Overview of Plant Categories
This section will give you a brief overview of the different kinds of plants. Subsequent sections will describe some of these kinds of plants in more detail.
All of the different kinds of plants that exist on Earth may be sorted into one of four different categories. These categories are Nonvascular Plants, Seedless Vascular Plants, Gymnosperms, and Angiosperms. These categories are not taxonomic names within the Kingdom Plantae that are simply useful groups to help organize the Kingdom. The taxonomic category for large groups within the Kingdom Plantae is the "division." A division in the plant kingdom is analogous to a phylum in the animal kingdom.
Nonvascular Plants
As their name suggests, the Nonvascular Plants lack vascular tissue. Moss is an example of a nonvascular plant. Vascular tissue in plants is involved with transporting water and nutrients as well as providing physical support for plants. Nonvascular plants are not very large (less than a few centimeters) since they lack the vascular tissue that provides physical support. The nonvascular plants have flagellated sperm that are similar to some of the primitive unicellular algae. Because the sperm are flagellated, water is required for the nonvascular plants to reproduce sexually. The nonvascular plants do produce spores during their lifecycle. Spores are an important advantage to terrestrial life.
Figure 2. This image from Muir Woods near San Francisco shows mosses (bright green nonvascular plants covering the tree trunk on the right), ferns on the forest floor (light green seedless vascular plants), and redwood trees (gymnosperms).
Seedless Vascular Plants
The Seedless Vascular Plants lack seeds but contain vascular tissue. Because they do contain vascular tissue, they can grow to be much larger than nonvascular plants. Like the nonvascular plants, the seedless vascular plants have flagellated sperm and require water so the sperm can swim to the egg.
The taxonomy of the Seedless Vascular Plants is under question. At one time plant taxonomists considered four divisions of Seedless Vascular Plants. The Pterophyta contains the ferns which are familiar potted plants and members of forest floors. The Lycopodophyta contains the club mosses such as "running cedar" or "ground pine." The Psilotophyta contain whisk ferns and the Equisitophyta contain horsetails. Recent evidence suggests these may all be too closely related and that they should be grouped into one division.
Gymnosperms
The Gymnosperms are plants that produce "naked seeds." In other words, their seed is not enclosed in a fruit. Seeds are a very important adaptation for life on land. Gymnosperms contain vascular tissue and can grow to great heights. Water is not needed for their sexual reproduction because they use pollination strategies for the sperm to reach the egg. Pollen is the gametophyte generation. Familiar gymnosperms include pine trees whose seeds are found in pine cones.
There are four divisions of Gymnosperms. The Coniferophyta includes the pine trees. The Ginkophyta includes the Ginko tree. The Cycadophyta includes plants called "cycads." The Gnetophyta is a small division whose members are not familiar to most people. We will not consider the Gnetophyta.
Angiosperms
The Angiosperms are the flowering plants whose seeds are enclosed in a fruit. This is the dominant group of plants on Earth today. They contain vascular tissue and may grow to great heights. Water is not needed for their sexual reproduction because they use pollination strategies. Some plants have and animals have coevolved resulting in some very interesting pollination strategies. The Division Anthophyta is the only division in the group. There are two classes within this division:
- Monocotyledoneae (monocots)
- Dicotyledoneae (dicots).
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