thistle rennet

En: "Vegetarian cheeses are made with rennets of non-animal origin. In the past, fig leaves, melon, wild thistle and safflower have all supplied plant rennets for cheese making. However, most widely available vegetarian cheeses are made using rennet produced by fermentation of the fungus Mucor miehei. Vegetarian cheese may also be made using a rennet from the bacteria Bacillus subtilis or Bacillus prodigiosum.
Advances in genetic engineering techniques mean that some vegetarian cheeses may now be made using chymosin produced by genetically engineered micro-organisms. ..."

Source: Information Sheet of the Vegetarian Society "Cheese and Rennet" http://www.vegsoc.org/info/cheese.html

NB: In Portugal, you can find an astonishing variety of thistle rennet cheese (cardo cheese) in supermarkets. Also, a lot of people grow and use their own cardo.