Plant taxonomy (more recently known as plant systematics) is the branch of botany that deals with the identification, grouping (classification), and naming (nomenclature) of plants.
Depending on the expert consulted, there are thought to be anywhere from 350,000 to 500,000 species (separate kinds) of plants with more being discovered all the time. This overwhelming diversity of plant kinds presents a formidable and ongoing task for the botanical taxonomist.
There are a number of different plant classification systems employed by biologists and botanists with adjustments and refinements constantly being made to those different systems.
Morphology-Based Plant Taxonomy Systems
For over two hundred and seventy years, taxonomists have developed classification systems based on the morphology (physical structure) of living things. In our modern morphological system of plant classification all living things are divided into three domains: the Bacteria—“modern” bacteria that live in ordinary habitats; the Arachae—ancient bacteria that live in extreme habitats, and the Eukarya—organisms whose cells contain a nucleus.
All the true plants lumped together comprise the next smaller level of organization known as a kingdom. The kingdom is composed of divisions; divisions are composed of classes; classes are composed of orders; orders are composed of families; families are composed of genera and genera are composed of species.
Each group (taxon) is progressively smaller and more specific that the one above it. The species level consists of one very exclusive type of plant and one only.
Thus, any plant is classified into a total of 8 groups with each group growing progressively smaller and more specific than the one before it. Each group is then given a Latin name.
Phylogenetic Plant Taxonomy Systems
Within the past two decades another classification scheme known as cladistics or phylogenetics has been gaining favor with taxonomists. Phylogenetics uses certain features of plants known as derived characters and the genome (genetics) of plant species to establish evolutionary relationships between groups in order to construct their family tree.
Shared derived characteristics are strong evidence of common ancestry between organisms that share them. Evidence used to establish evolutionary relationships is in the form of common morphology between groups as well as molecular and DNA tests comparisons.
It should be noted that there is not total agreement among botanical taxonomists on exactly how plants should be classified. Despite the importance of taxonomy to biologists, the only taxon (group) that has a clearly definable identity is the species. The taxa above the level of species, however, are more difficult to define and do not have a clear biological identity.
A Traditional Plant Classification System
- Domain Eukarya
- Kingdom Plantae
- Phylum (Division) Bryophyta (Mosses)
- Phylum (Division) Hepatophyta (Liverworts)
- Phylum (Division) Anthocerophyta (Hornworts)
- Phylum (Division) Psilotophyta (Whisk ferns)
- Phylum (Division) Lycophyta (Club Mosses)
- Phylum (Division) Sphenophyta (Horsetails)
- Phylum (Division) Pterophyta (True ferns)
- Phylum (Division) Cycadophyta (Cycads)
- Phylum (Division) Ginkgophyta (Ginkgo)
- Phylum (Division) Gnetophyta (Gnetales)
- Phylum (Division) Coniferophyta (gymnosperms or conifers)
- Phylum (Division) Anthophyta (angiosperms or flowers)
Class Monocotyledonae (Monocots)
- Embryo with a single cotyledon; leaves predominantly parallel veination; flower parts in multiples of three; vascular bundles scattered throughout stem. About 65,000 species. Examples: lily, corn, grasses, iris, palm, tulip, orchid.
Class Dicotyledonae (Dicots)
- Embryo with two cotyledons; leaves with veination in netlike patterns; flower parts in multiples of fours or fives; vascular bundles arranged in rings within stem. About 250,000 species. Examples: rose, sunflower, maple, oak, daisy, apple.
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