A. triphyllum variants in the woods and elsewhere

[Dot Plyler, Chadds Ford PA,zone 6, N+DV]

Have seen A. stewardsonii on sandy stream banks and wood edges in Bedford
County. This one has a different structure--the ridges are quite obvious.
Didn't notice color differences. The atlas, of course, shows plants in many
parts of PA, but not in the southeast.  How does one determine whether color
differences are due to genetics, light or other environmental influences?