Two New Species of Zamia (Zamiaceae, Cycadales) from Southern Mexico

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Abstract
Two new species of the genus Zamia (Zamiaceae, Cycadales) from southern Mexico are described. Zamia sofonuscensis, an arborescent species from the state of Chiapas, seems most closely related to Z. inermis. Zamia cremnophila, a cliff-dwelling, pendent-leaved species from Tabasco, appears to belong to a species group including Z. purpurea and Z. splendens. We have endeavored to utilize an Adansonian approach to species delimitation in Zamia by employing as many characteristics as possible. Our concept of species is compared to the extremes of fine splitting and extreme lumping of taxa used in the past. Both new species exhibit relatively symmetrical karyotypes with a diploid chromosome number of 16; Z. cremnophila has a symmetry index of 1.65, and that of Z. soconuscensis is 2.08. The species of Zamia thus far studied appear to support the hypothesis that asymmetrical, high-numbered karyotypes, concomitant with reduced vegetative and reproductive structures, are common in inhospitable environments, but discrepancies exist.