Homonyms are names spelling exactly like a name based on a different type that was previously and validly published for a taxon at the same rank (Art. 53.1 of Shenzhen Code). A perpetuation of the use of homonyms can result from original misidentifications which, in turn, are related to lack of the study of the original material. Furthermore, homonyms are valid names (if agree the Arts. 32–45) and they can be re-used to name new taxa at different rank (Art. 55.2). Hence, the study of homonyms is often necessary to avoid disadvantages in Nomenclature and mistakes in Taxonomy. In this paper, the case of Arenaria caespitosa is presented. It was published eight times (from 1790 to 1985) and refer to different taxa (genus to subspecies ranks). Two binomials (referred to Sabulina verna subsp. hercynica) were invalidly published by Ehrhart in 1790 (Arts. 38.1–38.2) and Willkomm in 1863 (Art. 36.1b). The other six names are valid: Salisbury’s A. caespitosa (described in 1796) is illegitimate (Arts. 52.1–52.2) and homotypic with A. balearica; Willdenow’s A. caespitosa (described in 1799 and here lectotypified on LINN-HS816-7-2) is illegitimate (Art. 53.1) and heterotypic with S. verna subsp. hercynica; Vahl’s Arenaria caespitosa [described in 1840 and here lectotypified on C10006116] is currently known as Sagina caespitosa; Philippi’s A. caespitosa (described in 1856 and here neotypified on K000471609) is heterotypic of A. serpens; Muschler’s Arenaria caespitosa (described in 1911 and here neotypified on USM334270) is a heterotypic synonym of A. tetragyna; Kozhevnikov’s Arenaria caespitosa (described in 1985 and here lecotypified on K000723188) is currently known as Thylacospermum caespitosum. Finally, I demonstrated that 1) S. nivalis sensu Nyman is a p.p. synonym of Lange’s S. caespitosa, whereas 2) Reichenbach’s Sabulina caespitosa (here neotypified on the Plate CCVII) is a heterotypic synonym of Sabulina verna subsp. verna.