The Problems with Pilea glauca and Pilea glaucophylla

A small, trailing, groundcovering plant known as Pilea glauca is readily available on the internet. See, for example, the online store of Josh's Frogs or Pernell Gerver's online store. Other web sites list the plant as Pilea glaucophylla. The plant is both common enough and popular enough to have two common names: silver sprinkles and gray artillery plant.

There is, however, one big problem with the name, Pilea glauca. It has never been published. Although the name is in use by the gardening public, the name does not appear in any database of botanical names, including The International Plant Names Index or Tropicos. It is an example of what is known in botany as a nomen nudum, which literally translated means a naked name. In standard botanical practice, each name is tied to a type, that is, an herbarium specimen on which the name is based and each name must be legitimately published if the name is to be considered valid. However, Pilea glauca is floating around the internet completely naked, bereft of the "clothing" provided by a type specimen and legitimate publication.

The name Pilea glaucophylla has neither problem. It was legitimately published in 1936 by E.P. Killip in a publication titled Contributions to the United States National Herbarium and there is a type specimen collected by É.F. André in Colombia and deposited in the herbarium of the Smithsonian's National Museum of Natural History. Unfortunately, there's one small problem: we can search for it at the Smithsonian's NMNH herbarium website and we can see for ourselves that Pilea glaucophylla is a completely different plant than the one circulating on the internet by the name of Pilea glaucophylla.

So, what is the name of this mystery plant? I know that it is definitely not Pilea glauca since that is a nomen nudum that has never been published. And I know that it is not Pilea glaucophylla since that name refers to a completely different plant with erect stems and differently shaped leaves that are about 3-inches (7.6 centimeters) long or longer. I thought that I would never learn its name; however, thanks to the original version of this blog post and the power of the Internet, I heard from David Scherberich of the Jardin Botanique de la Ville de Lyon in France, who informed me that he knows the plant as Pilea libanensis of Cuba. Neither David nor I have confirmed that it is indeed that species by examining vouchered herbarium specimens but a preliminary search on the Internet confirms that Pilea libanensis is very likely the name of our little, silvery, carpeting Pilea.

It is easy to understand how this example of folk taxonomy came about. Pilea libanensis has silvery-green or silvery-bluish leaves that resemble in color the glaucous foliage of some landscape shrubs and trees, especially that of certain conifers. Therefore, at least until now, no one questioned the validity of either Pilea glauca, which means "glaucous Pilea," or Pilea glaucophylla, which means "glaucous-leaved Pilea," because both names aptly fitted the plant. But these incorrect names should not be used and, for now, I am referring to it as Pilea libanensis.

Note: This post was modified from its original version, published on 22 June 2013, by including information in a personal communication by email from David Scherberich dated 12 August 2013.

Image and text © 2013 Rufino Osorio