Camel Melon

Citrullus lanatus (Thumb.) Matsumura & Nakai

Synonyms - Citrullus vulgaris, Colocynthis citrullus, Cucurbita citrullus.

Family: Cucurbitaceae.

Names:

Citrullus is from the Latin word citrus for the citron tree and is probably applied because the fruits are a similar size and colour.
Lanatus is the Latin word for woolly referring to the woolly hairs on the plant.
Camel Melon refers to its association with the camel routes in Australia as does Afghan Melon because Afghans commonly operated the camel trains.

Other Names:

Afghan Melon (WA)
Bastard Melon
Bitter Apple (South Africa)
Bitter Melon
Mickey Melon
Pie Melon
Tshiama (South Africa)
Wild Melon
Wild Water Melon
Many other colloquial names.

Summary:

A hairy, trailing, summer growing, annual vine to several metres wide with yellow male and female flowers in late summer to autumn and mottled, green melons about 120 mm in diameter. It has branched tendrils and large, deeply lobed leaves with a relatively strong unpleasant odour when crushed.

Description:

Cotyledons:

Two. Oval. Tip notched. Sides convex. Base tapered. Hairless. Short stalk. Obvious light veins.

First leaves:

Round in outline, tip round, base notched, Tend to be 3 lobed. Edges toothed. Obvious veins. Hairless on top. Sparse hairs underneath.

Leaves:

Alternate.
Tendrils - Long. 2-4 branched, about half way down their length, rarely simple, usually 2 branched or forked.
Petiole - Yes. With bristly hairs that are shorter than the leaf hairs. Rough to touch. Shorter than the blade.
Blade - Egg shaped to triangular to heart shaped. 20-200 mm long x 20-150 mm wide. Notched at the base with 2-4 opposite, deep, egg shaped to narrow lobes and 1 central lobe. These lobes, especially the central one, are sometimes toothed or lobed again. The middle lobe is the longest. Hairy on top initially and becoming hairless with age. Hairs or bristles, with a warty base, underneath with longer hairs on the veins and rough to touch. Tip notched or with a short sharp point. Pale veins.

Stems:

Trailing, prostrate. Up to 2000 mm long. Bristly hairs often woolly towards the ends. Rough to touch.

Flowers:

Male and female flowers on the same plant. Yellow, 5 petalled and 30-40 mm diameter.
Male flowers single on hairy stalks, 5-80 mm long arising from leaf axils. Female flowers single on hairy stalks, 3-35 mm long arising from leaf axils.
Bracts - at base of inflorescence, egg shaped to spade shaped, 3-20 mm long.
Ovary - Hairy, 6-12 mm long. Inferior. Hairy receptacle.
Sepals - Tubular near the base. Tube 3-4 mm long with lobes that oval to egg shaped, 3-5 mm long.
Petals - 5. Yellow. Hairy or woolly. Tubular near the base. Tube 3-4 mm long with egg shaped to oblong, pointed tip lobes, 5-16 mm long x 30-40 mm diameter.
Stamens - Looks like 3 with 3 free filaments in the male. 3 small staminodes surrounding the style in the female.
Anthers - Without an appendage, but margins with broad, rounded lobes.

Fruit:

Green globular or oblong melon with paler or white longitudinal rows of spots. 60-150 mm diameter. Hairy initially becoming hairless. Flesh white and firm. Bitter to taste.

Seeds:

Many, 5-12 mm long, 6 mm wide. Egg shaped to oval, narrowed towards the base. Flattened. Initially white and turn brown with black stripes at maturity. Surface is slightly roughened and hairless. Seeds eaten by parrots, cockatoos and galahs.

Roots:

Stout taproot with many, strong, spreading laterals.

Key Characters:

Forked tendrils. Distinctive odour when crushed.. Smooth, mottled melons about 100 mm in diameter. Summer vine with yellow flowers.

Biology:

Life cycle:

Annual. Seeds germinate in spring and summer after rains and form a large vine, if moisture is available. Flowers and sets fruit from late summer to autumn. Vine dies in autumn to early winter.

