Ivy, Hedera helix, is a woody evergreen climber of European woods and walls, clinging by aerial rootlets and staying green through the hardest winter. In the classical world it was the plant of Dionysus, the Greek god of wine and ecstasy (the Roman Bacchus): his followers wore ivy wreaths, his sacred staff, the thyrsus, was wound with ivy and vine, and ivy was thought to temper the heat of wine, so that a wreath of it was worn against drunkenness. An ivy bush hung outside a building marked it as a tavern, the origin of the old saying that good wine needs no bush.
The word ivy also names a modern American institution: the Ivy League, referring to a group of old northeastern universities whose historic buildings were often covered in climbing ivy, was used informally from the 1930s before being formalised as the name of an intercollegiate athletic conference in 1954, a purely secular and modern extension of the plant's old association with venerable age and unbroken continuity. Outside Europe ivy has become an ecological liability rather than a blessing: English ivy, Hedera helix, is classed as an invasive species across much of North America, where its climbing growth smothers native trees and its groundcover shades out understory plants, a modern conservation problem quite apart from its ancient status as the plant of Dionysus.