Families of Vascular Plants - EEB337H1

What are plant species and sub-specific taxa?


In this course, three taxonomic categories feature prominently: family, genus, and species. Species are particular kinds of plants. For example, we know that there are particular kinds of pines, belonging to the genus Pinus, such as white pine (P. strobus), red pine (P. resinosa), or jack pine (P. banksiana). Note that the species names just given were explained by reference to English common names (white pine, red pine, jack pine) as these were thought to be familiar to most readers of this web page. Also note the way in which the genus "Pinus" was spelled out, and then abbreviated, as "P." Note too the use of italicization for all scientific names at the level of genus and below; these rules are spelled out by a freelance editor in her blog HERE.

It is important to note that all species names are binomials, that is, they actually consist of two names: that of the genus (capitalized) to which the species belongs (e.g. Pinus), and then the epithet (uncapitalized) that denotes which species belonging to this genus is being referred to, white, red, or jack pine in the example above. The idea of naming species with binomials was introduced by the 18th century Swedish botanist Linnaeus (1707-1778) as part of a comprehensive reform of the way in which the natural world is named and classified. Note that binomials had been used earlier by Gaspard Bauhin (1560-1624), but without any formal recommendation to adopt such an approach. Note also that the genus + species binomial corresponds to the noun + adjective format that is encountered in folk taxonomies. It has been suggested that in fact Linnaeus' system for naming plants represents a formalization of pre-existing European folk taxonomies. The noun + adjective format of scientific names should also make it clear why species must always be referred to by their binomial, since the species epithet by itself (e.g. "strobus," "resinosa," or "banksiana") provides no information about its referent, the genus to which the species in question belongs. You can make the same observation about adjectives in general: reference to, say, "the puce," will simply bring the response, "the puce what???"

Species (abbreviated sp.; plural, spp.) in the abstract can be thought of as lineages represented at any given time by populations of interbreeding individuals all of whom share a common ancestor (and so are monophyletic). In practice, however, even though species are considered the fundamental units of evolution it is difficult or impossible to come up with a single basis for deciding what is a species. This is because we cannot know with certainty the genealogical relationships between individuals sampled at different times and places from a population of usually unknown size and distribution. Nevertheless, we can extrapolate from what we know about patterns of morphological, anatomical, and chemical variation, about plant genetics and breeding systems, as well as about plant distributions and plant ecology to arrive at what are in most cases useable, working definitions of species. Inevitably, in almost all of the vascular plants in checklists like Muskoka Flora the species concept employed is basically a morphological one, although in many cases it is bolstered by data from other sources. What this means is that most species will be recognizable from their morphology because they exhibit either several characteristics that are altogether unique, or else unique patterns of covariation between characteristics that individually might show overlapping variation between species.

Judd et al. 2008 (ch. 6) review species concepts currently in use.

Subspecies (ssp.) are commonly used to recognize the existence of regional variants of a species, that is some degree of morphological differentiation (not as great as that between species) accompanies geographic (or ecological, or temporal) separation from other subspecies. Subspecies are employed frequently in the checklist of Ontario vascular plants by Morton and Venn (1990).

Varieties (var.) are often used to recognize the existence of local variants, although the choice between subspecies and varietal status in some groups is sometimes more a matter of personal taste than of adherence to a strict definition. Varieties are frequently employed in the account of the orchids of Ontario by Whiting and Catling (1986).

Forma (f.) is used most often to recognize variants that occur sporadically across the range of a species and that are distinguished by only one or a few features, such as an unusual flower color. Forms are used frequently in Gray's Manual (Fernald 1970). as in the rare, white-flowered Aquilegia canadensis forma albiflora.

Checklists such as the Muskoka Flora from which the text on this page has been adapted are built upon the accumulated experience and knowledge of not only its authors, but also of all the workers over the past three or more centuries who have progressively refined the concepts of the taxa presented here. As the checklist is completed you will be able to see, if you care to, how in some places the authors may have agreed with one taxonomic opinion, and disagreed with others, so that the way in which names are used, or the taxonomic level at which they are used, is not necessarily the same as in other treatments of the same plants. Nevertheless, this checklist remains a valid description of the plants of Muskoka District for the following reasons: (1) it is specimen-based, i.e. all of the taxa listed are documented by herbarium specimens, so that identifications can be checked and the use of names verified; (2) the scientific names used are given in full, with authorities, so that a particular taxon concept can be traced back to the original author responsible for it; and (3) the authors provide a complete bibliography of the taxonomic and floristic references consulted in the course of producing their treatment.

In the academic context of this course it is also worth noting that species concepts are once again the subject of active debate, as systematists must grapple with the need to classify organisms that exhibit contrasting patterns of reproductive behavior, and for which widely varying amounts of information are available.

The complete names of plant taxa include identification of the authority responsible for the name, or for the combination in which it appears. Click here to learn more about authorities. Each name of a species is also associated with a type specimen; consult a textbook on plant taxonomy in order to learn more about the type method as practiced by botanical systematists. The standard form for the names of plant taxa can be accessed on the International Plant Names Index (IPNI) web site.

Click on the FNA logo to access the article by Stebbins (1993) on concepts of species and genera: Flora North America - Introduction.


| What are plant families? | How do we distinguish them? | How and why do we study them? | Selected vascular plant families of Ontario | Reading List | Course outline |

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Please send your comments to tim.dickinson@utoronto.ca; last updated 17-Jan-2014