Invasiveness Assessment - Horehound (Marrubium vulgare) in Victoria
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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 Horehound.
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
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Common Name: Horehound
Scientific name: Marrubium vulgare
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| Question | Comments | Reference | Rating |
| Establishment | |||
| Germination requirements? | “Most seeds germinate after autumn rains but some germination also occurs through winter and spring”. | P & C (1992 P. 497) | MH |
| Establishment requirements? | “Tolerates full sun, shade of woodland canopy”. | Blood (2001 p. 152) | MH |
| How much disturbance is required? | Invades Mallee communities as well as red gum, black box and grassy woodland, dry coastal vegetation. | Carr et al (1992) Blood (2001 p. 152) | H |
| Growth/Competitive | |||
| Life form? | Perennial herb. Other. | P & C (1992 P. 497) | L |
| Allelopathic properties? | No Allelopathic properties described. |  | L |
| Tolerates herb pressure? | “Because of its bitter taste, horehound is not palatable to stock and is therefore, encouraged by heavy grazing”. | P & C (1992 P. 499) | MH |
| Normal growth rate? | “Able to establish without competition. In contrast, seedlings do not establish in dense pastures”. “Young seedlings are not very competitive but, once established, they make rapid growth”. (P & C 1992 p. 497) | P & C (1992 P. 499) | ML |
| Stress tolerance to frost, drought, w/logg, sal. etc? | “Horehound is relatively drought tolerant”. May be tolerant of some water logging if occurs in channel banks. “Tolerates drought and frost”. | P & C (1992 P. 499) Blood (2001 p. 152) | MH |
| Reproduction | |||
| Reproductive system | “Reproducing by seed”. | P & C (1992 P. 497) | ML |
| Number of propagules produced? | “Mature plants can produce over 20,000 seeds per year”. | Blood (2001 p. 153) | H |
| Propagule longevity? | “May survive in soil for 7-10 years”. | Blood (2001 p. 153) | ML |
| Reproductive period? | Perennial herb. “New growth is produced each year in autumn and spring”. | P & C (1992 P. 497) | H |
| Time to reproductive maturity? | “Plants may or may not flower in the first year, depending mainly on soil fertility”. | P & C (1992 P. 497) | H |
| Dispersal | |||
| Number of mechanisms? | Burr attaches to wool, fur, bag, clothing, etc.: water; “and horses are known to pass the seeds in a viable condition”. | P & C (1992 P. 498) | MH |
| How far do they disperse? | Also burrs attached to sheep responsible for much spread in Australia. “and horses are known to pass the seeds in a viable condition”. | P & C (1992 P. 498) | H |
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© The State of Victoria, 1996 - 2009.
This document was last reviewed on 18/08/2009