Euphorbia marciae: A New Species from the Balsas Depression of Mexico

Euphorbia marciae, a new species from the lowlands of the Balsas Depression in southwestern Mexico, is described and illustrated. The species was first collected by the renowned botanist George B. Hinton during his explorations of the area in the 1930s. It is known from only five collections made in northwestern Guerrero and the extreme southwestern portion of the state of M & eacute;xico, at elevations from 250 to 610 m. Vegetation of the area is tropical deciduous forest. Euphorbia marciae belongs to Euphorbia subg. Chamaesyce sect. Anisophyllum and resembles E. apatzingana, E. hyssopifolia, and E. nutans. However, it differs from these species in having smooth seeds. The seeds are nearly identical to those of E. pionosperma, an endemic species occurring in the Sierra Madre Occidental of eastern Sonora and western Chihuahua. However, the leaves of E. pionosperma are more conspicuously serrate and have larger stipules. In addition, Euphorbia pionosperma has smaller involucres and involucral appendages. Following IUCN Redlist criteria, E. marciae should be treated as Data Deficient (DD) until the species can be relocated and its populations field evaluated.