Cockleburs
What are they?
This is a small group of plants in the daisy family (Asteraceae), although the rather small and underwhelming flowers may not make this immediately apparent. However, a closer inspection of a 'flower' will reveal that it consists of a tight collection of tiny florets, surounded by an outer layer of small, overlapping bracts. Thus, the flowers are very like those of daisies, but without the outer ring of showy petals. The cockleburs are largely plants of warm-temperate to tropical regions and are not native to the UK. However, their hooked seed capsules have a way of finding their way into all sorts of products that are transported around the world (woollen materials and various grains are typical examples) and they regularly turn up throughout the developed world, though may often prove to be climate-intolerant and thus do not last for long.
Where are they found?
As introduced plants, cockleburs are most likely to be found in human-influenced habitats. In the past, they have been weeds originating from spilt grain at docks or as constituents of imported fertiliser products. Such sources rarely occur these days and it is more likely that any occurences might come from birdseed impurities.
Identification
The two species of cocklebur that have been recorded in our area are distinctly different from each other in their leaves and their overall appearance. Spiny Cocklebur is eaily told at any size by its yellowish spines and dark leaves with pale mid-veins. Rough Cocklebur is annoyingly non-descript and there are actually several, rather similar, species to consider which could theoretically show up. It has something of the look of a mallow about it, due to the broad leaves, but the leaves have a very rough, sandpaper-like feel to them and, if in fruit, the hooked seed capsules are distinctive.
Rough Cocklebur Xanthium strumarium
Introduced, probably from southern Europe but perhaps also from further afield. Rare, as a casual probably in imported seed mixes and not surviving for long. Flowers July to October. A branching annual which may grow to a metre in height but is often much smaller. A very variable species in the shape of its leaves, which are broad and variously toothed or lobed. The leaves are distinct in their very rough surfaces which can feel like sandpaper to the touch.
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Spiny Cocklebur Xanthium spinosum
Introduced, probably from southern Europe. Rare, as a casual probably in imported seed mixes and not surviving for long. Flowers July to October. A branching annual which may grow to 80cm in height but is often much smaller. The yellowish stem spines and dark green leaves with pale midribs are distinctive. If plants reach maturity, the hooked seed capsules are very distinctive late in the year.
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