Giovanni Battista de Toni (2 January 1864, Venice – 31 July 1924, Modena) was an Italian botanist, mycologist and phycologist.

In 1885 he graduated from the University of Padua, where he studied natural sciences and chemistry with Pier Andrea Saccardo (1845-1920) and Francesco Filippuzzi (1824-1886).

[1] During his career, he took numerous scientific trips throughout Europe — travels where he met and studied with scientists that included Jacob Georg Agardh (1813-1901), Alfred Mathieu Giard (1846-1908), Louis Mangin (1852-1937) and Narcisse Théophile Patouillard (1854-1926).

He issued the exsiccata work Phycotheca Italica, collezione di alghe Italiane (1886-1889, with David Levi as co-editor) and the series Herbarium Phycologicum, collab.

[3] In 1889 he began work on "Sylloge algarum omnium hucusque cognitarum", a massive project that was an index of all known algae.