Living Things

BIOLOGICAL DIVERSITY: SEED PLANTS

Gymnosperms are Seed Plants

Gymnosperms have seeds but not fruits or flowers. Gymnos means naked, sperm means seed: thus the term gymnosperm = naked seeds. Gymnosperms developed during the Paleozoic Era and became the dominant seed plant group during the early Mesozoic Era, as shown in Figure 1. The ancestors of gymnosperms were some now-extinct type of heterosporous fern or related group. There are 700 living species of gymnosperms placed into four divisions: conifers (such as pines and spruce), cycads (such as the sago palm, Cycas revoluta), ginkgos (the maidenhair tree, Ginkgo biloba), and gnetophytes (such as Mormon tea, Ephedra).

BIOLOGICAL DIVERSITY: NONVASCULAR PLANTS AND NONSEED VASCULAR PLANTS

BIOLOGICAL DIVERSITY: NONVASCULAR PLANTS AND NONSEED VASCULAR PLANTS

The plant kingdom contains multicellular phototrophs that usually live on land. The earliest plant fossils are from terrestrial deposits, although some plants have since returned to the water. All plant cells have a cell wall containing the carbohydrate cellulose, and often have plastids in their cytoplasm. The plant life cycle has an alternation between haploid (gametophyte) and diploid (sporophyte) generations. There are more than 300,000 living species of plants known, as well as an extensive fossil record.