Classification Hierarchy
Kingdom Plantae
Subkingdom Tracheophyta
Superdivision Spermatophyta
Division Magnoliophyta
Class Magnoliopsida
Subclass Rosidae
Order Sapindales
Class Anacardiaceae
Genus Toxicodendron
Species Toxicodendron radicans
Poison Ivy

Date: May 6, 2008. Location: Kent Park(map)


Scientific Name: Toxicodendron radicans ([L] toxicodendron = poison tree; radicans = root - a reference to the aerial roots on the vining stems) Synonyms: Rhus radicans, Rhus toxicodendron .

Common Name: Poison Ivy

Origin: Native (L48)

Notes: Poison Ivy—in shrub or vine form— is common in disturbed places, roadsides, and wooded areas—some authors treat the shrubs as one species [ T. rydbergii ] and the vining plants as a separate species [T. radicans]. It's best known structure are the "leaflets three" which in spring and autumn display a reddish tint. During the summer growing season they are green. This species is sometimes confused this Virginia creeper (Parthenocissus quinquefolia) which has a similar vining growth habit. See Comparison.

Additional references: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18.

Field Marks for Identification:

Flowers: May, inflorescence is a panicle of yellow to whitish-green five petaled flowers. Fruit: at maturity, a buff colored, subglobose, drupe with an outer brittle epicarp (exocarp), a tough mesocarp, and a thick inner endocarp.

Stems: woody and persistant; vining stems with aerial roots.

Leaves: alternate with petioles 2 to 10 cm long, with 3 leaflets; the terminal leaflet longer stalked than the two laterals.

Glossaries of botanical terms: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

Poison Ivy-1 Poison Ivy-2 Poison Ivy-3 Poison Ivy-4 Poison Ivy-1 Poison Ivy-2 Poison Ivy-3 Poison Ivy-4 Poison Ivy-1 Poison Ivy-2 Poison Ivy-3 Poison Ivy-4 Poison Ivy-3 Poison Ivy-4 Poison Ivy-4 Poison Ivy-3 Poison Ivy-4 Poison Ivy-3 Poison Ivy-4 Poison Ivy-4

Comments: Poison Ivy (and several other members of the family Anacardiaceae) produce Urushiol (pronounced oo-RU-shÄ“-ol) which is a collection of several similar molecules. It is produced by specialized cells in the phloem and found in the waxy cuticle of leaves and in the sap transported through the phloem tissues—particularly in resin ducts located in the phloem. The resin ducts can be seen in this stem section (scroll down to page 11) of a related plant T. vernicifluum (Japanese lacquer tree). The sap is under positive pressure and when any part of the plant is damaged the sap exudes from the wound. When the yellowish sap is exposed to air it turns black as the urushiol becomes oxidized. It is in the oxidized state that urushiol becomes an active irritant to human skin.

Understanding how urushinol causes an allergic response in the skin might benefit from a review of the relevant chemistry, skin histology, and immuno chemistry. Recall that benzene is a six carbon ring, phenol is a benzene ring substituted with a hydroxyl group (-OH), a catechol is phenol substituted with another hydroxyl group in the ortho position, urushiol is a substituted catechol with a string of molecules attached to the benzene ring at the carbon adjacent to the second hydroxyl group. The carbon string is designated with the letter R.