Plants are upright or sometimes ascending, growing to 1.5 metres (4.9 ft) tall, producing single or multi-stemmed clumps in mid to late summer and fall.

[5] At the end of the upper branches, flat-topped panicles or compound corymbs of white flower heads appear, measuring 5–15 centimetres (2–6 in) across.

[7][8] A. altissima is native to the central and eastern United States, from Texas in the west to Maine in the east and north, and Florida in the south.

[14] During the early 19th century, when large numbers of European Americans from the East, who were unfamiliar with snakeroot, began settling in the plant's habitat of the Midwest and Upper South, many thousands were killed by milk sickness.

[15] It was some decades before European Americans traced the cause to snakeroot, although today Dr. Anna Pierce Hobbs Bixby is credited with identifying the plant in the 1830s.

Signs of poisoning in these animals include depression and lethargy, placement of hind feet close together (horses, goats, cattle) or held far apart (sheep), nasal discharge, excessive salivation, arched body posture, and rapid or difficult breathing.

Ageratina is derived from Greek meaning 'un-aging', in reference to the flowers keeping their color for a long time.