<i><b>Centaurea aspera</b></i>
<a href="//commons.wikimedia.org/wiki/User:Oceancetaceen" title="User:Oceancetaceen">Oceancetaceen - Alice Chodura</a>
Boswell, J.T. (Ed.), <i>English botany, or, coloured figures of British plants</i>, 3rd Ed., nº 5, pl.710, London, 1878<a rel="nofollow" class="external autonumber" href="https://archive.org/stream/englishbotanyorc05sowe#page/166/mode/2up">[1]</a>