Uncovering Cyperus polystachyos in Europe: Nomenclatural Insights and New Historical Records

<i>Cyperus polystachyos</i> Rottb. is a species primarily distributed across tropical and subtropical regions of the world, while in Europe it remains very rare, with confirmed records only from two Italian sites, i.e., Tor Caldara Natural Regional Reserve (on the southern Lazio coast, central Italy) and Ischia Island (Campania region, southern Italy), where it grows in an open habitat on sulphur-rich soils and in Hungary, along the Danube River (an historical occurrence based on a herbarium collection dated October 1891). Following a detailed examination of specimens preserved in several European herbaria, we identified a previously overlooked historical collection from Sicily, a region where the species had long been considered absent but where this specimen provides the first confirmed evidence of its historical presence. Morphologically, <i>C. polystachyos</i> is highly polymorphic, leading to the description of many taxa over the centuries. Of these, only two varieties are currently accepted, i.e., var. <i>polystachyos</i> and var. <i>holosericeus</i> (Link) C.B.Clarke. To clarify the application of these varietal names, we conducted a nomenclatural study of Rottbøll's <i>C. polystachyos</i> and Link's <i>C. holosericeus</i> Link (the basionym of <i>C. polystachyos</i> var. <i>holosericeus</i>). We designate a specimen housed at C (barcode C10010299), collected by König in India, as the lectotype of <i>C. polystachyos</i> and a specimen deposited at K (barcode K002543977), collected by Drummond in the United States, as the neotype of <i>C. holosericeus</i> (no original material appears to survive for Link's name). For nomenclatural purposes, we also examined the names <i>C. fascicularis</i> Poir. and <i>C. scopellatus</i> Rich., two of the earliest names associated with <i>C. polystachyos</i>. These are lectotypified here on specimens P00644234 (Poiret's collection) and P00254684 (Richard's collection), respectively.