Lines, outlines, and landmarks:: morphometric analyses of leaves of Acer rubrum, Acer saccharinum (Aceraceae) and their hybrid

Quantitative comparisons of leaf morphology for evaluating taxonomic relationships may be conducted by traditional morphometries, outline analyses, or geometric morphometries. These approaches were employed for examining relationships among trees of two species of maple, Acer rubrum and A. saccharinum, and their hybrid (A. xfreemanii). Leaf samples from six hybrid trees (three each from two accessions) and 40 trees field identified as either species were pressed and dried. Leaf outline and landmark data were captured for each leaf, and linear and angular measures were derived from the landmark configurations. A vector of character means, a mean leaf outline, and a consensus landmark configuration were generated for each tree. Traditional morphological measurements, a single-parameter outline descriptor, elliptic Fourier coefficients of the outlines, and relative warp scores for the landmarks were used to depict relationships among the 46 OTUs. All three data types reveal similar patterns with respect to the two species, and the hybrids are generally intermediate between the two species. The results provide evidence of genetic segregation in one hybrid accession, that several of the field sampled trees are naturally occurring hybrids, and that relative warps analysis can reveal aspects of shape variation not detected by the other analyses.