Color of Pubescence on Bud Scales Conflicts with Keys for Identifying Species of Dirca (Thymelaeaceae)

Abstract

<p>The genus <em>Dirca</em> (Thymelaeaceae) comprises three North American species of deciduous understory shrubs. <em>Dirca palustris</em> (eastern leatherwood) occurs in patchy populations in eastern North America. <a>Nevling (1962)</a> reported that <em>D. palustris</em> ranges from New Brunswick west to Minnesota and Oklahoma, and south to Florida. Guided by herbarium records, we recently confirmed the existence of a large population of <em>D. palustris</em> in northern North Dakota, and the persistence of the species in Nova Scotia, as reported by <a>Gray (1873)</a> and more recently by <a>Soper and Heimburger (1994)</a>. Throughout its broad range, <em>D. palustris</em> generally occurs infrequently but can be locally abundant (<a>Nevling 1962</a>). It is found in populations of variable densities from few to hundreds of individuals per hectare in rich mesic forests (<a>Schulz et al. 2004</a>), and the species often is associated with north- or east-facing stream banks and slopes (<a>Kurz 1997</a>; <a>Nevling 1962</a>). The two other species in the genus are <em>D. occidentalis</em>, endemic near the San Francisco Bay, and <em>D. mexicana</em>, narrowly endemic to the Sierra Madre Oriental in Tamaulipas, Mexico.</p>