Click on images to enlarge
dense infestation (Photo: Chris Gardiner)
habit prior to flowering (Photo: Chris Gardiner)
habit in fruit (Photo: Sheldon Navie)
lower leaves (Photo: Chris Gardiner)
close-up of leaf underside (Photo: Sheldon Navie)
close-up of upper leaves and hairy four-sided stems (Photo: Sheldon Navie)
young flower clusters (Photo: Chris Gardiner)
branched stems with older flower clusters and immature fruit (Photo: Chris Gardiner)
upper leaves and flowers (Photo: Chris Gardiner)
close-up of flowers (Photo: Sheldon Navie)
close-up of immature fruit (Photo: Sheldon Navie)
clusters of mature fruit with seeds (Photo: Sheldon Navie)
close-up of mature fruit (Photo: Sheldon Navie)
close-up of seeds (Photo: Steve Hurst at USDA PLANTS Database)
Hyptis suaveolens (L.) Poit.
Ballota suaveolens L.
chan, Chinese mint, horehound, hyptis, mint weed, mintweed, pignut, wild spikenard
Labiatae (South Australia)Lamiaceae (Queensland, New South Wales, the ACT, Victoria, Tasmania, Western Australia and the Northern Territory)
Widely naturalised in northern Australia (i.e. in northern and eastern Queensland, in the northern and central parts of the Northern Territory, and in northern Western Australia).
Also naturalised in Papua New Guinea and on several Pacific islands (e.g. Guam, Niue and Hawaii).
Most common in wetter tropical regions, but sometimes also growing in sub-tropical and semi-arid environments. A weed of roadsides, crops and cultivation, pastures, rangelands, grasslands, open woodlands, riverbanks, floodplains, coastal environs, disturbed sites and waste areas.
- an upright and branched herbaceous plant usually growing 1-1.5 m tall.
- its stems are hairy and square in cross-section, while its oppositely arranged leaves have shallowly toothed margins.
- the leaves of this species give off a strong minty smell when crushed.
- its pinkish, bluish-purple or lavender tubular flowers (5-7 mm long) are arranged in 1-5 flowered clusters in the upper leaf forks.
- these small flowers are surrounded by a green tubular structure that turns brown and persists after the flower dies.
- this tubular structure has five lobes, each lobe being topped with a short bristle (about 5 mm long).
Stems and Leaves
The branching stems are green or reddish-green in colour and square in cross-section (i.e. quadrangular) when young. On the upper parts of the plant the stems are about 5 mm thick and somewhat hairy (i.e. pubescent). However, they are often thicker and become slightly woody towards the base of the plant.
The oppositely arranged leaves (2-10 cm long and 1-7 cm wide) are borne on stalks (i.e. petioles) 5-40 mm long. They are egg-shaped in outline (i.e. ovate), oval (i.e. elliptic), or slightly heart-shaped (i.e. cordate). Their margins are shallowly toothed (i.e. crenate or serrate) and they are quite hairy (i.e. pubescent).
Flowers and Fruit
The small pinkish, bluish-purple or lavender coloured flowers (5-7 mm long) are arranged in 1-5 flowered clusters in the upper leaf forks (i.e. axils). They are borne on short stalks (i.e. pedicels) 1-5 mm long and are tubular in appearance with two 'lips' (i.e. they are two-lipped or bi-labiate). The upper lip is divided into two lobes and the lower lip divided into three lobes, with the central lobe having an inflated appearance (i.e. it is saccate). These flowers are surrounded by a green tubular structure that is formed from the five fused sepals (i.e. a calyx tube). It has five lobes, each being topped with a short bristle (about 5 mm long), and turns brown in colour after the flower dies. Flowering occurs mainly from late summer through until late winter.
The fruit is a lobed structure (i.e. schizocarp) that divides into two 'seeds' (i.e. nutlets or mericarps). These 'seeds' (3-4 mm long and 2.5-3 mm in wide) are dark brown to black in colour with whitish markings at one end. They are flattened, shield-shaped and slightly rough in texture.
Reproduction and Dispersal
The fruit readily become attached to animals and clothing and are also dispersed by water, machinery, vehicles and as a contaminant of agricultural produce (i.e. fodder).
Hyptis (Hyptis suaveolens) is regarded as an environmental weed in northern Queensland, the Northern Territory and northern Western Australia. It is listed as a priority environmental weed in two Natural Resource Management regions and is actively managed by community groups in the Northern Territory.
This large woody herb forms dense thickets and has the ability to shade out and displace native vegetation, especially in grazed or disturbed areas, but also in riparian vegetation and on floodplains. It is extensively naturalised in the savannas of northern Australia and was recently listed as one of the weed species posing the greatest threat to rangeland biodiversity in this part of the country.
At some locations along the Normanby and Kennedy Rivers, in northern Queensland, hyptis (Hyptis suaveolens) has been observed to dominate the ground layer with other weed species. While it does not invade the understorey of rainforest vegetation, it has been recorded as a weed of clearings and road and powerline corridors in the wet tropics region of northern Queensland. In the Northern Territory, hyptis (Hyptis suaveolens) has become widespread in the Darwin, Katherine, Gulf and Victoria River Districts and isolated infestations have been found as far south as Barrow Creek.
