Zamia lacandona, a member of the Z. splendens species group, is described from the Selva Lacandona of eastern Chiapas, Mexico. It is distinguished from Zamia splendens Schutzman by its usually single arcuate leaf with falcate leaflets, erect short-peduncled megasporangiate strobili, decumbent microstrobili, and chromosome number of 2n = 16, 17, or 18. When Zamia splendens was described (Schutzman, 1984), collections from the Selva Lacandona of eastern Chiapas were recognized as somewhat more robust and possibly distinct, but were still ascribed to Z. splendens in the publication. During two subsequent botanical expeditions to southern Mexico, one in 1984 by the first author and a second one in 1993 by the second author and Terrence Walters and Charles Hubbuch of Fairchild Tropical Garden, specimens were collected in the vicinity of the Mayan ruins in the Selva Lacandona. Schutzman's (1984) earlier decision to include the eastern populations was conservative, because it was not known at that time whether a continuum in morphological features would bridge the morphological gap or discontinuity between the western and eastern Chiapan populations. Three significant facts clarified the question. First, specimens collected by the first author in the Lacandona forest produced cones for the first time in 1993, demonstrating differences in cone morphology and habit from Z. splendens. Second, plants of Z. splendens almost identical to the type specimen were discovered in nearby Tabasco during the above-mentioned 1993 expedition, extending the distribution range of Z. splendens; this greatly reduced the possibility that a morphological continuum of one large variable species existed. Third, the Lacandona plants have distinct cytological features distinguishing them from Z. splendens. Thus, it was decided that the Lacandona plants are, indeed, worthy of specific status. The large, normally solitary, robust-petioled leaf and relatively small caudex distinguish this species from its congeners in the wild, but in cultivation these features can change and should only be used to distinguish species in conjunction with other characteristics, such as the finely toothed leaflets and cone habit characters (discussed below). Zamia lacandona Schutzman & Vovides, sp. nov. TYPE: Mexico. Chiapas: Selva Lacandona, July 1984 (male pi), Schutzman 517 (holotype, FLAS; isotype, XAL). Figure la-h. Haec species Z. splendenti Schutzman affinis sed apice strobilorum femineorum apiculato, erecto, foliolis novis xerampelinis et non roseis. et dentibus foliolorum tenuibus et non grossis differt. Plants dioecious, 15-60 cm tall. Caudex subterranean, 17—40 cm long, 4.5-8 cm diam. Leaves usually 1, occasionally 2, depending upon condition of the plant and its environment, arcuate, sparingly pubescent upon emergence, 30-100 cm long, 34—80 cm wide; leaflets 7—12 pairs per leaf, opposite to subopposite on a single leaf, linear-lanceolate to slightly oblanceolate, proximal leaflets subfalcate, 13—42 cm long, 1.5—5 cm wide; apex acuminate, equal to unequal; margin subrevolute; marginal teeth in upper half of leaf, 1.0—1.25 mm; base attenuate, reddish brown when expanding, dark green when mature; articulation with rachis dark brown, 5-10 mm wide; petiole semi-terete, dark greenish brown covered with brown tomentum, spinose through approximately % of its length from the base, 20-70 cm long, 10-20 mm diam.; spines terete, 0.8-4 mm long, 0.5-1 mm diam.; petiole base massive and almost encompassing entire apex of caudex, 1.5—3 cm wide; cataphylls chartaceous, elongate triangular, cone cataphylls narrow-triangular, pubescent, 2.8-6.3 cm long, 0.4—1.2 cm wide, leaf cataphylls deltoid with aristate apex, 2.2—3.4 cm long, base 2.3—3.8 cm wide. MicrospoNOVON 8: 441-446. 1998.