Northern Ontario Plant Database
Why do scientific names change?
Sometimes, without realizing the duplication, botanists in different parts of the world create different names to describe the same species. For example, the name Eriocaulon septangulare (sevenangle pipewort), described in 1937 by Withering, appears in many North American field guides, however, the same plant had previously been described by the English botanist, Druce, in 1909 as Eriocaulon aquaticum.
To deal with situations like this, a set of rules was developed to regulate the naming of species. In botany, these rules are called The International Code of Botanical Nomenclature (ICBN). When dealing with names by different authors that describe the same species, the ICBN dictates that the earliest validly published name is the correct name. This is called the rule of priority and it is one of the main reasons why scientific names sometimes change. The rejected name is considered to be a synonym of the currently accepted name. In our example, the name Eriocaulon aquaticum (1909), although not as well known in North America, has priority over Eriocaulon septangulare (1937). Thus, the accepted name is Eriocaulon aquaticum (Hill) Druce, and Eriocaulon septangulare With. is now considered to be a synonym of Eriocaulon aquaticum.
New research techniques help to clarify relationships
Scientific names may also change when botanical studies show, for example, that a particular species or group of species actually belongs in a different genus, or because a variable species or genus would be better treated as two separate taxa. In the past, these decisions were based primarily on a study of the morphological traits (physical appearance) of the taxa. Since different botanists might interpret the importance of various morphological features differently, there could be several different views proposed by two or more botanists on how the taxa should be treated. Fortunately, with the molecular techniques now available to most researchers, it is possible to show genetic relationships between taxa. Since these techniques have only become popular in the last 15 to 20 years, a lot of work is being done currently to determine the true relationships between organisms at all levels, from Domain to Species level. This recent research has prompted a number of taxonomic changes, which are accompanied by changes in names. A recently published revision of the genus Arabis (Al-Shehbaz 2003), is an excellent example of how molecular research, combined with morphological and cytological studies, have clarified relationships within the Brassicaceae (Mustard Family). The genus Arabis, a large variable taxon with about 80 North American species, has been treated variously by Rollins (1941, 1983, 1993), Löve & Löve (1976), and Mulligan (1996). Al-Shehbaz's research showed that the genus Arabis, in the broad sense (s. lat.), is a polyphyletic group composed of 4 separate lineages. This means that the species traditionally placed in Arabis had actually arisen from 4 unrelated ancestors. Once the molecular relationships were understood, observed morphological differences (in this case, leaf hairs, fruit and leaf shape) and chromosome numbers could be used with confidence to differentiate between genera. So, these North American taxa have now been reassigned to the genera Arabidopsis, Boechera, Pennellia, and Turritis, with just 10 species left in the genus Arabis, in the strict sense (s. str.). For northern Ontario, this means the following changes should be noted: Arabis lyrata (lyreleaf rockcress) is now Arabidopsis lyrata; Arabis glabra (tower mustard) is now Turritis glabra; Arabis canadensis (sicklepod), Arabis divaricarpa (spreadingpod rockcress), Arabis holboelii (Holbøll's rockcress), and Arabis drummondii (Drummond's rockcress) are now, respectively, Boechera canadensis, Boechera divaricarpa, Boechera holboelii, and Boechera stricta; while only Arabis alpina (alpine rockcress), Arabis arenicola (arctic rockcress), and Arabis hirsuta (hairy rockcress) remain unchanged. You can see from the synonyms listed under each of these species that there has been a tremendous amount of confusion about the genera to which these taxa actually belong. Since not all genera or families have been as thoroughly studied yet as Arabis, name changes will most certainly occur for a long while. But as further research clarifies more relationships, we can be certain that the future will bring more stability to the nomenclature.