linguistic:paraphrasing
Taxonomy

There are about 30 to 40 species of Ulmus (elm); the ambiguity in number results from difficulty in delineating species, owing to the ease of hybridization between them and the development of local seed-sterile vegetatively propagated microspecies in some areas, mainly in the Ulmus field elm (Ulmus minor) group. Oliver Rackham describes Ulmus as the most critical genus in the entire British flora, adding that 'species and varieties are a distinction in the human mind rather than a measured degree of genetic variation'. Eight species are endemic to North America and three to Europe, but the greatest diversity is in Asia with approximately two dozen species. The oldest fossils of Ulmus are leaves dating Paleocene, found across the Northern Hemisphere.

The classification adopted in the List of elm species is largely based on that established by Brummitt. A large number of synonyms have accumulated over the last three centuries; their currently accepted names can be found in the list of Elm synonyms and accepted names.

Botanists who study elms and argue over elm identification and classification are called "pteleologists", from the Greek πτελέα (elm).

As part of the suborder urticalean rosids, they are distantly related to cannabis, mulberries, figs, hops, and nettles.