Invasiveness Assessment - Horehound (Marrubium vulgare) 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 Horehound.

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: Horehound
Scientific name: Marrubium vulgare

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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