Plants dominate our planet and our lives, thanks largely to their diversity and remarkable adaptations. And now, we will discuss the nature and extent of the diversity of plants, which includes the distinguishing features of each group of organisms.
Bryophytes include mosses, liverworts, and hornworts. Although bryophtes are most noticeable when they grow in dense mats, they can grow just about everywhere —including on bark and exposed rocks, where other plants cannot grow. Bryophytes are especially common in moist areas and lack the specialized vascular tissues that characterize other groups of plants.
Seedless vascular plants, also known as pteridophytes, share features with bryophytes, including the same types of pigments, the basic life cycle, and the storage of starch as their primary food reserve. However, the evolution of vascular tissue enabled vascular plants to invade and dominate the drier habitats on land more effectively than could non-vascular plants. Most species of seedless vascular plants are true ferns, but they also include horsetails, whisk ferns, and club mosses. Most varieties of these plants live in tropical areas.
Gymnosperms are plants whose pollen goes directly to ovules (unfertilized seeds) instead of to a stigma (as in the flowering plants) and whose seeds are naked (i.e., are not enclosed in fruits). Thus, by definition, gymnosperms are all fruitless seed plants. Examples of gymnosperms include maidenhair tree (Ginkgo), cycads, conifers, and members of the Gnetophyta (e.g., Ephedra, Gnetum).
Flowering plants are the most successful of all plant groups in terms of their diversity. The group includes more than 250,000 species and at least 12,000 genera. This group is often referred to as the angiosperms because their seeds are enclosed in a carpel. The carpel is the primary feature that distinguishes angiosperms from gymnosperms. Angiosperms live in almost all terrestrial and aquatic habitants on earth. Except for conifer forests and moss-lichen tundras, angiosperms dominate all of the major terrestrial zones of vegetation.
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