AMERICAN 
JOURNAL OF BOTANY 
Vol. VIII March, 1921 No. 3 
A STUDY OF RHUS DIVERSILOBA WITH SPECIAL 
REFERENCE TO ITS TOXICITY 
James B. McNair 
(Received for publication September 15, 1920) 
Rhus Toxicodendron (L.), Rhus radicans (L.), and Rhus diversiloba 
T. & G. form a triad of plants equally regarded with aversion. The 
general recognition of their deleterio.us character is evinced in the applica- 
tion of the names poison ivy, poison vine, and poison oak, given to them in 
various parts of the United States. 
Perhaps the earliest mention of these plants in North America is the 
following description by Captain John Smith in 1609: 
The poisonous weed, being in shape but little different from our English yvie; but 
being touched causeth reddness, itchinge, and lastly blysters, the which, howsoever, after a 
while they passe awaye of themselves without further harme; yet because for the time 
they are somewhat painefull, and in aspect dangerous, it hath gotten itselfe an ill name* 
although questionlesse of noe very ill nature. 
Long before the birth of Linnaeus, Cornutus in 1635 described the plant 
as a species of ivy in his work on the plants of Canada {Hedera trifolia 
Canadensis Corn. 96 from Carolina in the British Herbarium). 
About 1736 Linnaeus classified this plant as Toxicodendron triphyllum 
glabrum. At the same time he described and named Rhus radicans. 
In an entry dated October 9, 1748, Peter Kalm gave an extensive and 
interesting description in his travels in North America of the Rhus radicans 
of Linnaeus. Since that time there have been many accounts of these 
plants and of their toxic nature. 
In 1820, Bigelow described Rhus radicans of Linnaeus as having 
Ternate leaves, that grow on long semicylindrical petioles. Leaflets ovate or rhomboidal, 
acute, smooth and shining on both sides, and veins sometimes a little hairy beneath. The 
margin is sometimes entire and sometimes variously toothed and lobed, in the same plant. 
The flowers are small and greenish white. They grow in panicles or compound racemes on 
the sides of the new shoots and are chiefly axillary. The barren [male] flowers have a calyx 
of five erect, acute segments, and a corolla of five oblong recurved petals. Stamens erect 
with oblong anthers. In the center is a rudiment of a style. The fertile [female] flowers 
situated on a different plant, are about half the size of the preceding. The calyx and corolla 
are similar but more erect. They have five small, abortive stamens and a roundish germ 
[ovule] surmounted with a short, erect style ending in three stigmas. The berries are 
roundish and of a pale green color, approaching to white. 
[The Journal for February (8: 59-126) was issued March 19, 1921.] 
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