Physiology:

Once established they are very drought tolerant and nearly always set melons and seed. They are often the only plant surviving the summer drought.
Emits a strong odour when crushed which makes the vines unattractive to stock.

Reproduction:

By seed.

Flowering times:

November to April in SA.
Summer to autumn in NSW.
February to May in Perth.

Seed Biology and Germination:

Germinates readily in warm soils where adequate moisture is present.
May remain dormant in the soil for several years.

Vegetative Propagules:

None.

Hybrids:

Many. Cultivated hybrids include the Water Melon and Pie Melon.

Allelopathy:

Population Dynamics and Dispersal:

Infestations vary considerably between years probably due to seasonal conditions.
Seed is retained in the dried fruit that is blown in the wind and floats in water. Fruits are also spread by road making machinery along roads and firebreaks.
The role of birds in dispersal is not known.
Cattle may cause some spread.

Origin and History:

Southern and tropical Africa.
In SA on Kangaroo Island before 1836.
In Tasmania by 1845.
Thought to have been introduced by Afghan camel trains in the 1860's possibly as camel food or as a contaminant.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
All states except Tasmania.

Courtesy Australia's Virtual Herbarium.

Habitats:

Sandy soils. Alluvial soils. Along creek lines.

Climate:

Semi arid regions.

Soil:

Sandy soils. River beds. Alluvial soils.
Prefers bare disturbed soils.

Plant Associations:

Significance:

Camel Melon is the wild form of the Watermelon (C. vulgaris) and Pie Melon.

Beneficial:

Ripe fruits occasionally eaten by sheep and cattle.
Stabilises sandy soils.
Cockatoos, galahs and other birds eat the seeds.
Source of moisture for humans and animals in African deserts.
Fruit and oily seeds have been cooked as food.

Detrimental:

A weed of fallows, firebreaks, roadsides, disturbed ground, pastures and flooded areas.
Often occurs in dense stands causing blockages in tined implements.
Consumes soil moisture reserves.
Relatively unpalatable.
Unpleasant smell when crushed.

Toxicity:

Suspected of being toxic to stock, but rarely a problem in the field.
Causes diarrhoea in humans.

Legislation:

Noxious weed of VIC and WA.

Management and Control:

Very heavy grazing with wethers will control young plants. Hormone herbicides may be used to make the vines more palatable. Atrazine, triclopyr, 2,4-D and metsulfuron with spray oil provide good control.
Control by cultivation, whilst effective, usually increases the risks of wind erosion too much on the sandy soils where most infestations occur.

Thresholds:

Eradication strategies:

Spray with hormone herbicides then graze heavily soon after each germination before the plants become moisture stressed. Early morning spraying is usually the most effective.
Manual removal before flowering is effective on small infestations but requires repeat treatments for many years.
Establishment of perennial pastures such as lucerne can provide good control.

Herbicide resistance:

Biological Control:

Grazing with 24 wethers/ha for 2 weeks on a supplement of 150 g/head/day of Lupins or equivalent provides reasonable control of vegetative plants.

Related plants:

This is the wild form of the Water melon or Pie melon.
Colocynth (C. colocynthis) is very similar but is covered with stiff hairs on the top of the leaves and is perennial.
Watermelon (C. lanatus var. caffer) has much larger, sweet fruit.

Plants of similar appearance:

Prickly Paddymelon (Cucumis myriocarpus) has simple tendrils, smaller leaves that are usually a darker green with fewer lobes, and smaller fruit with soft spines. The cotyledons of Prickly Paddymelon are less obviously veined than those of Camel Melon (Citrullus lanatus).

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P158-159. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P806. Diagrams.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P341-342. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P624-625. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P220.

Gardner, G.A. and Bennetts, H.W. (1956). The toxic plants of Western Australia. (West Australian Newspapers Ltd, Perth). p???.

Gilbey, D. (1989). Identification of weeds in cereal and legume crops. Bulletin 4107. (Western Australian Department of Agriculture , Perth). p???.

Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). p???.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne). p???.

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #320.3.

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). P158. Diagram.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P407-409. Photos.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). p100-101. Diagram. Photos.

Acknowledgments:

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