AwesomeUsername wrote:Psilocybes turn blueish under the cap when you pick them, that's what makes them unique and recognizable.
Actually, not all do. Psilocybe Semilanceata doesn't blue very strongly. To make it even more confusing, some non-psilocybes also blue, like Conocybe Cyanopus. That one does contain psilocin (though I couldn't say if it is otherwise free from mycotoxins and safe to eat). Several Boletus species also bruise blue, but do not contain psilocin.
A very common characteristic of psilocybe mushrooms is their translucent gelatinous outer layer of the cap when young and wet. Older or partially dried caps do not show this feature anymore, so it is not a really good feature for discrimination in the field. It is the name-giving feature of the psilocybe mushrooms, psilo cybe means "bald head" in classical Greek.
The safest test for an amateur to determine if a freshly picked wild mushroom is a psilocybe, is to make a spore print. Psilocybe mushrooms give dark purple spore prints.
If you are not a seasoned picker, it is very easy to make mistakes. Don't ingest any finds until you are certain of your determination skills. Only collect to make prints and compare with pictures in books and on the internet. Learn from this until you are certain to have mastered the required skills.
If you must have psilocybe mushrooms for ingestion and lack the necessary determination skills, simply grow some at home. It is not very hard and quite satisfying.