Abstract
The genus Zamia is morphologically and ecologically the most diverse of the order Cycadales. Throughout its history this genus has been restricted to the New World and is presently almost entirely restricted to the Neotropics. Unusual anatomical traits of the leaflets, such as the sunken stomata and thick cuticle, are common in this and related genera. The objective of this research was to study and compare the leaflet anatomy of Zamia acuminata and Z. pseudomonticola and establish possible phylogenetic relationships between the anatomical traits and the near relatives of these species. The leaf material was obtained from living plants and then processed for electron microscopy study. We found that both species are very similar to each other and to Z. fairchildiana, and that they share several unusual traits with other species of the genus, such as the parenchyma morphology, the spatial distribution of tissues between the veins and the stomata morphology. The main differences between these species were seen in their fiber clusters and in the abundance of trichome basal cells on the epidermis. The anatomical similarities between the three species could be the result of their close phylogenetic relationship and the divergences between them could be the result of recent speciation during the Pleistocene, resulting from geological changes in Southern Costa Rica.
Highlights
Z. pseudomonticola is known from Eastern Puntarenas Province, Costa Rica, and Western Chiriquí Province, Panama; this species grows in wet and rain forests between 1 000 and 1 600m altitude in both countries and it is one of the few Central American species of Zamia that could be considered montane
As with other Zamia species, Z. acuminata and Z. pseudomonticola leaflets show an arrangement of traits for very different environments (Greguss 1968, Acuña-Castillo & Marín-Méndez 2012)
Some aspects of the leaflet anatomy are shared by all three species, such as the scarcity of trichome basal cells on mature leaflets, the presence of a rectangular- to wedge-shaped adaxial fiber bundle, and the relatively small abaxial fiber bundle
Summary
The internal anatomy of the petiole-rachis axis is characterized by the dominance of parenchyma along with some mucilage ducts and relatively few and small discreet vascular strands which, in cross section, show an omega (Ω) shape arrangement This trait is diagnostic of the order (Norstog & Nicholls 1998). Stevenson (1981, 1990), Stevenson et al (1996) and Norstog & Nicholls (1998) provide general descriptions of several aspects of the leaf anatomy of diverse cycad genera In other genera, such as Cycas, the differences in the arrangement, abundance and distribution of the tissues inside the leaflets are used to clarify the taxonomy of some confusing species groups (Hill 1996). Stev. have demonstrated that even though the foliar anatomy follows a general pattern, there are details in which the species differ, such as the shape and distribution of fiber bundles associated with the vascular tissue, and the size and shape of the air chambers of the mesophyll (Acuña-Castillo & Marín-Méndez 2012)
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