I am doing some research that involves monitoring ash (Fraxinus spp.) populations in Michigan and Ohio. Green ash (Fraxinus pennsylvanica, also referred to as red ash) and white ash (Fraxinus americana) are difficult to distinguish. We have been using habitat (upland vs. riparian), leaf scars (U-shaped vs. shield-shaped), and bark (depth of furrows) to tell them apart, but we know that none of these characteristics are absolute. It would be nice to have a definite, yet inexpensive, method to check our identifications.
Sylvia May Obenauf Taylor (1972), "ecological and genetic isolation of Fraxinus americana and Fraxinus pennsylvanica", describes a method of distinguishing the two species based on the presence or absence of papillae on the lower leaf surface. "Microscopic examination of lower epidermis of leaflets was made by means of epidermal peels made by spreading Duco Cement (a synthetic adhesive) on the surface of either fresh or dried leaves. When dry, the cement was removed and mounted on glass slides... The papillae are finger-like projections present on the lower epidermal cells of white ash leaves, but never on the leaves of red ash." So my questions to you are: 1. Do you have any experience with epidermal peels? If so, what kind of adhesive do you use? If we press and dry the leaves this summer, will we be able to do the peels and see the papillae this winter? 2. Do you know of any good pictures of papillae of Fraxinus or other species? 3. Is the presence of papillae still accepted as a good way to distinguish these species? Thank you for your help! -Kathleen --------------------------------------------- Kathleen S. Knight Research Ecologist USDA Forest Service Northern Research Station
