Two prickly customers

January 19th 2018

I should clarify at the outset that the ‘Two prickly customers’ does not refer to this article’s contributors!

Having cleared that up I can safely continue – these images of the dead fruiting heads of composites were taken recently by David Haines, as part of early trials in ‘stacking’ digital images.

On the left is spear thistle Cirsium vulgare (constructed from seven images) from Culkein Drumbeg (NC1133), while on the right is burdock Arctium minus (constructed from thirteen images) from the side of Loch Drumbeg (NC1132).  Both bear rigid spiny involucral bracts which dissuade animals from grazing the heads before the fruits can be dispersed, but there the similarities between the two end.

The fruits of spear thistle, like those of many composites, have feathery pappus hairs sprouting from the top of the ovary.  These hairs spread, when the fruits are ripe and the air is dry, forming rigid parachutes and the means by which they are wind-dispersed, the well-known thistledown.

Those of burdock also bear pappus hairs, but they are short and cannot function as parachutes.  So seed dispersal in the case of  burdock is by the hooked bracts catching in the fur of passing animals, the whole head, or burr, is detached and the hard black fruits are gradually shaken out as the bearer travels further afield.

Both plants are usually found in disturbed ground and neglected gardens in Assynt, occasionally way up in the hills, but spear thistle is much more widespread.  Burdock is a tap-rooted perennial that persists where it gets a foothold; spear thistle is a biennial, which just produces one set of flowers and fruits; contrasting strategies for life.

Of course it should be noted that their defences do not protect either from the predations of birds, in particular goldfinches.

Ian M. Evans

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Recent Sightings

Kestrel

Single bird hovering between road and waterfall, Clashnessie (Neil McCrimmon) (26/11)

Fieldfare and Redwing

A mixed flock of c30 fieldfare and c10 redwing in tall aspens, Nedd (Ian Evans). Mixed flock of 200+ birds over Culkein Drumbeg (DAH) (23/11)

Dipper

Single bird by River Inver, Brackloch (Carol Langford) (22/11)

Pheasant

Single hen bird in back garden, Nedd (Ian Evans).  Rarely seen in this part of Assynt (21/11)

Great Northern Diver

Single bird, Bay of Stoer (John Gilbertson) (21/11)

Redwing and Fieldfare

c80 birds in a mixed flock flying over the B869 by Rhicarn (Richard Chappell and Ennis Jones) (20/11)

Dipper

Single bird in tree overhanging river Inver, Little Assynt (Richard Chappell and Ennis Jones) (20/11)

Kestrel

Single bird hovering by roadside, Inchnadamph (Richard Chappell and Ennis Jones) (20/11)

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