A Close-up View of the Canadian Thistle
- Photographic study by Brian Johnston of the creeping thistle, Cirsium arvense, with many fine images, both macroscopic and microscopic.
- http://www.microscopy-uk.org.uk/mag/artaug06/bj-CanThistle.html

A Close-up View of Two Thistles
- Photographic study by Brian Johnston of Cirsium vulgare and Carduus nutans, with fine images of flowers, stems and prickles.
- http://www.microscopy-uk.org.uk/mag/artjun04/bjthistle.html

Cirsium arvense
- Several photographs of the Creeping Thistle and some identifying features.
- http://www.plant-identification.co.uk/skye/compositae/cirsium-arvense.htm

Cirsium palustre
- Two photographs and a description of the Marsh Thistle.
- http://www.plant-identification.co.uk/skye/compositae/cirsium-palustre.htm

Cirsium heterophyllum
- Several photographs of the Melancholy Thistle and some identifying features.
- http://www.plant-identification.co.uk/skye/compositae/cirsium-helenioides.htm

Cirsium vulgare
- Photographs and description of the Spear Thistle, including one in its natural habitat on the Isle of Skye.
- http://www.plant-identification.co.uk/skye/compositae/cirsium-vulgare.htm