Marrubium vulgare L.
Marrubium is from the Hebrew mar meaning juice and rob meaning bitter and refers to the bitter taste.
Vulgare is from the Latin vulgaris meaning common.
Horehound is a combination of hore referring to the plants white or hoary appearance and hound, which is derived from the Old English hune meaning plant.
White Horehound (UK, USA)
Summary:An aromatic, pale, crinkly and deeply veined, opposite-leaved, bushy, perennial herb with white, woolly hairs and rings of white flowers up the stem from September to May and small spiny burrs with hooks.
Two. Round, 4-5 mm wide, round tip, base notched. Stalk 4-5 mm long. Hairless or hairy blade, long hairs on the stalk. The seedling has a hypocotyl and no epicotyl.
First leaves: Opposite, oval, 5-8 mm long, wrinkled, tip round. Edges lobed. Impressed veins. Fine hairs on upper surface long ones underneath. Stalk 5-8 mm long with dense, matted hairs.
Leaves: Opposite with each pair at right angles to those above and below. Aromatic when crushed. Does not form a rosette.
Petiole - Long, up to 60 mm with hairs.
Blade - Grey, round, 12-50 mm long x 10-60 mm wide, edges irregularly lobed. Lower surface with white, felt like, dense star type hairs and simple cottony hairs and raised veins. Upper surface, bluish green deeply wrinkled with deeply impressed veins and sparse cottony hairs. Leaves are smaller near the top of the flowering stems.
Stems: Erect or spreading, square, 300-1000 mm long, pithy core or solid with a small hole, woody at the base, branch from base and along their length, tufted. Woolly, white hairs that are very dense near the top of vegetative branches. Last year's dead stems are usually present. Root at the nodes where the stems lay on the ground. Aromatic when crushed.
Flower head:In paired, compound, compact clusters that look like they are in rings in leaf axils toward top of stems
Flowers: White. 5 mm long. Stalkless.
Bracts - Rigid, awl shaped, bracteoles that are hairy except at the spiny, bent back tip.
Ovary - Style enclosed in the petals.
Calyx - Tubular, 8-10 nerved, with 10 awl shaped teeth with a hairless, backward curved, hooked tip. Often has longer teeth alternating with shorter ones. Tube, 3-4 mm long, hairy at the opening. Woolly star type hairs. Develops into a burr with hooked spines.
Petals - White, 5-7 mm long, tubular, 2 lipped. Upper lip is erect with 2 oblong lobes. The lower lip is bent back with a large central lobe and 2, small, side lobes. Tube is 3-4 mm long. Hairy on the outside.
Stamens - 4, in pairs, enclosed in petals.
Anthers - With 2 cells almost at right angles.
Fruit:Small, 4 seeded, burr like capsule.
Seeds:Black to grey-brown (with dark spots), 1-2 mm, and smooth to slightly rough, rounded, triangular pyramid to cylindrical or egg shaped.
Roots:Branched and woody taproot with many shallow spreading roots.
Nodal roots on the stem.
Grey wrinkled leaves.
Rings of white flowers.
Perennial up to 1.8 m tall. Seed germinates mainly in autumn with some in winter and spring. Seedlings are initially weak but soon establish and grow rapidly during winter and spring. Some may not flower in their first year whilst others and old plants flower from late spring to autumn. Old season top growth dies off over the next winter and the dead stems remain for some time. New growth is produced each autumn and spring. They are very hardy once they are established.
Reproduction:By seed and stem fragments.
Flowering times:September to January in SA.
October to May in Perth.
Summer and autumn in WA.
Seed Biology and Germination:Produces dormant seed.
Vegetative Propagules:Stems root at the nodes.
Population Dynamics and Dispersal:
Planting in gardens and dumping garden refuse spread it initially.
The spiny hooked burrs attach to animals, bags and clothing and effectively and rapidly spread the seed.
Water spreads the seed along water ways.
The seed will pass through the gut of horses and still germinate.
Heavy grazing increases its abundance.
Seedlings rarely establish in dense pastures, but once established the old plants compete effectively and patches slowly spread.
Commonly spread in fodder and produce.
It tolerates very poor soils and is often a colonising species after erosion events.
Origin and History:Europe. Western Asia. North Africa.
First recorded in SA in 1841 and naturalised by 1848.
Naturalised in Victoria by 1856.
In Tasmania in 1845.
Distribution:ACT, NSW, QLD, SA, TAS, VIC, WA.
In all parts of Tasmania, especially the Midlands.
Widespread in southern Australia.
Courtesy Australia's Virtual Herbarium.
Temperate. Mediterranean. Semi arid and humid temperate. Grows in both high and low rainfall areas.
Soil:Coastal sands, limestone soils and loams. Well drained soils. Tends to be more abundant on alkaline soils.
Medicinal herb used in cough mixtures, for treating skin, ear and eye disorders, worms and constipation. It is a sedative.
Used to make a tea, toffee or brewed into non-alcoholic beer.
Colonises and stabilises eroded soils.
Detrimental:Weed of crops, roadsides, pastures, lucerne, stock yards, farm yards, fence lines, water channels, rabbit warrens and disturbed areas.
Bitter taste makes it unpalatable.
Taints meat that takes a week or two to disappear.
Seed pods cling to, contaminate and mat wool.
Toxicity:Suspected of poisoning sheep.
Legislation:Noxious weed of NSW, SA, TAS, VIC and WA.
Management and Control:Thresholds:
Isolated plants should be manually removed before flowering.
Larger areas should be burnt then cultivated in late spring or early summer. Repeat cultivation to control seedlings or use herbicides. Plant a competitive crop or pasture and use herbicides or spot spray to kill remaining or emerging plants.
Encourage competitive pastures and graze lightly.
Goats are more effective than sheep in grazing situations because the are less selective and tend to eat more of the seedlings.
A number of herbicides are available for use in various situations.
Herbicide resistance:Biological Control:
The bright orange and black horehound bug Agonoscelis rutila is often seen on Horehound in large numbers but doesn't provide significant control.
Related plants:Black Horehound (Ballota nigra ssp. foetida) is in the same family and has a strong, unpleasant odour and purple flowers.
Plants of similar appearance:References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P179. Photos.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P732.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P314-316. Diagram.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P573. Photo.
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P382.
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P170- 171. Photo.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P84-85. Diagrams.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #800.1.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P562.
McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P77. Diagram.
Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P123-125. Photo.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P496-499. Photos.
Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P123. Diagram. Photos.
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