CATEGORIES

I. Species is generally considered to be the basic unit of taxonomy but there is debate on the definition of species and species concepts vary, depending on the group and investigator.

II. Infraspecific categories are used to describe populations that show some degree of differentiation. That categories that are most often used are subspecies and variety.

III. A genus is a group of species that have more in common with each other than with other species. Generic concepts also vary in different groups.

IV. The family is a grouping of similar genera. This is the highest category in which most are considered to be monophyletic groupings.

V. Order includes one or more related families. It becomes very difficult to insure that a monophyletic group has been circumscribed at this and higher levels.

VI. The Subclass is the category that serves as the backbone of Cronquist's classification. Boundaries become very difficult to draw at this level.

There are other classifications that vary more or less from Cronquist's system. Go to The Flowering Plant Gateway to take a more detailed look at Cronquist's system and compare it with two other systems.

Recently, phylogenetic trees, which can be used to develop classification systems, have been constructed using phenotypic and genotypic characters (especially DNA sequences). We will contrast one of these gene trees with Cronquist's system near the end of the semester.

A Short Synopsis of Cronquist's System

1 Division - Magnoliophyta

2 Classes - Magnoliopsida (Dicots) and Liliopsida (Monodots

Subclasses

Orders

Families - the larger, more common and economically important families will be covered

Dicots - 6 subclasses, 64 orders, 318 families, 170,000 species

Monocots - 5 subclasses, 19 orders, 65 families, 50,000 species