by Bob Harms ()

Ash / Fraxinus

F. albicans

The valley of upper Deadman's Creek in N. Hays County has both green ash/red ash (Fraxinus pensylvanica) and Texas (white) ash (F. albicans), and it would seem that hybridization has occurred. They grow along the creek or in bottomland areas that have strong seasonal moisture. 30 years ago the overgrazed land had three very large trees (trunks c. 2' in diameter) and a few saplings. One collapsed some 15 years ago, one large F. albicans (male [staminate]) is still present, and one, F. pensylvanica, has been reduced to a low trunk with a few smaller branches. But the saplings have become trees of moderate size (c. 25-30'), and many new saplings have appeared along the creek.

Determining the species of individual trees has been very challenging. Ash trees are unisexual (dioecious), so the use of samara form is available only for mature female (pistillate) trees. Key leaflet features (as in Shinners & Mahler's Illustrated Flora of North Central Texas) and underleaf coloration do not seem to provide clearcut distinctions for this populations.


"Blades of leaflets lighter green below but not noticeably pale" [p. 848]
— thus F. pensylvanica?

Only recently I discovered a key that employs leaf scars to distinguish the green ash (F. pensylvanica) from the white ash (F. americana). Numerous web sites illustrate this difference. (Google: "leaf scar" "green ash" "white ash".) Since Texas ash is commonly considered to be a variety of F. americana (i.e., F. americana var. texensis), leaf scars provide one possible test to distinguish the two species. With F. albicans the top of the leaf scar is more strongly notched, with a lateral bud in the notch. With F. pensylvanica the top is relatively flat or only slightly notched, with a lateral bud above the scar. This often demands the inspection of several recent leaf scars to make a determination – to locate tokens of an unambiguos scar. Older leaf scars are commonly misleading, as the growing bud has expanded into the top of the scar.

F. albicans F. pensylvanica

The only remaining diagnostic requires a samara (winged fruit) [p. 848]:

F. albicans
Wing of fruit not decurrent on fruit body (wing ± ending where body of fruit begins
F. pensylvanica
Wing of fruit decurrent over half way on fruit body (wind extending along body of fruit)

F. albicans F. pensylvanica
F. albicans F. albicans on left; F. pensylvanica on right Clearly F. pensylvanica

Male, staminate, plants are best identified using leaf scars. The staminate flowers below appear to be on F. albicans, but I am unable to make a safe determination on the basis of this image:

Female, pistillate, flowers do seem to have distinctive calyces, but our sample may be too small to determine this.

F. albicans F. pensylvanica

Fall leaf color may or not reveal the species difference. Numerous trees took on a maroon color. The F. albicans photo at the top of the page was taken the same day as the following, which had never produced samaras, but recent inspection of leaf scars show to be F. pensylvanica.


F. pensylvanica


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