Foliar traits of sugar maples and black maples near 43 degrees N latitude in the eastern and central United States

Selection of sugar maples (Acer saccharum Marsh.) and black maples (Acer saccharum Marsh. ssp. nigrum Desm. or Acer nigrum Michx. f.) that will be more resilient than existing cultivars in managed landscapes could be facilitated by defining relationships between geographic origin and foliar traits critical to leaf function. We examined variation in leaf morphology and anatomy of both taxa, known collectively as hard maples, near 43 degrees N latitude and tested for relationships between foliar traits and the longitude of origin from 70 degrees to 94 degrees W longitude. Leaves exposed to direct solar radiation were sampled from up to 20 trees indigenous at each of 42 sites during 1995 and 1996. All leaves from east of 75.84 degrees W and from 92.73 degrees W and further west expressed morphological characters associated with sugar maple and black maple, respectively; leaves with intermediate traits were found between these two longitudes. Leaves from 90 degrees to 94 degrees W had the highest surface area due to increases in the areas of middle and proximal portions of laminae. Up to 1162 trichomes/cm(2) were present on the abaxial surface of laminae from west of 85 degrees W, while laminae from further east were glabrous or had < or = 300 trichomes/cm(2). Laminae from western habitats also had relatively high stomatal frequency, and stomatal apertures of laminae west of 91 degrees W were particularly narrow. Longitude did not affect specific weight and thickness of laminae, which averaged 5.5 mg(.)cm(-2) and 90 micrometers, respectively. Principal component analysis of laminar traits showed existence of two clusters. A large group dominated by data from trees in New England also contained data from trees as far west as approximately equal to 93 degrees W longitude; data for trees further west were clustered separately. Although phenotypic continua were defined, laminae west of 93 degrees W were distinct, which suggests trees selected there may function differently in managed landscapes than trees selected from native populations further east.