Mintweed

Salvia reflexa Hornem.

Synonyms - Salvia lanceolata.

Family: Lamiaceae.

Names:

Salvia is from the Latin salveo meaning to heal or be in good health and was the common name for the culinary herb, Sage
Reflexa is from the Latin reflexus meaning to bend back and refers to the stigma lobes that are bent back over the upper lip of the petals.
Mintweed refers to the minty aroma of the crushed plant.

Other names:

Blue Salvia
Lanceleaf Sage (USA)
Narrow-leaf Sage
Wild Mint.

Summary:

An erect, greyish-green annual with four sided stems, about 500 mm tall and pale blue flowers in loose clusters from October to April. The narrow, opposite leaves are covered with felt-like hairs and have a minty aroma when crushed.

Description:

Cotyledons:

Two.

Leaves:

Opposite pairs. Aromatic.
Petiole - Slender, 3-20 mm long on lower leaves.
Blade - Oblong to narrowly egg shaped, 15-65 mm long x 3-12 mm wide, opposite and paired, soft, greyish to bluish-green with smooth or shallowly, round-toothed edges. Rounded tip, abruptly narrowed at the base. Covered with grey-white, short, curved, stiff simple hairs and becomes hairless on the upper surface with age. Extremely tiny bladder like structures on the upper leaf surface.

Stems:

Grey-green, erect, 150-1000 mm tall, square in cross section, many branched. Young stems covered with grey-white, short, stiff, curved, simple hairs.

Flower head:

Rings (verticillasters) of 1-4 flowered clusters, usually as opposite pairs of flowers near the ends of the branches in loose, interrupted spikes. Flowers on short stalks (pedicels).

Flowers:

Small, blue or lilac.
Ovary - Style forked at the tip with the stigma lobes bent back over the upper lip of the corolla.
Calyx - Cup like, 5-8 mm long, with 2 deep lips, 10-12 ribbed. Hairy on the ribs. Upper lip, erect, smooth edged pointed tip. Lower lip with 2 deep lobes.
Petals - Pale blue, 6-12 mm long, tubular and 2 lipped. Hairy. Upper lip, erect with 2 lobes. Lower lip, twice as long as the upper lip, 3 lobed.
Stamens -
Anthers - Fertile cells about 1 mm long, stay within the flower,

Fruit:

Capsule splitting into four, pale brown to yellow, four angled pyramid nutlets. Held in a persistent covering(calyx).

Seeds:

Cream to fawn, angular, 2-3 mm long x 1-1.5 mm wide, smooth dull surface.

Roots:

Fibrous.

Key Characters:

Leaves narrowly oblong, entire or shallowly sinuate to crenate.
Flowers in 1-3 flowered verticillasters, sessile or shortly pedicellate.
Calyx 2 lipped, upper lip entire
Stamens 2, staminodes absent.
Adapted from B.L. Rye.

Biology:

Life cycle:

Summer growing annual herb. Seeds germinate from August to March after rains. It flowers about 5-8 weeks after emergence and continues until it dies in late autumn to early winter. August germinating plants will flower in 56 days and February germinating plants will flower in 32 days. Very small plants less than 50 mm tall can set seed.

Physiology:

Very responsive to N and P but not K or S.

Reproduction:

By seed.

Flowering times:

Summer to Autumn in western NSW.
October to April in Perth.
Spring and summer in WA.

Seed Biology and Germination:

Spaced plants can produce 73,000-179,0000 seeds per plant.
Seed won't germinate for about 6 months after ripening. Chilling breaks the dormancy.
Germination occurs from 4-30C with an optimum around 27C day and 18C night temperatures.
Germination occurs at moisture (osmotic potential) of -0.4 to 1.4 MPa. It will germinate in considerably drier soils than most other plants.

Vegetative Propagules:

None.

Hybrids:

Allelopathy:

It produces chemicals that reduce the growth and germination of companion plants. These chemicals are washed from glands on the leaves into the soil by rain.

Population Dynamics and Dispersal:

Spread by seed. Seed is moved by flood waters and in mud sticking to animals.
It is often spread as a contaminant of Panicum and millet seed and in bird seed.
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:

Southern USA and northern Mexico.
Introduced to Queensland in fodder during the 1902 drought and naturalised soon after and spread to NSW and Victor7ia.
Introduced to WA in 1950 and eradicated. Other introductions have occurred since then.

Distribution:

NSW, QLD, SA, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Prefers the black or fertile soils in summer rainfall regions.

Climate:

Semi arid. Temperate. Sub tropical.

Soil:

Most abundant on flood plains with grey cracking self mulching clays, black earths and grey to brown heavy textured soils. Also on lighter soils subject to flooding.

Plant Associations:

Open Mitchell grass (Astrebla spp.)and Blue Grass (Dichanthium spp.). Cleared Brigalow and Gidyea (Acacia cambagei) scrubs. Open scrub and grasslands.

Significance:

Beneficial:

Fodder.
Honey plant.

Detrimental:

Weed of summer crops, cultivation, roadsides, pastures and disturbed areas.
Competes with pasture especially when run down or stressed.
Competes effectively with the winter active Phalaris aquatica pastures.
Significant weed of summer crops.
Difficult to remove from the similar sized and weight Panicum seed.
Relatively unpalatable.

Toxicity:

Poisonous to sheep and cattle. Especially hungry stock on dense infestations or recently transported animals usually in early summer or in winter when it becomes more palatable as it dies and loses its strong odour.
Causes nitrate poisoning and contains up to 5% nitrate on a dry weight basis.
Hay containing Mintweed may be toxic.

Symptoms:

Nitrate poisoning.
Affected animals stand apart from the mob, rapid breathing, blue tongue and inner lips, muscle twitching, fall over and can't rise, violently twitch if touched when down, chocolate coloured blood. May last 2-3 days before death.

Treatment:

Nitrate poisoning.
Subcutaneously inject 4% methylene blue at a dose of 10 mL per 45 kg body weight.
Feed hay before droving stock across mintweed infested areas. Don't disturb stock grazing infestations.

Legislation:

Noxious weed of QLD, NSW and WA.

Management and Control:

Summer cultivation before seed has set is partially effective. Seeds have staggered germinations. Early application of hormone herbicides to young actively growing plants is effective but needs repeating for later germinations. Don't graze after spraying because of the risk of poisoning after animals eat the sweetened and nitrate loaded plants.
Establishment of summer active grasses usually prevent re infestation. Mid January planting of Lucerne (Medicago sativa) and Finger Grass (Digitaria eriantha) have been used successfully in summer rainfall areas.
Chlorsulfuron provides good control in cereals.
Atrazine applied at seedling emergence usually gives season long control.

Thresholds:

Cereal crops usually out compete mintweed but it contaminates the grain.
Sorghum and cotton suffer significant losses due to competition.

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)
Sage (Salvia officinalis)
Wild Sage (Salvia verbenaca) has lobed or toothed leaves.

Plants of similar appearance:

Mints, Dead nettle, Stagger Weed, Pennyroyal, Horehound, Marjoram, Basil, Rosemary, Spearmint, Hyssop, Thyme, Stachys, Lions Ear.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P181. Photo.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P575-576. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P385-387. Plate 12.

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.

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). #1083.3.

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.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P82. Diagram.

Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P126-129. Diagrams. Photos.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P503-505. Diagram.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.