Monocots versus Dicots - Monocots and Dicots

Monocots versus Dicots
University of California
Museum of Paleontology

The Two Classes of Flowering Plants

The history behind the classes.
Traditionally, the flowering plants have been divided into two major groups, or classes,: the Dicots (Magnoliopsida) and the Monocots (Liliopsida). Many people take this separation into two classes for granted, because it is "plainly obvious", but botanists have not always recognized these as the two fundamental groups of angiosperms. Although Theophrastus (circa 370 BC) is credited with first recognizing differences between the two groups, classification of plants was based upon overall growth form -- trees, herbs, vines -- until the 1600s.

In 1682, John Ray published his Methodus Plantarum Nova, in which Dicotyledones and Monocotyledones were first given formal taxonomic standing. This system was popularized by the French botanist Antoine Laurent de Jussieu in his Genera Plantarum of 1789, a work which improved upon, and gradually replaced, the system of plant classification devised by Linnaeus.

The fuzzy distinction between the classes.

Even after the general acceptance of Monocots and Dicots as the primary groups of flowering plants, botanists did not always agree upon the placement of families into one or the other class. Even in this century some plants called paleoherbs have left problems for taxonomy of angiosperms. These plants have a mix of characters which do not occur together in most other flowering plants. For instance, the Nymphaeales, or water lilies, have reticulate venation in their leaves, and what may be a single cotyledon in the embryo. It is not clear whether it is a single lobed cotyledon, or two which have been fused. The water lilies also have a vascular arrangement in their stem similar to that of monocots.

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