Euphorbia biformis Watson (1883: 151)

Steinmann, Victor W., 2023, Typification of Mexican Euphorbia (Euphorbiaceae), Phytotaxa 630 (1), pp. 61-68 : 62

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.