An erect, green perennial with annual tops and four sided stems, about 500 mm tall with lobed, wrinkled, deeply veined, opposite leaves with a minty aroma when crushed. The purple flowers are in 6 flowered rings spaced along the ends of the branches from July to October or in April.
Description:
Cotyledons:
Two. Round. Tip round. Sides convex, Base squarish. Surface hairy. Petiole longer than blade and hairy. Base of blade almost at right angles to the petiole.
First Leaves:
Emerge singularly.
Petiole - About the same length as the blade. Longer than those on later leaves.
Blade - Oval with forward pointing, rounded teeth on the edges. Tapered base. Obvious whitish veins. Hairy.
Leaves:
Forms a rosette. Opposite pairs. Variable. Minty odour when crushed.
Petiole - Slender, 30-50 mm long on rosette leaves. Tapered with flattened edges near the base.
Blade - Oval, oblong to narrowly egg shaped, wrinkled, rough, 20-200 mm long by 3-100 mm wide, networked patterned, indented veins, soft, rounded lobes or teeth on the edges, occasionally with deep lobes that have rounded teeth. Abruptly narrowed at the base. Tip rounded to pointed. Base squarish to indented. Hairless or sparsely hairy but usually hairy on the veins. Aromatic.
Stem leaves - Similar to the rosette leaves, opposite and paired, with almost no petiole and grading into leafy bracts beneath the main flower branches.
Stem Leaves:
Oval 10-200 mm long. Prominent veins. Paired. Clasping. Mainly on the lower portions of the stem
Stems:
Green, 100-1000 mm tall, square in cross section often reddish purple on the angles, many branched. Sparse, simple, multicellular and glandular hairs. Aromatic.
Flower head:
Rings(verticillasters) of 6 flowered clusters, near the ends of the branches and spaced along the stems in loose, interrupted spikes. Flowers almost stalkless. Pair of leafy egg shaped bracts below the rings and where the flowering branches fork.
Flowers:
Small and variable in size, purplish to deep blue or rarely white. Fragrant.
Bracts - Egg shaped, pointed tip, shorter than the calyx.
Ovary - Style forked at the tip with the stigma lobes bent back.
Calyx - Cup like, 5-8 mm long, with spreading glandular hairs, 2 lipped. Upper lip, hairless or almost so between the nerves, 3 small lobes with tiny points and the 2 side lobes arched. Lower lip with 2 tapering tipped lobes on the middle lobe, may have 2 white spots at the base.
Petals - Purplish to deep blue or rarely white, 6-15 mm long, tubular and 2 lipped. Hairless to sparsely hairy. Upper lip, long, hooded arched or straight, longer than the tube. Lower lip, 3 lobed, central lobe broad and concave above a narrow base.
Stamens -
Anthers - Fertile cells about 1.5 mm long, stick out of the flower on a long connector.
Fruit:
Capsule with one to four, black, nutlets. Held in a persistent covering(calyx).
Seeds:
Greyish to dark brown or black, slightly angled on the inner face, ellipsoid, 2-3 mm long by 1-1.5 mm wide, smooth dull surface. Tip rounded. base rounded, edges rounded to flattish.
Roots:
Fibrous.
Key Characters:
Perennial.
Leaves green, narrowly oblong to ovate, crenate, shallow and broad lobes.
Stem with short hairs.
Flowers racemose, 6 flowered verticillasters, sessile or shortly pedicellate
Calyx with short hairs, 2 lipped, upper lip 3 lobed
Stamens 2, staminodes absent.
From J.M. Black and B.L. Rye.
Biology:
Life cycle:
Winter spring growing perennial herb. Seeds germinate from autumn to spring and crowns shoot in autumn and form a rosette over winter and spring crowding out neighbouring plants. Flowering commences in late spring and continues into summer. Plants may remain green well into summer but eventually the top growth dies off by late summer or early autumn.
Physiology:
Reproduction:
By seed and perennial crown.
Flowering times:
Spring to early summer in western NSW.
April in Perth.
July to October or April in WA.
Seed Biology and Germination:
Vegetative Propagules:
Perennial crown.
Hybrids:
Allelopathy:
Population Dynamics and Dispersal:
Spread by seed. Seed is moved by flood waters and in mud sticking to animals.
Tends to form dense local stands excluding most other species.
Tends to take over after denudation due to overgrazing, flooding or cultivation.
Origin and History:
Europe. Mediterranean. Asia.
Distribution:
ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Habitats:
Climate:
Semi arid. Temperate. Mediterranean.
Soil:
Most abundant on sandy soils.
Plant Associations:
Significance:
Beneficial:
Fodder.
Detrimental:
Weed of roadsides, pastures, gardens, cultivation, woodlands and disturbed areas.
Competes with pasture especially when run down or stressed.
Relatively unpalatable.
Toxicity:
Suspected of being poisonous to sheep and cattle causing nitrate poisoning. Especially hungry stock on dense infestations.
Symptoms:
Nitrate poisoning.
Treatment:
Nitrate poisoning.
Feed hay before droving stock across mintweed infested areas. Don't disturb stock grazing infestations.
Legislation:
None.
Management and Control:
Once established it is difficult to control without herbicides. Don't graze after spraying because of the risk of poisoning after animals eat the sweetened and nitrate loaded plants.
Thresholds:
Eradication strategies:
Spray small areas until just wet and a 1-2 metre buffer strip with a mixture of 1 litre of Tordon 75-D in 100 litres of water.
Herbicide resistance:
Biological Control:
Related plants:
Red Salvia (Salvia coccinea)
Mintweed (Salvia reflexa) has leaves with no lobes or very shallow lobes and is a summer growing annual.
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P181. Photo.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P733. Diagram.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P316-317. Diagram.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P576. Photo.
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.
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). #1083.4.
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). P565.
Moerkerk, M.R. and Barnett, A.G. (1998). More Crop Weeds. R.G. and F.J. Richardson, Melbourne. P103. Diagrams. Photos.
Acknowledgments:
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.