Figure 23.—A, Smooth sumac and dwarf sumac growing in a mixed stand. These plants are not poisonous. B, Terminal fruiting spike of smooth sumac, about one-seventh natural size. This form of terminal fruiting spike is typical of all the species of sumac that are not poisonous.
CONFUSION OF POISONOUS AND HARMLESS SUMACS
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.
