Caltrop is a flat, sprawling, summer-growing, annual herb. Stems. Caltrop has numerous green to reddish brown stems radiating from a crown. It grows prostrate to 2 m long with many branches and fine hairs.
As A Soil Indicator:
Low Calcium, Very Low Potassium, High Phosphorous, High Magnesium, High Iron, High Aluminum  Very little organic matter, Anaerobic bacteria, Occurs on a wide range of soils. More abundant on sandy soils..
Life cycle: 
Annual or short lived perennial. Seed germinates from spring to autumn after rain and it grows rapidly producing deep roots. It grows mainly in the warmer months. It grows profusely after summer rains and flowers mainly in summer and autumn. The flowers open in the morning and close or drop their petals in the afternoon. They usually die in autumn or winter after the first frosts. In tropical areas the deep taproot develops and the plant becomes a perennial.
Nectary plant. Fodder. Kills bacteria and used in herbal medicine as a diuretic, tonic and aphrodisiac.
Injures animal feet. Contaminates wool. Contaminates dried fruit. Injures shearers and wool, fruit and vegetables handlers.
Dense infestations may be toxic to stock causing photo sensitisation of skin around lips, ears and eyes followed by swelling of the head. Sheep are more commonly affected than cattle.
Causes a chronic staggers mainly in the British breeds of sheep.
Spiny burr may cause injury to feet and intestines of stock and form pussy sores where they penetrate the frog of horses hooves.
It can accumulate nitrate and oxalate levels high enough to cause nitrate poisoning and oxalate poisoning in stock especially after spraying with industrial chemical herbicides.

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