Typification of Mexican Euphorbia (Euphorbiaceae) Author Steinmann, Victor W. 0000-0003-0103-9575 Instituto de Ecología, A. C., Centro Regional del Bajío, Av. Lázaro Cárdenas 253, 61600 Pátzcuaro, Michoacán, Mexico. steinmav@gmail.com text Phytotaxa 2023 2023-12-12 630 1 61 68 https://phytotaxa.mapress.com/pt/article/download/phytotaxa.630.1.5/51357 journal article 10.11646/phytotaxa.630.1.5 1179-3163 10361687 Euphorbia biformis Watson (1883: 151) ≡ Zygophyllidium biforme (Watson) Arthur (1911: 260) . Lectotype (designated here):— MEXICO . San Luis Potosí : in the San Miguelito Mountains , 1876, J.G. Schaffner 860 (GH barcode 00032859 !; isolectotypes K barcode K000253763 !, PH no. 0933919 /barcode 00013408 photo!). Euphorbia biformis was described by Serrano Watson using three collections from the San Miguelito Mountains of San Luis Potosí , Mexico : Schaffner 860 , Schaffner 862 , and Parry & Palmer 806 . Various authors have treated Euphorbia biformis as a synonym of Euphorbia macropus , e.g., Huft (1979) , Steinmann & Felger (1997) , and Calderón de Rzedowski (2001) . Interestingly, only two of the collections cited by Watson belong to E. macropus , and the Parry and Palmer gathering is in fact Euphorbia graminea Jacquin (1763: 151) . Because the Schaffner specimens most closely correspond to the morphological description prepared by Watson (e.g., “from a tuberous root”), Schaffner 860 at GH is designated as the lectotype . It is the most complete specimen. It was labeled as the “TYPE” by Louis C. Wheeler in 1939 and as the “ LECTOTYPE ” by Rogers McVaugh in 1993 and also by Mark. H. Mayfield in 1994. However, a formal lectotypification had not been done until now.