Quick Facts

Quick facts

• Originally from Europe, Asia and north Africa, Horehound (Marrubium vulgare) is a mint-like semi-woody herb, to 60 cm tall, branching at the base with many white stems and grey-green leaves.
• Stems and undersides of leaves are white short-woolly-hairy, upper leaf surface is grey-green, leaves 1–3.5 cm long, 1–3 cm wide, with rounded cluster of 10-many spiny calyxes below paired leaves, producing small white flowers.
• It is a widespread weed in southern Australia in both high and low rainfall regions, colonising disturbed sites especially in pastoral areas.
• The seeds develop in a burr-like structure that sticks to the wool of sheep and the fur and feathers of other animals enabling effective seed dispersal.
• Infestations can result in reduced grazing areas available for stock, not normally eaten by stock unless no other fodder is avalible. 
• A contamination of wool, tainting of milk and meat if eaten.
• It is also a very serious threat to natural ecosystems.
• Effective control requires a range of techniques including manual removal, burning, ploughing, chemical applications and biological control.

What Does It Look Like?

What is it?

Horehound (Marrubium vulgare) is an erect, multi-stemmed usually at the base, sofwooded to semi-woody perennial shrub to about 60 cm high. The stems are densely covered with white hairs giving them a grey-white appearance. The leaves have a leaf-stalk 0.2–4 cm long, leaves are more or less round or oval in shape, 1–3.5 cm long, 1–3 cm wide, arranged in opposite pairs, upper surface woolly to glabrescent (hairy loosing hairs becoming smooth with age) finely wrinkled with impressed reticulate venation, and densely covered on the lower surface with white hairs. leaf margin toothed – crenate-serrate to deeply dentate

The flowers are densely clustered at the bases of leaf pairs and are 10–many-flowered with the clusters. Flowers are white to cream,  each flower with a tube of petals, 6–12 mm long surrounded by a densely hairy calyx 4–7 mm long, with 10 hooked lobes about 1–2 mm long, alternating shorter and longer. Stamens are inserted near middle of flowering-tube.

After flowering, the calyx becomes a dry, brown, spiny, burr-like structure that surrounds the fruit and aids in seed dispersal (Conn 1999; Parsons & Cuthbertson 1992; VicFlora 2021). 

For further information and assistance with identification of Horehound contact the herbarium in your state or territory.

Flower colour

White, Cream

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

Horehound occurs in both high and low rainfall districts, particularly on alkaline soils and degraded or overgrazed pasture. It commonly occurs in waste places such as along fence lines, roadsides and channel banks, around buildings and sheep camps and sometimes colonies bare eroded ground. It also invades disturbed sites in natural bush-land (Parsons & Cuthbertson 1992; Conn 1999; CRC 2000; Government of South Australia 2021).

Are there similar species?

Horehound (Marrubium vulgare) is superficially similar to some Mints (Mentha spp) and possibly other members of the Lamiaceae family. It can be confused with Stagger Weed (Stachys arvensis), Dead Nettle (Lamium amplexicaule), Red Deadnettle (Lamium purpureum) and Wild Sage (Salvia verbenaca).

Unlike Horehound the stems and leaves of stagger weed have a few spreading hairs, its 'calyx' tubes have five teeth (not ten), and its flowers are pale purple or pinkish in colour (not white). 

Dead nettle has stalkless (sessile) leaves along the flowering stems (these leaves are stalked in Horehound) and its stems and leaves are usually sparsely hairy. Its 'calyx' tubes have five teeth, and its flowers are pink, purple, bluish or reddish in colour. 

Red deadnettle stems and leaves are also usually sparsely hairy, its 'calyx' tubes have five teeth, and its flowers are reddish-purple in colour. 

The leaves of wild sage along the flowering stems are almost stalkless (sub-sessile) and have shallowly toothed margins. Its stems and leaves are sparsely hairy, its 'calyx' tubes have two 'lips' (the lower with two teeth), and its flowers are dark purple or bluish in colour (Navie 2004).

Why Is It A Weed?

What are its impacts?

