But what does it mean when the name of a thing we all thought we knew, like P. bipinnatifidum, suddenly changes?

Sometimes, a name change is inconsequential: A rose is still a rose. In the case of this feathery Philodendron, however, something important has changed: the depth of knowledge about the plant. Philodendron bipinnatifidum Schott ex Endl. was given its name early in the 19th century by the Austrian botanist Heinrich Wilhelm Schott and was validated by his friend and contemporary Stephan Ladislaus Endlicher in 1837. (The last part of the full scientific name honors them.) At the time, botanists had to rely exclusively on morphology, the study of organisms’ forms, when populating the nebulous category of its genus. Yet genus is a frustratingly shaky rung on the taxonomic ladder, not so sharply defined as species (which poses its own challenges), but still less broad than family.

Although biologists sometimes disagree about how to define species or whether a uniform definition applies across all organisms, species exist in nature as populations of real organisms. A genus, like other higher-order taxa, needs to be inferred from the available evidence and is therefore a bit more abstract, vulnerable to incomplete information and subjective judgments.

Today, however, molecular biology is helping to put definitions of genera (the plural of genus) on more solid ground. Digital technologies are also beginning to make it easier to reliably identify and classify rare specimens in remote areas. The recent reassignment of P. bipinnatifidum to a new genus offers a useful glimpse of forces that have been quietly transforming taxonomy and systematics.

The word genus, meaning “kind” or “stock,” goes back to at least 16th-century Latin. The Swiss botanist Gaspard Bauhin was one of the first on record to use the term. In his text from 1620, Pinax theatri botanici (The Illustrated Exposition of Plants), in which Bauhin defined thousands of plant species, he explicitly distinguished between genera and species. It wasn’t until nearly a century later, however, that genus was defined scientifically for plants by the French botanist Joseph Pitton de Tournefort. In his 1694 book Eléments de botanique, ou Méthode pour reconnaître les Plantes, he grouped nearly 7,000 plant species into about 700 genera. Although Tournefort’s definition, based on the morphology of flowers and fruit, was subsequently found to be superficial, the book was popular and botanists continued to use the names Tournefort defined.

Carl Linnaeus, often hailed as the father of modern taxonomy, popularized the word genus further, midway through the 1700s. Linnaeus kept many of Bauhin’s original names when developing his own taxonomic system, and some of them are still in use even today. (Bauhin is fittingly memorialized with his namesake Bauhinia, a genus of flowering trees within the bean family, Fabaceae.)

But much has changed since the days of the original naturalists. The rising importance of the theory of evolution to biology altered the purpose of taxonomy. Taxonomy began simply as a way of naming and cataloging organisms by form, often in keeping with philosophies about a “great chain of being,” a divine hierarchy that held all life. Today’s biologists, however, want systematics and taxonomies to reflect what is understood about evolutionary history, or phylogeny, and the relatedness of different groups.