Seed head of Tragopogon pratensis

Credit: DR JEREMY BURGESS/SCIENCE PHOTO LIBRARY

Caption: Seed head of Goat's beard, Tragopogon pratensis, a member of the Compositae (daisy family). Goat's beard produces a large "clock" of feathery fruits (achenes). This picture looks into the centre of a mature seed head. In the foreground are three "parachutes" attached to stalks ( pale yellow, background ). The parachute is called a pappus, and comprises radial spokes with fine fibrils tangled between them. Each pappus has one stalk, and at the base of the stalk is a single seed. The pappus and seed collectively make up a fruit, the achene. Each achene develops from a single flower within the composite flower head. The pappus itself develops from the outermost layer of the original flower (the calyx). This arrangement allows the wind to detach the dry mature fruits, which may be carried long distances, thus dispersing the seeds.

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Keywords: achene, calyx, compositae, composite flower, fruit, goat's beard, pappus, seed, seed dispersal, tragopogon pratensis, wind dispersal.

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