Cathead
 Cathead

Cathead biology
Tribulus terrestris
Family: Zygophyllaceae.

Common names: Cathead, Bindyi, Bullhead, Bull’s head, Burnut, Caltrop, Cat’s head, Devil’s thorn, Goathead, Goat head burr, Goat’s head, Puncture vine.

Confused with: Yellow vine (T. micrococcus). There has been some confusion between yellow vine and cat-head, and different varieties within yellow vine itself. The species can be distinguished by:

* Leaves – yellow vine’s leaflets are bright green, 6 - 13 mm long and 3 - 5 mm wide, where as cat-head’s are a bluish/grey colour generally 4 – 8 mm long and 2 – 4 mm wide.

* Flowers - yellow vine has open, bright yellow flowers with petals 6 – 13 mm in length, where as cat-head’s flowers are normally not prominently open, with petals 3 – 6 mm long.

* Seed head – the yellow vine seed and seed head is spineless, or nearly so, where as cat-head seeds each have 4 robust spines, 2 spines that spread near the tip, 3 – 8 mm long, and 2 shorter spines at the base, 1 – 4 mm long.

Description:

Seedling leaves - the cotyledon leaves are oval-shaped with a flattened tip, 8 mm long and 4.5 mm wide and borne on stalks 1 – 2 mm long. They have a prominent, indented, central mid-rib. The 1st and 2nd true leaves have 2 and 3 pairs of leaflets, respectively. The number of leaflets increases on later leaves. The early leaflets are mid to dark green, shiny and have obvious hairs on their margins.

Leaves – have 4 – 8 pairs of elongated oval-shaped leaflets, 4 – 10 mm long, 2 – 4 mm wide and have short stalks or no stalk at all. The leaflet pairs are not equal in length. The upper leaflet surface is green to greyish/blue. The lower leaf surface is paler and also hairy giving the surface a silvery appearance. The leaves are borne opposite each other on the stem.

Plants – the young stems and leaves are covered in long silky hairs. Plants have a prostrate growth habit with the adult stems much branched, purple/brown to red/brown in colouration, and to 2 m in length. The weed often forms mats and radiates out from a deep woody taproot that extends to 2.6 metres in depth and has a number of fibrous lateral roots.

Flowers – occur singly and have 5 yellow petals, 3 - 6 mm long. The flower diameter ranges from 6.5 – 12 mm. These flowers are borne in the leaf fork of the smaller leaf in the leaflet pair and last only one day.

Seeds - the mature seed head is a star-shaped, woody, brown to red burr, 6 – 15 mm in diameter, with 5 wedge-shaped woody segments. Each segment has 4 hard spines, 2 spines that spread near the tip, 3 – 8 mm long, and 2 shorter spines at the base, 1 – 4 mm long. The seeds are yellow, oval-shaped, 2 – 5 mm long. There are 2 to 4 seeds in each segment, or up to 20 per burr.

Lifecycle/Biology: An annual or biennial plant that germinates after rainfall in late spring and summer, from the soil surface, or from up to 5 cm in depth in lighter soils. Plant growth is rapid and a deep root system is produced in a few weeks. The first flowers may be formed when the plant is only 3 weeks old and the first seed heads are produced in the first 5 to 6 weeks, with between 100 and 500 seed heads produced by a mature plant. Flower production continues for several months during summer and autumn, until the plants are frosted off and die in autumn and winter. Very few seeds germinate after shedding, but by six months dormancy has disappeared. The woody covering protects the seeds and allows buried seed to remain viable for many years. The plant can regrow from the taproot and in more tropical areas may reshoot from the taproot in the following season. The burr segments are easily dispersed as they stick to the rubber tyres, shoes etc.

Ecology: A weed of cultivation, degraded pastures, roadsides, irrigation channels and areas bared by mechanical disturbance. It is well adapted to all soil types, growing particularly well on lighter soils.

The problem: A common but troublesome weed to control on irrigation structures and rotabucks, and in many cultivated crops, particularly on recently developed fields. Control of this weed is difficult to achieve through cultivation alone because of successive germination events and the ability of the plant to reshoot from the taproot. The hard spines can puncture tyres and cause physical injury.

Distribution: Common in all mainland States of Australia.

Origin: A cosmopolitan weed originating in the Mediterranean region. 

References:

Plants of Western New South Wales, p. 438.

Crop Weeds of Northern Australia, p. 74.



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