Cynorkis citrata is the correct name for Cynorkis citrina (Orchidaceae, Orchidoideae)

In a recent correspondence in this journal, Cynorkis citrina Bytebier & Pailler (2019: 299) was proposed as a new combination based on the assumption that Habenaria citrina Du Petit-Thouars (1822: tab 16) was its earliest name and thus its basionym. The latter combination was established by Du Petit-Thouars in his seminal work “Histoire particulière des plantes Orchidées recueillies sur les trois îles australes d’Afrique, de France, de Bourbon et de Madagascar”, in which 91 orchid species are illustrated. The protologue of Habenaria citrina consists only of an illustration with analysis (Fig. 1) and a short description in the accompanying tables for genera and species. However, it has been pointed out (Friis & Rasmussen 1975, Stafleu & Cowan 1976) that prior to the publication of his book “Histoire particulière”, Du Petit-Thouars already offered a “Cahier” of six grand folio coloured paintings that also appear in “Histoire particulière” for sale. Friis & Rasmussen (1975) showed that this “Cahier”, which is extremely rare and of which they could only locate two copies, must have been released sometime between 1804 and 1819, although the exact date is not known. Plate V (Fig. 2) in the “Cahier” depicts the same taxon as tab. 16 in “Histoire particulière”, but is there named Habenaria citrata. It appears as though Du Petit-Thouars consciously wanted to change the epithet from “citrata”, meaning “steeped in lemon juice” to “citrina”, meaning “lemon yellow” and most likely referring to the colour of the flowers. Despite the fact that Rasmussen (1979), already back in 1979, pointed out that the name Habenaria citrata precedes the name Habenaria citrina, the former name remained absent from databases such as IPNI (http://www.ipni.org), Tropicos (http://www.tropicos.org) and WCSP (https://wcsp.science.kew.org), and escaped our attention. This oversight is corrected below, and a taxonomic treatment is presented in which all homotypic synonyms are listed.