Eupatorium semiserratum, commonly called Smallflower thoroughwort, is a herbaceous perennial plant in Asteraceae

Asteraceae

The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...

 native to the Southeastern states of the United States from Florida to South Carolina east to Missouri. The stems grow from 40 to over 100 cm tall and are produced from short rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s. The inflorescence

Inflorescence

An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...

s are composed of a large number of white flowers with disc florets and no ray florets. This species is similar to Eupatorium linearifolium

Eupatorium linearifolium

Eupatorium linearifolium is a fall-blooming herbaceous plant native to North America. Like other members of the genus Eupatorium it has inflorescences containing a large number of white flowers with disc florets and no ray florets....

but has smaller heads of flowers and stems which branch near the tips rather than near the base. The plants previously known as Eupatorium glaucescens or Eupatorium cuneifolium are now classified as E. semiserratum or E. linearifolium.

Another related species is Eupatorium lancifolium

Eupatorium lancifolium

Eupatorium lancifolium commonly called Lanceleaf thoroughwort is a herbaceous perennial plant in Asteraceae native from Alabama, Arkansas, Louisiana and Texas....

, which is found in Alabama, Arkansa, Louisiana, and Texas, and which has sometimes been classified as part of E. semiserratum.