The indigo milk cap (Lactarius indigo) is edible mushroom. Like the rest of the genus Lactarius it exudes fluid (called 'milk' or 'latex'). The liquid of this particular mushroom is blue. The indigo milk cap grows in Eastern North America, East Asia and in Europe is found in Southern France.
I couldn't resist the temptation to add the indigo milk cap to my Voynich manuscript plant id list as possibility for the mushroom on fol. 99v (per Beinecke library). The VMs fungi also appears to be squirting something blue.