Burdocks
What are they?
These rather impressive plants are members of the Asteraceae, having the compound flower clusters of small florets that are typical of the family. Burdocks often grow to around two metres in height, with long, arching branches carrying clusters of spiny flowerheads and with large, dock-like or rhubarb-like leaves.
Where are they found?
Burdocks are mostly plants of shady places on heavier soils, especially in areas prone to being wet over winter. The hooked seedheads latch onto the fur of animals for their distribution and can become common along shady footpaths where dogs are readily walked.
Identification
'Classic' examples of burdock species can be identified with careful attention to the distinguishing features, but there appears to be much variation in populations of these plants and they are known to hybridise with each other. It is also likely that the current understanding of the taxonomy for these plants is incorrect and there is much confusion as to the true status of the subspecies pubens of Lesser Burdock, which may be better recognised as a species that originated as a hybrid between two other taxa. Lesser and Greater Burdock are fairly easy to tell apart by looking at the position of the flowerheads on their branches and by checking the centre of a leaf petiole of a basal leaf (useful if the plant is not in flower). Measurements of flower parts may be required for further identification of subspecies, as well as careful study of the hairs on the flowerheads.
Lesser Burdock Arctium minus
Native. Common and widespread throughout the region on most soils and typically the species found in disturbed habitats around farms, industrial buildings and associated rough ground. Flowers July to September. Petioles (stalks) of the basal leaves are hollow inside and usually not strongly grooved on the upper side. The flowerheads have short stalks and are thus arranged in a spike-like way rather than forming flattened heads. Phyllaries hairless or nearly so in the subspecies minus but densely webbed with hairs in subspecies pubens. Typically, pubens has longer flower stalks than minus, but many plants are intermediate and difficult to assign to subspecies.
In the photos below, the first row shows subspecies minus while the second row is typical of subspecies pubens.
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Greater Burdock Arctium lappa
Probably a neolithic introduction from mainland Europe. Perhaps more closely tied to damp woodland and the margins of water courses than the other burdocks and typically found on heavier, clayey soils. Flowers July to September. Petioles (stalks) of the basal leaves are solid inside and usually strongly grooved on the upper side. The flowerheads form more or less flat-topped clusters, as the lower flowerheads have longer stalks that bring them closer to the level of the uppermost flowerheads. Phyllaries hairless or more or less so.
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Woolly Burdock Arctium tomentosum
Introduced from mainland Europe. A rare casual which doesn't seem to persist. Because of identification problems, the status of this plant in gthe region remains unclear, but it is worth keeping an eye out for. Flowers July to September. Petioles (stalks) of the basal leaves are solid inside. The lower flowerheads have long stalks but don't form flat-topped clusters with the upper flowerheads. Phyllaries densely hairy like spider webbing and very pale in appearance.
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