CALLMANDER, M.W., J. MAZUMDAR & C.E. JARVIS (2019). Typification and nomenclature of the western Indian Ocean islands ferns and lycophytes described in Linnaeus filius's Supplementum plantarum. Candollea 74: 223–234. In English, English abstract.Carl Linnaeus filius (1741–1783) published 16 new species names of ferns and lycophytes in Supplementum plantarum in 1782. Nine of these new taxa originated from the western Indian Ocean islands and were based on collections cited as “Sonnerat per Thouin” or “Thouin” in their protologues. Correspondence between Andre Thouin (1747–1824) and the younger Linnaeus indicates that those new names were based on a set of 50 collections that Thouin shipped to Linnaeus f. in 1779 and were in reality collected by Philibert Commerson (1727–1773) and not Pierre Sonnerat (1748–1814). Original material has been located in Linnaeus filius's herbarium (now in LINN-HS) and duplicates have been located in the Thouin herbarium (now MPU) and in G, P, P-LA and SBT. We formally designate lectotypes for five fern and two lycophyte names described by the younger Linnaeus in Supplementum plantarum: Acrostichum punctatum L. f., Acrostichum viviparum L. f., Adiantum furcatum L. f., Adiantum repens L. f., Lycopodium gnidioides L. f., Lycopodium verticillatum L. f., and Polypodium pica L. f. A lectotype is additionally designated for Asplenium daucifolium Lam., the currently accepted name for Acrostichum viviparum.Received: June 13, 2019; Accepted: November 18, 2019; First published online: December 2, 2019