Polypodium acutum Burm. f., Fl. Ind.: 232. 1768.

Lectotypus (designated here): SRI LANKA: sine loco, s.d., Hermann s.n. (BIF-CEYL p. 152, upper specimen) (Fig. 3).

= Osmunda regalis L., Sp. Pl.: 1065. 1753.

Notes. – No original material of Polypodium acutum has been located in G-PREL. BURMAN (1768) referred only to three pre-Linnaean polynomial names and an illustration (PLUKENET, 1694: tab. 285, fig. 1). One of these polynomial names referred to Burman’s father work: “ Burm. Zeyl. 98 ”. Johannes Burman’s Thesaurus zeylanicus, published in 1737, was based mainly on a Paul Hermann herbarium from Ceylon. This herbarium is bound in a folio volume now kept in BIF-CEYL with Benjamin Delessert’s personal library (see LOURTEIG, 1966). Page 152 of this bound herbarium features a collection of Polypodium acutum, bearing a reference to the protologue as well as the name of the new species, both from N.L. Burman’s hand. This collection, representing original material, is here designated as lectotype (Fig. 3).

The lectotype matches with sterile pinnae of the fern Osmunda regalis, showing similar shape of pinnules and free venation. This species is widely cultivated and popularly known as ‘royal fern’. It does not occur naturally in Sri Lanka (SLEDGE, 1981) and Hermann probably collected a cultivated plant.