Bur parsley (Caucalis sp.): entire flowering and fruiting plant with separate flower, fruit and seed. Coloured engraving after F. von Scheidl, 1772. | Wellcome Collection
How burs disperse seeds in fall
The weedy-seedy plants of fall - MSU Extension
Bur clover (Medicago polymorpha) | Feedipedia
Wildflower Pirri-pirri-bur Irish Wild Flora Wildflowers of Ireland