This species is widespread across eastern and central North America, especially on seasonally damp, fertile soils; it is tolerant of eutrophic conditions (e.g. Belt 2015). Although much reduced by Dutch Elm Disease, mature trees are still scattered across Ky., with locally abundant regeneration from seed. Also, several cultivars and hybrids with some resistance are now widely available. U. americana, broadly defined, varies greatly in leaf size, shape and pubescence, and there has been much misidentification of vegetative material; see notes under other species. A curious feature of seedlings is the frequent occurrence of opposite leaves above the cotyledons, with up to eight pairs or more before alternates (Brendel 1876, Henry 1910; and pers. obs.). Across its range, americana is mostly tetraploid and natural hybrids with other species are unknown; 2n = 56, versus 28 in all other elms of N. America. But Whittemore & Olson (2011) have recently shown that many southeastern plants are diploids, especially from mid-Atlantic states to the Cumberland Plateau. Moreover, there are rare triploids and pentaploids, perhaps resulting from hybridization (Haugen & Bentz 2017; Whittemore & Xia 2020). Although morphological distinction is not clearly apparent, tetraploids may have larger glossier leaves on average, with more abruptly acuminate apices and more asymmetric, relatively broad-shaped bases (A. Whittemore, pers. comm.). Most of the widely distributed cultivars are tetraploid or suspected so (Haugen & Bentz 2017); The disease-resistant "Valley Forge" has leaves that are unusually large and glabrous on upper surfaces, even in young trees.