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.
The oakleaf poison-ivy usually does not climb as a vine, but occurs as
a low-growing shrub. Stems are usually upright in their general growth
habit, as they appear in figure 10. The shrubs usually have rather
slender branches, often covered with a fine pubescence that gives the
plant a kind of downy appearance. The leaflets occur in threes, as in
other ivy, but are lobed, somewhat on the general plan of the leaves of
some kinds of oak. The middle leaflet usually is lobed somewhat alike
on both margins and very much resembles a small oak leaf, while the two
lateral leaflets are often irregularly lobed. The leaves shown in figure
11 are a common form. The lighter color on the under side of one of the
leaves (fig. 11, _A_) is due to the pubescence, or fine hairs, on the
surface. The range in size of leaves varies considerably, even on the
same plant; the leaf shown in figure 11, _B_, however, is about natural
size.
The fruit of oakleaf poison-ivy has the same general appearance as the
fruit of common poison-ivy shown in figure 8, although the individual
fruits and stems are often pubescent, while most of the other forms have
a waxy, smooth, cream-colored fruit.
_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.
_Figure 11._--Eastern oakleaf poison-ivy: _A_, Leaves, showing upper deep
green surface and lower lighter colored surface. _B_, Single leaf, about
natural size. The terminal leaflet more nearly resembles an oak leaf than
the two lateral leaflets.