Last week I discussed how the scientific names of plants change because of the law of priority. This time around, I explain how names change due to differences in species concepts, leaving the question of “what is a species” for future posts. For now, all you have to know about this complex topic is that a species is a population of plants that plant taxonomists recognize as being different from other populations. In addition, a useful species concept is one in which the morphological and molecular characters used to circumscribe species are also apparent to non-botanists. For example, non-botanists should be able to identify one species from another based on character differences.
In simplest terms, botanists are classified as those who recognize relatively small differences in plant populations as distinct species (splitters), versus those who consider certain kinds of variation to be normal within a species (lumpers). Many animal species include considerable variation in their circumscription as evidenced by the recognition of humans, dogs, and cats as single species. Generally speaking, zoologists have broader species concepts than botanists with the latter tending to split species more than the former. Botanists with different philosophies about splitting and lumping may cause name changes.
Now in week three, Henry Hurd Rusby‘s Mulford Expedition arrives in Peru after passing through the Panama Canal. Anchoring in Callao, several of the expedition’s number travel on to Lima as guests of the Peruvian leadership. Gathering medicines, touring the capital, and meeting with newspaper representatives are the orders of the day, yet the trials of surviving abroad play out even in the relative safety of urban Peru.
Reboarding the Santa Elisa, the expedition steams southeast to Mollendo where the competitive business of hotel porterage and questionable exchange rates preface the expedition’s journey into higher altitudes. There Rusby’s talents as a botanist are finally put to use identifying cacti, mountain trees, and local vegetables on the road to Arequipa.
One of our easiest to recognize wildflowers is Jack-in-the-pulpit (Arisaema triphyllum). Named for its fancied resemblance to a preacher (“Jack”) in his over-hanging pulpit, the name captures the imagination and makes the plant easy to remember. Like other members of the aroid family (Araceae) the inflorescence is comprised of two parts: a spadix that bears numerous small flowers and a modified leaf called a spathe that surrounds and partially encloses the spadix. In the case of Jack-in-the-pulpit, each plant bears either male or female flowers; the plants are dioecious.
Other aroids can have different arrangements of their flowers; for example the flowers of skunk cabbage (Symplocarpus foetidus) are perfect, meaning that every flower has both male and female parts, while those of the European wildflower known as lords and ladies (Arum maculatum), are arranged with separate male flowers on the upper part of the spadix and female flowers on the lower part.
Week two of Henry Hurd Rusby‘s Mulford Expedition sees the Santa Elisa passing through the Panama Canal (see Week One). At the time of this writing, the Canal has been open for less than seven years, and as we read, construction is ongoing. The Canal’s most profound immediate effect is a quicker and safer journey between the Atlantic and Pacific Oceans. A voyage from New York to San Francisco saves over 7,800 miles and the ship avoids navigating the hazardous Drake Passage and Cape Horn.
Dr. Rusby mentions the ceremony of the Court of Neptune, also known as the Line-crossing Ceremony, whereby a commemoration of a sailor’s first crossing of the equator is performed. This ceremony is also performed for passenger’s entertainment aboard civilian ocean liners such as the Santa Elisa. Few details are given by Dr. Rusby, but the ceremony has its colorful characters, including the King of Neptune and Davy Jones.
Columbine, with its nectar-filled red spurs, blooms just at the time that hummingbirds are returning from their winter sojourns south of the border—or is it the other way around? Do hummingbirds return just when the columbine begins to flower? From either viewpoint, it is clear that these two species have coevolved to synchronize their arrival in spring.
Hummingbirds need a plentiful source of nectar to provide the energy required for their frenetic life style. In return they incidentally transport pollen from one flower to the next ensuring that the columbine will be fertilized and set seed, thus perpetuating the species. Some hummingbirds will become summer residents here, while others will continue their northward migration as far as Canada, following the columbine bloom north.
Memorizing scientific names can be an exasperating experience for nature lovers, especially when learning that those names occasionally change for complicated reasons. Last week I discussed the structure of scientific names based on the Linnaean binomial system. Now, I explain some of the most common ways scientific names change based on the law of priority, a rule stipulating that the first name validly published for a species is the correct name for it. Be aware that this may not be the most beginner-friendly topic, but it is integral to understanding the complex business of botanical nomenclature.
The rules of botanical nomenclatures are formalized in the International Code of Nomenclature (ICN), which is updated every five years at the International Botanical Congresses; the most recent such congress took place in Melbourne, Australia, in 2011. Although the ICN defines the rules for naming plants, it does not provide guidance for determining if a species is distinct from other published species, thus justifying a new name. The taxonomic validity of species is determined by reviewers of scientific papers in which names are either proposed or changed, as well as by the acceptance of the names by the scientific community in their scholarly works such as Floras.
In 1921, when Henry Hurd Rusby was 65 years old, he embarked on his last field trip to South America as the Director of the Mulford Biological Exploration of the Amazon Basin. Professor of Botany and Materia Medica, and Dean of the College of Pharmacy at Columbia University, Rusby had much experience exploring in South America. The goal of the Mulford Biological Expedition was the discovery of plants with possible pharmaceutical properties.
Understanding the botanical naming system can be a difficult task for beginners—classification hierarchy, plant name changes, and name selection all have to be taken into account. But rather than tackle this important botanical puzzle all at once, we instead begin with the most basic piece: species names. The rules discussed here apply not just to the Brazil nut family, but to every plant found in all the world’s habitats, and have much in common with zoological nomenclature.
A species name consists of two parts—Gustavia augusta, for example. The first part of the name is the genus and the second is the species epithet, each of which is either in Latin or Latinized words from other languages, especially Greek. Known as binomial nomenclature, Carl Linnaeus is considered the first to use this system, which he employed in his Species Plantarum—long regarded as the starting point for plant nomenclature. As such, a name used in Species Plantarum has priority over other names published for the same species at a later date.
Gustavia augusta L. was published in a later, 1775 edition of Species Plantarum, but afterward the same species was published as Gustavia antillana Miers in 1874. In this case, Gustavia augusta is considered the correct name, and G. antillana is accepted as a synonym.
In telling the tale of one of the great Amazonian explorers, C.V. von Martius, I wrote that, “… Martius was carrying with him 20,000 botanical specimens which served, and continue to serve, as the basis for countless botanical studies, including Flora Brasiliensis which remains the only published complete Flora of Brazil to this day.” To clarify, I was not suggesting that Flora Brasiliensis contains all Brazilian species, but that it is the only Brazilian Flora that included all documented plant species in Brazil at the time of its writing. In fact, there are at least twice as many species known in Brazil today as there were back then!
The leaves of Virginia bluebell sprout each spring in such deep shades of purple that they are difficult to see against the dark soil. As the leaves mature, the purple coloration is gradually lost until they become a soft green. Flowers, too, undergo a color change, from pink in bud to a lovely shade of blue shortly before the buds open.
The floral color change is not uncommon in members of this family, the Boraginaceae (borage family). Its members include forget-me-not (Myosotis spp.), viper’s bugloss (Echium vulgare), and lungwort (Pulmonaria spp.), all of which have pink buds opening as blue flowers. The color change is due to changes in the pH of the cell sap, and, like some hydrangeas, plants growing in more acidic soils will have flowers of a deeper shade of blue. Members of the borage family also share in common the shape of their inflorescence, referred to as a scorpioid cyme for the way it uncoils like a scorpion’s tail. A true spring ephemeral, the leaves of Virginia bluebells turn yellow soon after the flowers have finished blooming and are gone by late June.