What the heart wants: adaptive significance of cordate leaf morphology in Arnica (Asteraceae)

We studied how the leaf inclination of basal leaves of two species, heartleaf arnica (Arnica cordifolia Hook.) and broadleaf arnica (Arnica latifolia Bong.) varied with canopy cover in the Greater Yellowstone Ecosystem, Wyoming, USA in July and August, 2022. Basal leaves of heartleaf arnica possess cordate leaf bases while those of broadleaf arnica do not, leading to potential biomechanical limitations of the latter to persist in shaded forest understories. Leaf inclination was measured as the angle (degrees) between the petiole and leaf planes of basal leaves for each species; cordateness was measured as the ratio of leaf length on either side of the petiole insertion point in basal leaves of heartleaf arnica. Data collection are complete.