Hyssop Loosestrife

Lythrum hyssopifolia L.

Family: - Lythraceae.


Lythrum I is from the Greek lythron meaning gore.

Hyssop Loosestrife

Other names:

Lesser Loosestrife

Small Loosestrife

Hyssop-leaved Loosestrife



A hairless, weak, red and ribbed or squarish stemmed annual or occasionally biennial herb with many narrow, oblong leaves and single, tiny, pink to purple, 5 petalled, tubular flowers in the axils from October to December.



Two. Oval. Tip rounded. Sides convex. Base tapered. Hairless. No petiole.

First leaves:

Oval, opposite, tip rounded, at right angles to the pair below and above, hairless.


Mainly alternate, some opposite.

Stipules - Absent.

Petiole - Short or none.

Blade - Dark green, oblong, 5-40 mm long by 1.5-6 mm wide. Tip rounded. to flat. Sides convex to almost parallel. Base tapered. Surface hairless.


Low lying or turned upwards at the ends, weak, soft, often reddish, 100-600 mm long, ribbed, somewhat angular or square, branch from the base. Hairless.

Flower head:

Mainly single flowers on a short stalk (pedicel) in the upper leaf axils and often in the lower leaf axils also. Two tiny membranous bracts in the middle of the peduncle.


Almost stalkless.

Bracts -

Ovary - Superior, enclosed in floral tube. Receptacle is tubular with the lower half often delimited by a constriction and is 2.5-3.5 mm long by 1 diameter at the throat, increasing to 4-6 mm long by 1.5 mm diameter and held close to the stem when in fruit.

Sepals - -4-6, green, broad, erect, membranous, < 1mm long and narrowly triangular with 4-6 longer, green, lance shaped appendages.

Petals - 4-6, pink, red-blue or purplish, 1-2 mm long, about half as long as the receptacle.

Stamens - 2-12 usually 4-6, enclosed, don't exceed the sepals. On one side of the petal tube.

Anthers - 0.25 mm long, versatile, 2 parallel cells, releases pollen by a lengthwise slit.


Oblong, 2 celled capsule, enclosed in the swollen receptacle (torus) held close to stem. 5 mm long by 1.5 mm wide.


Grey, oval to tear or irregularly shaped, less than 1 mm diameter. Surface shiny, smooth and dimpled.



Key Characters:

Small flowers. Low lying stems. Petals about 2 mm long. Hairless. Sepal appendages longer than sepals.


Life cycle:

Annual herb, sometimes biennial. Germinates in autumn and winter and grows into summer until the soil dries. Starts flowering in spring.



By seed.

Flowering times:

Summer in SA.

Summer in western NSW.

October to December in Perth.

Late spring to summer in WA.

Seed Biology and Germination:

Vegetative Propagules:




Population Dynamics and Dispersal:

Varies considerably between seasons. Most dense in wet years.

Origin and History:

Cosmopolitan. May be native to eastern Australia.





Temperate. Mediterranean. Higher rainfall areas.


Low lying damp soils, flood plains and summer irrigated land.

Plant Associations:



Low palatability fodder.

Used in herbal medicine.


Weed of wet areas in pasture, irrigated summer crops, orchards, vineyards, streams, swamps, fallows, rice, stubbles gardens and disturbed areas.


It has been implicated in occasional large mortalities of sheep grazing stubbles in summer in SA, Victoria and NSW. It causes severe hepatic(liver) and renal(kidney) tubular necrosis. In 1998, it was implicated in a similar case near Albany, WA. It is thought that the late senescence or greenness of this plant in summer stubbles may contribute to its attractiveness to stock during this time.



Management and Control:


Eradication strategies:

Use sulfonylurea herbicides.

Herbicide resistance:

This plant is more tolerant to glyphosate than most others.

Biological Control:

Related plants:

Mediterranean Loosestrife (L. junceum)

Purple Loosestrife (L. salicaria) is a major environmental weed in the USA.

Plants of similar appearance:


Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P183-184. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P599. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P262.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P509. 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). P174. 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). #782.2.

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). P366-367. Diagram.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P125. Diagrams. Photos.


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