Hyptis (Hyptis suaveolens) is unpalatable to livestock has the ability to dominate improved and native pastures, especially when they are overgrazed. Hence, this species can significantly reduce the carrying capacity and/or productivity of pastures.
Hyptis (Hyptis suaveolens) is relatively similar to knobweed (Hyptis capitata ), lion's tail (Leonotis nepetifolia ) and horehound (Marrubium vulgare ). These species can be distinguished by the following differences:
- hyptis (Hyptis suaveolens) has pinkish, bluish-purple or lavender coloured flowers that are borne in loose few-flowered clusters in the leaf forks (i.e. axils).
- knobweed (Hyptis capitata ) has white flowers that are borne in small dense globular clusters (15-25 mm across) at the top of stalks (i.e peduncles) 2-9 cm long.
- lion's tail (Leonotis nepetifolia ) has orange flowers that are borne in large stalkless (i.e. sessile) globular clusters (50-60 mm across) in the upper leaf forks (i.e. axils).
This species is declared under legislation in the following states and territories:
- Northern Territory: B - growth and spread of this species to be controlled (throughout all of the Territory), and C - not to be introduced into the Territory.
- Western Australia: Prohibited - on the prohibited species list and not permitted entry into the state.
For information on the management of this species see the following resources:
- the Northern Territory Department of Natural Resources, Environment and The Arts Agnote on this species, which is available online at http://www.nt.gov.au/weeds.
Anonymous (1989). Weeds in Australian Cane Fields. BSES Bulletin No. 28, October 1989. Bureau of Sugar Experimentation Stations, Indooroopilly, Queensland.
Randall, R.P. (2012). A Global Compendium of Weeds. Second Edition. Department of Agriculture and Food, Western Australia. (1125 pp.).
Anonymous (2002). Australia's Virtual Herbarium. http://www.anbg.gov.au/avh. Australian National Botanic Gardens, Environment Australia, Canberra, ACT.
Anonymous (2007). Weeds Australia. http://www.weeds.org.au. National Weeds Strategy Executive Committee, Launceston, Tasmania.
Bostock, P.D. and Holland, A.E. (2007). Census of the Queensland Flora 2007. Queensland Herbarium, Environmental Protection Agency (EPA), Brisbane, Queensland.
Cowie, I. and Kerrigan, R. (2007). Introduced Flora of the Northern Territory. http://www.nt.gov.au/nreta/wildlife/plants/pdf/intro_flora_checklist.pdf. Department of Natural Resources, Environment and The Arts, Northern Territory.
Friend, E. (1983). Queensland Weed Seeds. Queensland Department of Primary Industries, Brisbane, Queensland.
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. The Plant Protection Society of Western Australia, Victoria Park, Western Australia.
Keighery, G. and Longman, V. (2004). The naturalized vascular plants of Western Australia. 1: checklist, environmental weeds and distribution in IBRA regions. Plant Protection Quarterly 19: 12-32.
Kerrigan, R.A. and Albrecht, D.E. (2007). Checklist of NT Vascular Plant Species. http://www.nt.gov.au/nreta/wildlife/plants/pdf/family_checklist.pdf. Department of Natural Resources, Environment and The Arts, Northern Territory.
Lazarides, M., Cowley, K. and Hohnen, P. (1997). CSIRO Handbook of Australian Weeds. CSIRO Publishing, Collingwood, Victoria.
Miller, I.L. and Schultz, G.C. (2002). Hyptis or Horehound (Hyptis suaveolens). Agnote. Weeds Branch, Primary Industry and Fisheries, Northern Territory of Australia, Darwin, Northern Territory.
Navie, S.C. (2004). Declared Plants of Australia. CD-ROM. The University of Queensland, St. Lucia, Brisbane, Queensland.
Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious Weeds of Australia. Inkata Press, Melbourne, Victoria.
Smith, N.M. (2002). Weeds of the Wet/Dry Tropics of Australia - A Field Guide. Environment Centre Northern Territory, Darwin, Northern Territory.
Spooner, A., Carpenter, J., Smith, G. and Spence, K. (2007). *Hyptis suaveolens (L.) Poit. Hyptis. FloraBase: The Western Australian Flora. http://florabase.calm.wa.gov.au. Western Australian Herbarium, Department of Conservation and Land Management (CALM), Perth, Western Australia.
Stanley, T.E. and Ross, E.M. (1986). Flora of South-eastern Queensland. Volume 2. Department of Primary Industries, Brisbane, Queensland.
Wheaton, T. (1994). Plants of the Northern Australian Rangelands. Northern Territory Department of Lands, Housing and Local Government, Darwin, Northern Territory.
Wilson, B.J., Hawton, D. and Duff, A.A. (1995). Crop Weeds of Northern Australia: identification at seedling and mature stages. Queensland Department of Primary Industries, Brisbane, Queensland.