[1] As a young man he assisted botanist Auguste de Saint-Hilaire (1779–1853) with studies of Brazilian flora.

His microscopic investigation of fungi, particularly parasitic species, contributed much to the understanding on the complexities of their nature and development.

It was in this work he introduced the term pycnidium to describe the asexual fruiting body found in many species of fungi.

He is credited with providing classification taxa for the following genera: Crucibulum, Glomus, Sebacina, Terfezia, Tilletia and Hypomyces (the latter genus with Elias Magnus Fries).

Some of his best work was done in collaboration with his brother, Charles Tulasne (1816–1884), such as "Fungi hypogaei" (1851) and the three-volume "Selecta fungorum carpologia" (1861–65).