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Background and Aims: Polycarpon is a genus traditionally comprising about 16 species distributed in tropical and temperate regions. Molecular studies demonstrated its polyphyly, highlighting three supported clades: the P. coquimbense-suffruticosum aggregate (from South America), P. prostratum (tropical), and the P. tetraphyllum aggregate (mainly in the Mediterranean region). The first two clades have been excluded from Polycarpon: P. coquimbense, P. suffruticosum, and P. anomalum recently transferred to Augustea, and P. prostratum recognized under Polycarpaea. The remaining members represent a polyploid complex treated as a single species, P. tetraphyllum. Taxonomic questions remain open, especially concerning the number of taxa occurring in some geographical areas. Among them is South America, for which we here present a synopsis.Methods: This work is based on field surveys, examination of specimens, and analysis of literature. The International Code of Nomenclature for Algae, Fungi and Plants was consulted.Key results: Three subspecies of Polycarpon tetraphyllum are recognized in South America: subsp. apurense (from Argentina, Colombia, Paraguay, and Venezuela), subsp. tetraphyllum (alien in most of the countries), and subsp. peruvianum (endemic to Peru). The latter subspecies is newly described here and it differs from subsp. diphyllum and subsp. tetraphyllum by stipule shape, leaf arrangement and colour, arrangement of flowers in inflorescences, petal length, and stamen number. It also presents a distinct habitat: dry, rocky soils, in contrast to the sandy soils or disturbed areas where other subspecies grow. The name P. urbanianum, previously considered as a Peruvian endemic, is here demonstrated to be not a species of Polycarpon. A diagnostic key of the South American subspecies of P. tetraphyllum is proposed.Conclusions: The results obtained remark the variability of Polycarpon tetraphyllum s.l. and highlight that the flora of South America, especially concerning the small Caryophyllaceae needs to be further investigated. 

The namesArenaria mattfeldii,A. pallens,A. peruviana,A. pintaudii, andA. stuebelii(Caryophyllaceae, Arenarieae) from Peru and Bolivia were studied and neotypified based on specimens preserved at B and P. 

All the names in Paronychia described from South America are investigated. Five names (P. arbuscula, P. brasiliana subsp. brasiliana var. pubescens, P. coquimbensis, P. hieronymi, and P. mandoniana) are lecto- or neotypified on specimens preserved at GOET, K, LP, and P. The typification of nine names, first proposed by Chaudhri in 1968 as the “holotype” are corrected according to Art. 9.10 of ICN. Three second-step typifications (Art. 9.17 of ICN) are proposed for P. camphorosmoides, P. communis, and P. hartwegiana. The following nomenclatural changes are proposed: P. arequipensis comb. et stat. nov. (basionym: P. microphylla subsp. microphylla var. arequepensis), P. compacta nom. nov. pro P. andina (Philippi non Gray; Art. 53.1 of ICN), P. jujuyensis comb. et stat. nov. (basionym: P. hieronymi subsp. hieronymi var. jujuyensis), P. compacta subsp. boliviana comb. nov. (basionym: P. andina subsp. boliviana), and P. compacta subsp. purpurea comb. nov. (basionym: P. andina subsp. purpurea). A new species (P. glabra sp. nov.) is proposed based on our examination of live plants and herbarium specimens. P. johnstonii subsp. johnstonii var. scabrida is synonymized (syn. nov.) with P. johnstonii. Finally, P. argyrocoma subsp. argyrocoma is excluded from South America since it was based on misidentified specimens (deposited at MO) of P. andina subsp. andina. A total of 30 species (43 taxa including subspecies, varieties, subvarieties, and forms) are recognized, highlighting that for some (Paronychia chilensis, P. communis, P. setigera) we provisionally accept Chaudhri’s infraspecific classification, since the high phenotypic variability of these taxa is quite complicated and further investigations need to solve their taxonomy.