Because of the same general appearance of several common species of
sumac and the poison sumac, considerable confusion has occurred as to
which one is poisonous. Throughout most of the range where poison sumac
grows, three other species are the only ones that are likely to be
confused. These are the smooth sumac (_Rhus glabra_), staghorn sumac (_R.
typhina_), and dwarf sumac (_R. copallina_). All the nonpoisonous species
have red fruits that together form a distinctive terminal seed head,
as shown in figure 23. These are easily distinguished from the slender
hanging clusters of white fruit of the poison sumac, as shown in figure
22. Sometimes more than one species of the harmless sumac grow together,
as shown in figure 23, _A_.
When seed heads or flower heads occur on the plants it is easy to
distinguish the poisonous from the harmless plants; however, in many
clumps of either kind, flowers or fruit may not develop. Fortunately,
the leaves have some rather distinct characteristics, which can be
easily observed. Figure 24 shows leaves of the three harmless species as
compared with poison sumac.
The leaves of the smooth sumac (fig. 24, _A_) and of the staghorn sumac
(fig. 24, _B_) have many leaflets, which are slender lance-shaped with a
toothed margin. In these species there are usually more than 13 leaflets.
The leaves of the dwarf sumac (fig. 24, _C_) and the poison sumac (fig.
24, _D_) have fewer leaflets, and these are more oval-shaped, with smooth
or even margins.
The dwarf sumac, however, may be readily distinguished from the poisonous
sumac by the winged midrib of the leaf (fig. 24, _E_). There is
considerable variation in the size of the wing margin along the midrib,
which in some cases may be reduced almost to a line between the leaflets.
The winged midrib is more prominent near the terminal leaflet and can
always be detected. The midrib of the poison sumac is never winged. A
little study of the fruit and the leaf characteristics of the poisonous
and harmless species will make it possible to avoid the poisonous one and
utilize the other, which has considerable value as an ornamental plant,
as a source of commercial tannin, and for controlling erosion on waste
hillsides.
_Figure 24._--Leaves of species of sumac that are often confused: _A_,
Smooth sumac; _B_, staghorn sumac; _C_, dwarf sumac; _D_, poison sumac;
_E_, enlarged portion of dwarf sumac leaf from _C_, showing the wing
margin of the midrib. Poison sumac does not have the winged midrib.