Most of the vines or shrubs of poison-ivy produce some flowers that are always in clusters arising on the side of the stem immediately above a leaf. The flowers are rather inconspicuous among the leaves, as may be noted in [figure 7], but they are in quite distinct clusters, as shown in [figure 8, A]. Frequently the flowers do not develop or are abortive and no fruit is produced. When fruits do develop they serve as a positive way of identifying the plant. The berries are not easily confused with the fruits of other plants. They are white and waxy in appearance and have rather distinct lines marking the outer surface, as the segments appear in a peeled orange. These lines may be noted in [figure 8, B], which shows dense clusters of mature fruit about natural size. Some forms of the poison-ivy have the fruit covered with fine hair, giving it a kind of downy appearance; however, in the more common form the fruits are entirely smooth. The fruit is especially helpful in identifying plants late in fall, in winter, and early in spring, when the leaves are not present.
Figure 9.—The shaded area is the region where the eastern oakleaf form of poison-ivy is likely to occur. Other forms also may be in the same region.
Figure 10.—Eastern oakleaf poison-ivy shrub. The upright growth as a low shrub is common. The three parts of each leaf somewhat resembles an oak leaf. The gall formations that cause wartlike protuberances are common on all species.
OAKLEAF POISON-IVY
Of the several kinds of poison-ivy, the oakleaf form occurring in the Eastern and Southern States is more distinctive than some other types. Some people know it as oakleaf ivy while others call it poison-oak, a name more commonly used for the western species discussed later. Botanists have not always agreed upon the scientific name to be applied to this form; however, they now use the name Rhus toxicodendron. Some botanists have used the Latin names R. quercifolia, while others used the name Toxicodendron quercifolium, both of which are more descriptive of the oakleaf form, as the generic name of the oak is Quercus. The area where the oakleaf form may occur, from New Jersey to Texas, is outlined in the map shown in [figure 9]. The common poison-ivy also occurs in some form throughout many parts of this same area.