Experts disagree about the number of species in the genus "Attalea" (broadly defined). In 1965, Dutch taxonomist Jan Gerard Wessels Boer estimated that as many as 100 species may be in the genus. In their 1996 "Field Guide to the Palms of the Americas" Andrew Henderson and coauthors recognised 29 species in the genus, while Sidney Glassman recognised 65 species in his 1999 treatment of the group. Largely following Glassman's lead, Rafaël Govaerts and John Dransfield recognised 67 species in their 2005 "World Checklist of Palms". An important element of this disagreement is the decision by Glassman to define species more narrowly than Henderson. As a result, what Henderson interpreted as variation within species, Glassman took as differences between morphologically similar species. This problem is complicated by the fact that many of these species are poorly represented in herbarium collections. The large size of the leaves, inflorescences and fruit of many "Attalea" species makes them difficult to collect. In addition, many important collections, including type specimen, have been lost or destroyed. Sparse or incomplete collections make it difficult to differentiate variation within a single species from variation between different species. Taxonomic uncertainty is exacerbated by frequent hybridisation between species.