Prickly Lettuce

Lactuca serriola L.

Synonyms - Lactuca scariola

Family: - Asteraceae.


Lactuca is from the Latin lac or lactis meaning milk and refers to the milky sap.

Prickly Lettuce because the leaves are prickly.

Other names:

Compass plant because the leaves often line up in a north south direction.

Milk Thistle because it exudes a white milky sap when damaged.

Whip Thistle

Wild Lettuce because it is related to the edible Lettuce.


A tall, prickly stemmed, lobed leaved, summer growing annual or biennial plant that has its prickly leaves twisted to lie vertically. The spines are mainly confined to the underside midrib and edges of the leaves. It usually has a single stem that is much branched near the top.



Two. Club shaped. Tip indented. Fine, tiny hairs on top and leaf stalk. Petiole slightly shorter than the blade.

First leaves:

Oval. Tip round. Tiny scattered hairs on top, edges and leaf stalk.


Form a short lived basal rosette. Alternate. Usually twisted near the base to lie vertically. Tend to be oriented in a North-south or east-west direction.

Stipules -

Petiole - Absent.

Blade - Blue green, oval to oblong, waxy bloom, stiff, up to 200 mm long by 100 mm wide with broad, opposite, deep lobes curved down towards the base appearing hooked. Tip round to pointed. Spreading auricles near the base. Spines in the edges, the underside midrib and occasionally on the underside main veins. Midrib pale. Edges irregularly toothed. Upper leaves progressively smaller.

Stem leaves - Clasping with 2 auricles. Alternate, less deeply lobed, twisted to lie vertically. Tip pointed. Spines on leaf edges and on midrib underneath. Often aligned in north south direction. Uppermost leaves small, often without lobes, but with broad auricles.


Erect, stiff, tough, 1500-3000 mm tall, simple or branching. Spines on main veins especially near base, smooth on the branches of the panicle. Otherwise hairless. Exude white sticky sap when broken.

Flower head:

Loose, pyramidal, spike like panicle at the end of the stem with stiff branches, that are spineless with many flower heads. Narrow, cylindrical flower head, 7-15 mm long with 6-35 florets on small branchlets subtended by small, egg to arrow shaped bracts with obvious auricles.


All have 'petals' (ligules). Pale yellow to blue. 7-15 mm long. In a pyramid shaped set of branches at the top of the stem.

Bracts - Leafy, purple tips, overlapping, rough, differing lengths, about 5 rows.

Ovary - Receptacle with no scales.

'Petals' - Pale yellow to blue.

Stamens -

Anthers -


Grey-brown, oval, smooth, achene, 3-6 mm long by 1-3 mm wide, slightly flattened, striped with 5-9 ribs. Ribs rough near the bottom and with short bristle near the top. Long thread like beak on top about as long or rarely longer than the achene. Pappus of many, silky, barbed hairs, 3-6 mm long, that fall off easily.



Stout tap root.

Key Characters:

Stem leaves broadly oblong, twisted, pinnatifid, rigidly ciliate. Heads paniculate. Achenes usually ciliolate towards the summit. Florets pale yellow not darkening on drying or drying to blue.


Life cycle:

Annual or biennial. Germinates autumn to spring growing slowly over winter and producing stems in spring. Flowers in summer.



By seed.

Flowering times:

Summer to autumn in western NSW.

Summer in SA.

December in WA.

Seed Biology and Germination:

Vegetative Propagules:



Forms with less lobed leaves occur which may be incorrectly identified as L virosa.


Population Dynamics and Dispersal:

Origin and History:

Southern Europe, North Africa, Western Asia.

The cultivated lettuce (L. sativa) was probably derived from this species.



Courtesy Australia's Virtual Herbarium



Temperate and subtropical.


Most abundant on heavy soils.

Plant Associations:




Does not host Root Lesion Nematodes (Pratylenchus neglectus or thornei) (63)


Weed of winter and spring crops, fallows, horticulture, gardens, bushland and disturbed areas.


Possibly toxic. Only young plants appear to be toxic.


Loss of appetite, weakness, emphysema.


Remove stock from the infestation. Don't allow hungry stock to graze infestations.



Management and Control:


Eradication strategies:

Herbicide resistance:

Some populations are resistant to group B herbicides.

Biological Control:

Related plants:

Lettuce (L. sativa) was probably derived from Prickly Lettuce.

Wild Lettuce (L. saligna) has narrower lobes and no spines on the stem leaves.

Plants of similar appearance:

Capeweed (Arctotheca calendula) has a light underside and darker upper surface on the leaf.

Dandelion (Taraxacum officinale)

Flatweed (Hypochoeris radicata)

Indian Hedge Mustard (Sisymbrium orientale)

Hawkbit(Leontodon taraxacoides)

Ox tongue (Helminthotheca echioides)

Prickly Lettuce (Lactuca serriola)

Prickly Sow Thistle (Sonchus asper)

Rapistrum (Rapistrum rugosum)

Smooth Catsear (Hypochoeris glabra)

Skeleton Weed (Chondrilla juncea) has backward pointing leaf lobes.

Sow Thistle (Sonchus oleracea)

Wild Radish (Raphanus raphanistrum)

Wild Turnip (Brassica tournefortii)

Slender Thistle (Carduus spp.)

Fleabane (Conyza spp.)


Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P106-107. Photos.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P942.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P398-399. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P718-719. Photos.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P175.

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). P100.

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). #713.2.

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). P688.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P56. Diagrams. Photos.


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