Agriculture: Horehound is a major pasture weed. It causes wool quality losses due to contamination by burrs. It is not palatable to stock and is therefore favoured by heavy grazing which reduces competition by palatable plant species. This leads to plants of Horehound occupying large areas of pasture and a considerable reduction in the area available for stock grazing. If animals are forced to eat it due to a lack of alternative feed their meat and milk are tainted (Parsons & Cuthbertson 1992; Conn 1999).

Native ecosystems: Horehound is also a very serious threat to natural ecosystems, especially if they have been disturbed, overgrazed or previously grazed by sheep. It invades a range of indigenous vegetation types including dry coastal vegetation, mallee shrubland, lowland grassland and grassy woodland and vegetation on rock outcrops (Carr et al. 1992; CRC 2000) from temperate to semi arid environments.

How does it spread?

The burr-like calyx of Horehound is an effective adaptation for dispersal of the seeds by animals. Sheep are a major dispersal agent because the burrs stick to their wool. The burrs also adhere to the fur of kangaroos and rabbits, the feathers of emus and to human-made objects such as clothing, bags and tyres. The seeds are also dispersed by water, as a contaminant of fodder and through horses droppings (Parsons & Cuthbertson 1992; CRC 2000).

What is its history in Australia?

The main period of introduction to Australia was around 1830 when Horehound was brought to Australia as a garden and medicinal herb and for use in beer brewing (CSIRO European Laboratory 2001; CRC 2000). The first introduction may have occurred earlier when a specimen was sent to New South Wales from Europe by Joseph Banks in 1798 (CRC 2000). It was first recorded in South Australia in 1841, considered naturalised in that state by 1848 and in Victoria by 1856. Many infestations had their origins in farm gardens, often when a house was abandoned or when garden waste was discarded (Parsons & Cuthbertson 1992).

How To Manage It?

Best practice management

Control of Horehound requires a combination of different techniques for best results.

Non-chemical control: Manual removal is suitable only for small patches because it is so labour intensive. Larger infestations can be burned to stimulate seed germination and the resulting plants ploughed and buried before they flower (Parsons & Cuthbertson 1992; CRC 2000).

Chemical control: A range of herbicides are considered suitable for control of this weed for various application marthods, see (CRC 2000; DPI, NSW 2019; Invasive Species Unit, Biosecurity SA 2018; DiTomaso, et al. 2013; Government of South Australia 2021; HerbiGuide 2021). Please see the Australian Pesticides and Veterinary Medicines Authority for further chemical information.

Biological control: Horehound has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. Four insect species have so far been identified as potential biological control agents. Two of these have already been released, the Horehound Plume Moth Wheeleria spilodactylus and the Horehound Clearwing Moth Chamaesphecia mysiniformis. Wheeleria has established well and its leaf-eating caterpillars are producing good results in terms of biomass and seed reduction (CRC 2000; CSIRO European Laboratory 2001).

Does it have a biological control agent?

YES

When does it grow? (lifecycle/growth calendar)

The seeds of Horehound germinate primarily in autumn in response to rainfall. In higher rainfall areas (400+ mm), seed will germinate at other times if sufficient rainfall occurs. Flowers are produced mainly in spring but can occur at other times in higher rainfall areas. Burrs and seeds are produced mainly in summer. The main growth periods are in spring and autumn (CRC 2000).

Where Is It Found?

Which states and territories is it found?

ACT, NSW, QLD, SA, TAS, VIC, WA

What areas within states and territories is it found?

Horehound is widely naturalised in southern Australia and extends as far north as southern Queensland. The heaviest infestations are found in north-western Victoria and south-eastern South Australia where semi-arid conditions contribute to decreased vigour of competing plant species (CRC 2000). It is also a widespread and troublesome weed in pastoral areas of New South Wales, Tasmania and southern Western Australia (Parsons & Cuthbertson 1992).

Because of its invasive nature and early introduction, Horehound has probably reached the limits of its potential distribution in Australia (CRC 2000).

Where does it originate?

Horehound is native to southern and western Europe, central and western Asia and north Africa (Parsons & Cuthbertson 1992).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

SA, TAS, VIC

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Marrubium vulgare

Other scientific names (synonyms)?

Does it have other known common name(s)?

White Horehound, Hoarhound, Marrube, Houndsbane, Piripiri, Bidi Bid, Aykriha, Shaher, Hkash el Kalb