Its more westerly native range and apparent xeromorphic foliar traits have led to speculation that black maple (Acer nigrum Michx.f.) is more drought resistant than sugar maple (Acer saccharum Marsh.). We examined differences in morphology and anatomy of leaves of trees of these species indigenous near the 43°N latitude in the midwestern and eastern United States. Leaves were collected during July, Aug., and Sept. 1995, from 10 trees in each of 24 sites at longitudes of 71°W in Maine to 94°W in Iowa. Density of trichomes on abaxial surfaces and lamina surface area showed quadratic relationships with longitude and were greatest for leaves from westerly sites in Iowa. The percentage of total lamina surface area partitioned in the two most basipetal lobes increased linearly with longitude. Abaxial surfaces had 6 to 960 trichomes/cm2, lamina surface area was 28 to 176 cm2, and surface area partitioned in basipetal lobes was 5% to 9%. A quadratic regression function related increases in trichome density to decreasing mean annual rainfall at collection sites. Specific leaf mass ranged from 3.5 to 7.6 mg·cm–2 and did not relate to longitude. Scanning electron microscopy showed leaves throughout the range had similar trichome morphology, and light microscopy is being used to examine variation in leaf anatomy and stomatal traits.
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