Invasiveness Assessment - Amsinckia (Yellow burrweed) (Amsinckia spp.) 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 Amsinckia (Yellow burrweed).

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 - 1026 KB)
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Common Name: Amsinckia (Yellow burrweed)
Scientific name: Amsinckia spp.

Question	Comments	Reference	Rating
Establishment
Germination requirements?	“In the field Amsinckia germinates with the autumn rains (April onwards), and by winter the seed produced in the preceding spring is highly germinable.” Requires autumn temperature and rainfall to germinate.	Connor (1965) p55	MH
Establishment requirements?	Connor (1965) found that, given suitable moisture, seed germination was consistently high under both light and dark conditions (66% and 62% germination respectively). Seed can thus germinate whether buried or exposed.	Connor (1965) p54	H
How much disturbance is required?	While it does occur in lowland grassland & grassy woodland population densities are small. Predominantly, it is a weed of highly disturbed areas such as cereal crops, lucerne, degraded pastures and roadsides.	Carr et al (1992) Parsons & Cuthbertson (2001)	ML
Growth/Competitive
Life form?	Annual herb. Others category.	Parsons & Cuthbertson (2001)	L
Allelopathic properties?	None reported.		L
Tolerates herb pressure?	While one sp. of Amsinckia is toxic particularly to cattle, it is nonetheless grazed. Germination and seed production are staggered through the life cycle of the plant. “Four separate germinations have been noted during this period [autumn].” Seed production is high. This indicates that, while the plant may be eaten, its staggered seed production ensures that plants will continue to flower and to persist through subsequent years.	Parsons & Cuthbertson (2001)	MH
Normal growth rate?	“Early germination and rapid growth give yellow burrweed seedlings a competitive advantage over other species.” Rapid growth rate exceeds that of species of similar life form.	Parsons & Cuthbertson (2001)	H
Stress tolerance to frost, drought, w/logg, sal. etc?	“Plants die with the onset of summer temperatures in late spring or early summer.” Not drought tolerant. Resistance to other stresses not documented. Consider a tender herb.	Parsons & Cuthbertson (2001)	L
Reproduction
Reproductive system	An annual herb. Reproduces sexually. “The species of Amsinckia… belong to the section* Muricatae. Self-pollination is a common feature of reproduction within the Muricatae. Combined with cross-compatibility, this places the group in a very aggressive position.” Self and cross-pollination.	Connor (1965) pp50-51.	ML
Number of propagules produced?	“Amsinckia spp. are prolific seeders producing up to 1600 seeds per plant.” Produces more than 1,000 seeds.	Parsons & Cuthbertson (2001)	MH
Propagule longevity?	“The longevity of seed is not known but, stored indoors, they live for more than 2 years but probably not as long as this in the field.” Seeds survive less than 5 years.	Parsons & Cuthbertson (2001)	L
Reproductive period?	Annual herb. Produces propagules for only one year.	Parsons & Cuthbertson (2001)	L
Time to reproductive maturity?	“Seeds germinate… in autumn. The seedling develops into a rosette from which a flowering stem is produced in mid-winter. Growth is still rapid and flowering commences in August, continuing for about 2 months.” Less than 12 months to produce propagules.	Parsons & Cuthbertson (2001)	H
* A division of a genus; a group of species separated by some distinction from others of the same genus (Source: Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
Dispersal
Number of mechanisms?	“The bristly calyx facilitates dispersal on wool, fur and hair of animals including foxes. Human activities are most important, resulting in spread through the movement of contaminated harvesting equipment, hay balers and seed graders, and the dispersal of contaminated seed, fodder and stock.” Propagules spread by attaching to animals and through normal harvesting activities.	Parsons & Cuthbertson (2001)	MH
How far do they disperse?	As human activities are most important in spreading the seed, it is likely that contaminated produce or machinery will disperse propagules more than 1 kilometre. (see comment above).	Parsons & Cuthbertson (2001)	H

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