Several criteria are used to classify plants. Historically, flower morphology has been the primary determinant of classification, but biochemical and genetic data are increasingly important.
The two major plant phyla are the gymnosperms (conifers, cycads, Ginkgo) and angiosperms (flowering plants). The Angiosperms are further divided into two major classes---the Monocotyledonae (monocots) and the Dicotyledonae (dicots).
The division of flowering plants into monocots and dicots was first proposed by John Ray in 1682. In modern taxonomy, the classes Magnoliopsida (dicots) and the Liliopsida (monocots) are often used.
Definition of a Dicot
A dicot is so named, because it produces two special leaves---the cotyledons---upon germination. These embryonic leaves are "seed leaves" that quickly fall off or shrivel up, and they do not look like the later leaves that are typical of the plant.
Dicots generally have a distinct taproot with a few major lateral branches. The roots are seldom fibrous as they are in monocots.
In dicots, the vascular bundles (xylem and phloem) are arranged in a ring close to the outside the stems. In monocot stems, the vascular bundles are arranged more randomly.
Dicot leaf veins form branched networks, often described as net-like. Monocots have veins running parallel to the length of the leaves.
Dicot flower petals are usually found in multiples of four or five. Monocot petals occur in multiples of three and are limited to a maximum of six.
- Vascular Plant Families; James P. Smith; Madd River Press, Eureka, CA; 1977
- Class Magoliopsida (Dicots)
- Photo Credit Photo by Tico Bassie (http://www.flickr.com/photos/tico_bassie/120810354/)
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