SKALSKY, JEANNIE* and MANOJ MISTRY. Department of Biology, Butler Hall, MS 3258, Texas A&M University, College Station, Texas 77843. - Fractal analysis of leaf edges.
The genus Silphium (Asteraceae) is comprised of roughly 15
species, which are limited to eastern and central United States.
Naturally occurring hybrids have not been documented, though they have
been produced artificially. Two species, S. laciniatum , which
is wide spread, and S.albiflorum , endemic to Texas, were
utilized for this study. S. laciniatum has large leaves, some
over two feet long each, which are very laciniate and lobed.
S.albiflorum , which is theorized to have evolved from S.
laciniatum , is smaller and also has laciniate leaves. The larger
leaves overlap when they are folded to fit inside a plant press so
analysis of entire leaves from typical herbarium specimens is
impossible. This also prevents accurate measurements of leaf area,
etc. and limits the amount of data gathered from an individual plant.
Fractals are traditionally used to analyze geographic structures, such
as coastlines. Defined as irregular fragmented shapes that exhibit
intricate structure at all sizes so that details are reminiscent of
the entire object, fractal measurements utilize different box sizes to
measure a perimeter. A smaller box size provides a larger value for
the perimeter. When fractals were used to measure small portions of
leaves from S. laciniatum , S.albiflorum and putative
hybrid populations, PCA analysis revealed delineation between the two
species with the putative hybrid intermediate.
Key words: Fractal, leaf margin, Silphium (Asteraceae)