Morphological variation between the two species of the palm genus Gaussia (Arecaceae) from Mesoamerica

Palms (Arecaceae) represent a challenge for studies of morphological variation for several various reasons. For instance, the height of many species makes them difficult to collect, and in some cases, the size of the leaves or the presence of spines make them hard to process and preserve in herbaria. Arecaceae is one of the most diverse families of monocots (ca 2600 species), and many of its species remain poorly studied. The genus Gaussia has five recognized species. Their distributions are restricted to Central America and the Caribbean islands, and for most of them, their taxonomic descriptions are the only information available. Two species - Gaussia maya and G. gomez-pompae - are exclusively distributed in Mesoamerica. They occur allopatrically and their populations are isolated from each other. The aim of this work was to evaluate the levels of intra- and inter-population morphological variation in both species and determine the possible factors that influence such a variation. We examined the morphological variation of 13 vegetative structures of 155 adult individuals from nine populations of G. maya and G. gomez-pompae. The differentiation among populations was significant for almost all the variables and was consistent with an isolation-by-distance pattern. A linear discriminant analysis, Mahalanobis distances and UPGMA cluster analysis based on Euclidean distances among populations showed that three morphological groups could be distinguished. One group contained only individuals of G. maya, the second only G. gomez-pompae, while the third group represents a yet unknown taxon. Pairwise differentiation tests clarified the morphological distinction among the three groups. This work highlights the importance of quantifying morphological variation between populations of little-studied palms.