Poison sumac grows as a coarse woody shrub or small tree (fig. 19) and
never in the vinelike form of its poison-ivy relatives. This plant is
known also as swamp sumac, poison elder, poison ash, poison dogwood, and
thunderwood. It does not have variable forms, such as occur in poison-oak
or poison-ivy, and botanists agree to call it _Rhus vernix_. The area in
the Eastern States where it is likely to be found is chiefly eastward
from eastern Minnesota, northeastern Illinois, Indiana, central Kentucky
and Tennessee, and southeastern Texas, as shown on the shaded area of the
map, figure 20. This shrub is usually associated with swamps and bogs,
and the most typical growth occurs along the margin of an area of wet
acid soil.
_Figure 21._--Small branch of poison sumac with six compound leaves.
_Figure 22._--Fruit of poison sumac, one-third natural size. These fruits
somewhat resemble those of poison-ivy. They are always on drooping
slender stems attached at the side of the small branches and are never
terminal as in the species of sumac that are not poisonous.
The plants range in height from 5 or 6 feet to small trees that may
attain a height of 25 feet. The poison sumac shrub shown in figure 19
is growing on the edge of a swamp and is quite typical of the general
appearance of the larger shrubs, which approach a treelike form. As a
rule the shrubs do not have a symmetrical upright treelike appearance.
They are more or less inclined to lean and have branched stems with about
the same diameter from the ground level to the middle height of the shrub.
Occasional isolated plants are found outside of swampy regions.
Apparently these plants are started from seed distributed by birds. The
plants in dry soil usually do not become more than a few feet tall. They
are likely to cause poisoning to unsuspecting individuals, as single
isolated plants are not readily recognized, especially out of their usual
region.
The leaves of the poison sumac are divided into 7 to 13 leaflets,
arranged in pairs with a single leaflet at the end of the midrib (fig.
21).
_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.
The leaflets are an elongated oval shape without teeth or serrations on
the margins. They are 3 to 4 inches long and 1 to 2 inches wide, with a
smooth velvetlike texture and bright orange color when they first appear
in spring. Later they become dark green and glossy on the upper surface
and pale green on the lower and have scarlet midribs. Early in fall they
turn to a brilliant red-orange or russet shade.
The small yellowish-green flowers are borne in clusters in slender stems
arising from the axis of leaves along the smaller branches. The slender
clusters of flowers have much the general appearance of the poison-ivy
flower, but hang in much longer clusters. The flowers mature into
ivory-white or green-colored fruits resembling those of poison-oak or
poison-ivy, except that they are usually less compact and hang in loose
clusters that may be 10 to 12 inches in length (fig. 22).