eastern Canada showed that seeds are not carried far by the wind. Minute barbs along ribs on the seeds enable them to stick to hair, fur, feathers and clothing and vehicles and be carried long distances”. (Callihan et al 1997). | Fornasori et al (1996) CAB Abstract | H |
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