Euphorbia potosina Fernald (1901: 495) .

≡ Chamaesyce potosina (Fernald) Arthur (1911: 260) .

Lectotype (designated here):— MEXICO. Tamaulipas: near Tula, 21 September 1898, E.W.D. Holway 3200 (GH, mounted on two sheets, barcode 00012500! and barcode 00011318!; isolectotype F no. 196531).

Three collections were cited in the original description: Schaffner 856 (in part), Parry & Palmer 814 (in part), and Holway 3200. All of these are at the Gray Herbarium of Harvard University (GH), where Fernald worked. The Holway collection is mounted on two sheets, clearly labeled as “Sheet 1 of 2” and “Sheet 2 of 2.” These later received separate barcodes: 00012500 and 00011318, respectively. The former bears an annotation label by Rogers McVaugh in 1993 as “ lectotype, GH sheet 11318 is an isolectotype.” These are here both treated as part the lectotype since according to Turland et al. (2018), Art. 8.3, “a specimen may be mounted as more than one preparation, as long as the parts are clearly labelled as being part of that same specimen…”.