Ironweeds Not Iron-clad

By Marion Lobstein, Botany Chair, Prince William Wildflower Society and Professor Emeritus, Northern Virginia Community College

Most of approximately 20 species ofVernonia or ironweeds are native to North America out of roughly 500 species worldwide. Referencing theFlora of Virginia, there appears to be significant taxonomic changes to three species: Vernonia noveboracensis (New York ironweed), V. glauca (upland ironweed), and V. gigantea (tall ironweed). Exploration of the taxonomic history of the species and genus reveals a number of earlier taxonomic changes. Linnaeus assigned the genus Serratula noveboracensis to V. noveboracensis, S. glauca to V. glauca, and perhaps S. altissima forV. gigantean in his 1753 Species Plantarum. John Clayton and Johann Gronovius in the 1762 second edition of Flora Virginica used the genus Serratulato designate species of ironweed included in this work.

Andre Michaux is credited with first collecting specimens in the American Colonies, perhaps in the Carolinas, of Vernonia noveboracensis, New York ironweed. Henry Gleason in 1953 used V. harperi for V. noveborencensis but V. harperi is no longer accepted as a synonym for V. noveboracensis. In 1788, Walter used the genus Chrysocoma for V. noveboracensis, proposing C. tomentosa and V. gigantea as C. gigantea. Asa Gray in his1884 work referred to V. glauca as V. noveboracensis var. latifolia, but by 1894 Nathaniel Britton referred to it as V. glauca.

Of the three Virginia species of VernoniaV. gigantea has undergone the most change, having been classified as Chrysocoma gigantea by Thomas Walter in Flora Caroliniana(1788) and as Cacalia gigantea by Otto Kuntze (1891). V. gigantea has primarily gone back and forth from V. altissima by Thomas Nuttall in 1818 and even in more recent floras, such as the Flora of West Virginia (1978); in the 7th   and 8th editions (1908 and 1950 respectively) of Gray’s Manual of Botany; in the Manual of the Flora of the Carolinas (1968); and in popular wildflower books such as Peterson’s and Newcomb’s wildflower guides.

Vernonia glauca

In 1983, however, Britton and Brown listed V. gigantea in the Illustrated Flora of the Northern States and Canada, as did Arthur Cronquist in the 1991 Manual of Vascular Plants of Northeastern United States and Adjacent Canada (2nd ed.).

Chrysocoma as a genus is still in use but for other members of the Asteraceae. Serratula is still used for a quite a few of Old World species of Vernonia. Other groups of composites, such as Cirsium thistles and Centaurea knapweeds, have drifted in and out of the genus Vernonia.

When I started researching for this article, I did not realize how extensive taxonomic changes were involving our three Virginia species of ironweed. It would seem that scientific names are not Iron(weed)-clad, but instead undergo many changes over time.

In a future article, I will explore changes in the genus of Joe-Pye Weeds from Eupatorium(1753) to Eutrochium (1818); back to Eupatorium in most of the later 1800s and 1900s; toEupatoriadelphus (late 1900s); and, now, once again back to Eutrochium.

Nothing is iron-clad in taxonomy!