Distinguishing Impatiens capensis from Impatiens pallida (Balsaminaceae) using leaf traits

<p><i>Impatiens capensis</i> (orange jewelweed) and <i>Impatiens pallida</i> (yellow jewelweed) are annual species with similar phenotypes that grow in similar environments throughout the eastern United States. This makes them extremely difficult to distinguish when (chasmogamous) flowers are absent. We use morphometric analyses to identify leaf characters that distinguish these species. After collecting and scanning 342 leaves from plants of each species growing in co-occurring populations in Madison, WI, we quantified: leaf size, shape (using elliptical Fourier analysis), serratedness, and color. Using leaf size and shape traits, a linear discriminate analysis assigned up to 100% of leaves to the correct species. The uppermost fully expanded leaf yielded the most accurate species assignments based on size and shape traits. This leaf was on average, smaller, less deeply serrated, with a more acute base, apex, and elliptical shape in <i>I. capensis</i> as compared to <i>I. pallida. Impatiens pallida </i>leaves had more color contrast (lighter veins and margins) than <i>I. capensis</i>, which were solid green throughout. Morphometric analysis is a promising technique to identify species-distinguishing characters in the absence of binary traits or molecular genetic analyses. Leaves from across these species' ranges should be analyzed to test the robustness of the species-distinguishing characters we present.</p>