Family - Anacardiaceae

Stems - Typically vines or shrubs, often with aerial roots, rhizomatous, woody, typically reddish in the herbaceous portions. Young shoots densely pubescent to hirsute, greenish.

Leaves - Alternate, petiolate, trifoliolate. Petioles densely pubescent. Leaflets ovate, coarsely serrate or lobed to entire, acute to acuminate, glabrous to pubescent above and below. Petiolules of lateral leaflets to 5mm long. Terminal leaflet to +13cm long, +8cm broad, on petiolule to 4cm long. All petiolules densely pubescent.

Inflorescence - Axillary paniculate thryse to +10cm long. Axis of thryse densely pubescent. Pedicels to 2mm long, pubescent. Plants dioecious.

Flowers - Petals 5, free, yellowish-green, 1.7mm long, 1.1mm broad, glabrous, oblong, obtuse at apex, spreading to reflexed. Staminate flowers with 5 stamens. Stamens alternating with petals. Filaments whitish to yellowish, glabrous, broader at base than at apex. Anthers orange, 1.2mm long. Pistillate flowers with a globose ovary. Ovary superior, glabrous. Style short, 3-lobed. Pistillate flowers often with staminal vestiges. Stigmas whitish to yellowish. Sepals 5, green with yellow on margins, glabrous, lance-ovate, 1.1mm long, 1mm broad, united at base. Drupes globose, creamy white to tannish, +/-4mm in diameter.

Flowers.

Flowering - May - July.

Habitat - Prairies, woodlands, glades, waste ground, fence rows, bluffs, thickets, roadsides, railroads, nearly everywhere.

Origin - Native to U.S.

Other info. - As you may have guessed by now, this is the classic "Poison Ivy" that most folks are afraid of. I won't go on and on about how allergenic this plant is but I do want to say that most people are not immediately allergic to the plant. The allergy is acquired through contact over a period of time with the volatile oils in the tissues of the species. It took me 30 years to become only mildly allergic to the plant. The only way to know for sure if your allergic is to come into contact with the plant and see what happens.
Toxicodendron means "Poison Tree".
This species is highly variable in leaf shape, leaf pubescence, and growth habit. I won't go into the many varieties here but I will say the plant described above is typical of nearly all of the Missouri material.
An old synonym is Rhus radicans L.

Photographs taken at the Kansas City Zoo, 6-2-00, and in the Ozark Scenic Riverways, Shannon County, MO., 5-18-03.