Figure 18.—Western poison-oak: A, Top of shrub, with leaves and fruit; B, clusters of fruit after leaves have fallen.
Low-growing plants, especially those exposed to full sunlight, are often quite woody and show no tendency for vining. Low-growing plants with woody stems are common in pasture areas or along roadsides. Livestock in grazing do not invade the poison-ivy shrub, and as a rule these plants continue to spread both by root-stock and seed.
Figure 19.—A large poison sumac shrub about 15 feet tall, growing on the edge of a swamp.
Figure 20.—The shaded area shows the region where poison sumac is likely to occur in bogs or swamps, although isolated plants are sometimes found in dry soil.
As in other ivy the leaves consist of three leaflets with much irregularity in the manner of lobing, especially of the two lateral leaflets. The Latin name dirersiloba refers to the irregularity occurring in the shapes of the leaves on different plants and on the same plant or even irregularity in the lobing of leaflets of the same leaf. Sometimes lobes occur on both sides of a leaflet, thus giving it somewhat the semblance of an oak leaf. The middle or terminal leaflet is more likely to be lobed on both sides and resembles an oak leaf more than the other two. A study of the leaves shown in figures [15] and [17] shows the variation in lobing. Some plants may have leaflets with an even margin and no lobing whatsoever, as those in [figure 15, B]. The surface of the leaves is usually glossy and uneven, so that they have a thick leathery appearance.