Dead Nettle

Lamium amplexicaule L.

Family: Lamiaceae.

Names:

Lamium is Latin for some species of Dead Nettle.
Dead Nettle because it looks like Stinging Nettles but doesn't have the sting.

Other names:

Henbit.

Summary:

A square and hollow stemmed, opposite leaved, hairy, annual to biennial herb with clusters of about 12 pink-purple tubular flowers in rings in the upper leaf axils.

Description:

Cotyledons:

Two. Oval, 5-6 mm at right angles to its vertical 6-10 mm stalk. Blade hairless, stalk has short hairs. Round tips. Base notched. The seedling has both a hypocotyl and epicotyl.

First leaves:

Opposite. Oval 5-10 mm with 6-10 mm leaf stalk that elongates as the leaf matures. Tip round. Edges lobed. Prominent veins. Hairs on the blade and stalk. The early leaves often lack the third side lobe normally found on later leaves.

Leaves:

Opposite in pairs. Each pair is at right angles to the pair below it. It does not form a rosette.
Stipules -
Petiole - Slender and square on lower leaves.
Blade - Broadly egg shaped 10-40 mm, Edges with rounded lobes. Sparse fine hairs. Basal leaves, 10-20 mm long.
Upper leaves - Opposite, circular to kidney shaped, 20-40 mm long, clasp the stem so as to join with opposite leaf and completely encircle the stem. Leaves held at more than 900 to the stem. Sparse fine hairs on both surfaces. Edges with rounded lobes. Embrace or cup the rings of flowers.

Stems:

Low lying with the ends curving upwards or erect, up to 400 mm long, hollow, square with ridges at the corners often purplish. Sparse, downward pointing hairs or hairless. Branched from the base and sometimes along their length. Often purplish.

Flower head:

About 12 flowers clustered in the axils of the rings (whorl) of upper leaves.

Flowers:

Almost stalkless. Self fertilising (cleistogamous) flowers are often found early in the season or on some forms.
Ovary - Stigma split in two for about half its length.
Sepals - 4-5 mm long with 5 short, awl shaped, often purplish teeth, striped. Hairy.
Petals - Pink to purplish, with a 15 mm long slender tube that is broadened in the upper third. Upper lip hooded, smooth edged with purple glandular hairs on the outside. Lower lip with 2 very small side lobes and a broad central notched lobe.
Stamens - 4 with the lower pair longer than the upper pair.
Anthers - Bearded. Cells almost at right angles to each other. Open by a common slit.

Fruit:

A group of 4, three angled, pear shaped brown nutlets at the base of the persistent calyx tube. White spots on the inner faces.

Seeds:

Small. 1 mm. Brown (with white spots on inner faces). Triangular pyramid.

Roots:

Taproot.

Key Characters:

Upper stem leaves sessile and completely encircle the stem. Corolla tube has no hairs inside.
Opposite leaves, lobed and hairy.
Stems hollow and square.
Purple pink flowers.

Biology:

Life cycle:

Annual or biennial. Germinates from autumn to spring. In Tasmania the main germination is in spring and in NSW, Victoria and WA the main germination is in autumn. Flowers late-winter/spring

Physiology:

Reproduction:

By seed.

Flowering times:

Most of the year in western NSW.
Most of the year in SA.

Seed Biology and Germination:

Vegetative Propagules:

None.

Hybrids:

A cleistogamous variety clandestinum occurs in SA that has shorter petals that don't open.

Allelopathy:

Population Dynamics and Dispersal:

Origin and History:

Europe, NZ, Western Asia and North Africa

Distribution:

ACT, NSW, QLD, SA, TAS, VIC, WA.
Common in parts of the South, North-East and North-West with little in the Midlands of Tasmania.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate.

Soil:

Plant Associations:

Significance:

Beneficial:

Detrimental:

Weed of crops, vegetables, winter cereals, fallows, pastures, roadsides, gardens, horticulture and disturbed areas.

Toxicity:

Mainly in sheep but horses and cattle also affected. Field cases are usually associated with stock grazing mature plants in cereal stubbles. Lambs and fat sheep are most susceptible.

Symptoms:

Staggers occur when stock are driven.
On droving, affected sheep lag behind mob and have stiff hindquarter movements, head pushed forward and back hunched, rapid breathing, shivering and trembling. They may collapse and die if driven harder.
Symptoms appear a week to a month after exposure to Dead Nettle.

Treatment:

Within 2-3 weeks most will recover completely if allowed to rest and are removed from the infestation.

Legislation:

None.

Management and Control:

Thresholds:

Competitive in seedling vegetables and low growing crops.

Eradication strategies:

Herbicide resistance:

Biological Control:

Related plants:

Red Dead Nettle (L. purpureum) is very similar when young but the upper stem leaves are shortly petiolate and don't clasp the stem.

Plants of similar appearance:

Stagger weed (Stachys arvensis) has a shorter and thicker petiole on the cotyledons and young leaves and doesn't have a notch in the base of the cotyledon. Upper stem leaves are more elongated and don't completely encircle the stem.
Speedwell (Veronica spp.) has a shorter and thicker petiole on the cotyledons and young leaves.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P178. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P740. Diagrams.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P315-316. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P572. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P380-381.

Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P82-83. 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). #719.1.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P38. Diagram.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P122. Diagrams. Photos.

Acknowledgments:

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