Synopsis of Euphorbia subgen. Esula sect. Helioscopia (Euphorbiaceae) in Iran with the description of Euphorbia mazandaranica sp nov.

Euphorbia subgen. Esula with about 480 species is one of the most diverse and complex lineages of the giant genus Euphorbia. Species of this subgenus are usually herbaceous and are mainly distributed in temperate areas of the Northern Hemisphere. Th is paper updates the taxonomy and distribution of Euphorbia (subgen. Esula) sect. Helioscopia in Iran since the publication of 'Flora Iranica' in 1964. We provide a key, species descriptions, illustrations (for most species), distribution maps, brief characterization of ecology as well as relevant notes for the 12 species of this section occurring in Iran. As a result of this revision, E. altissima var. altissima is reported as new for the country, and a new species from northern Iran, Euphorbia mazandaranica, is described and illustrated. With the exception of E. helioscopia, a widespread weed in temperate regions worldwide, the remaining species occur in the Alborz, Zagros and northwestern regions of Iran.