7.10: Seed Plants
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What does "gymnasium" mean?
Today a gymnasium means a place for playing indoor sports. In ancient Greece, sports were done in the nude, so the word "gymnasium" is based on the Greek word for naked (gymnos). The root word is the same for "gymnosperm," which means "naked seed." Gymnosperms are those plants that do not have a fruit encasing the seed.
Gymnosperms have seeds, but they do not produce fruit. Instead, the seeds of gymnosperms are usually found in cones.
There are four phyla of gymnosperms:
Conifers, members of the phylum Coniferophyta, are probably the gymnosperms that are most familiar to you. Conifers include trees such as pines, firs, spruces, cedars, and the coastal redwood trees in California, which are the tallest living vascular plants.
Conifers have their reproductive structures in cones, but they are not the only plants to have that trait (Figure below). Conifer pollen cones are usually very small, while the seed cones are larger. Pollen contains gametophytes that produce the male gamete of seed plants. The pollen, which is a powder-like substance, is carried by the wind to fertilize the seed cones that contain the female gamete (Figure below).
Conifers have many uses. They are important sources of lumber and are also used to make paper. Resins, the sticky substance you might see oozing out of a wound on a pine tree, are collected from conifers to make a variety of products, such as the solvent turpentine and the rosin used by musicians and baseball players. The sticky rosin improves the pitcher’s hold on the ball or increases the friction between the bow and the strings to help create music from a violin or other stringed instrument.
Cycads, in the phylum Cycadophyta, are also gymnosperms. They have large, finely-divided leaves and grow as short shrubs and trees in tropical regions. Like conifers, they produce cones, but the seed cones and pollen cones are always on separate plants (Figure below). One type of cycad, the Sago Palm, is a popular landscape plant. During the Age of the Dinosaurs (about 65 to 200 million years ago), cycads were the dominant plants. So you can imagine dinosaurs grazing on cycad seeds and roaming through cycad forests.
Ginkgoes, in the phylum Ginkgophyta, are unique because they are the only species left in the phylum. Many other species in the fossil record have gone extinct (Figure below). The ginkgo tree is sometimes called a "living fossil" because it is the last species from its phylum.
One reason the ginkgo tree may have survived is because it was often grown around Buddhist temples, especially in China. The ginkgo tree is also a popular landscape tree today in American cities because it can live in polluted areas better than most plants.
Ginkgoes, like cycads, has separate female and male plants. The male trees are usually preferred for landscaping because the seeds produced by the female plants smell terrible when they ripen.
Gnetophytes, in the phylum Gnetophyta, are a very small and unusual group of plants. Ephedra is an important member of this group, since this desert shrub produces the ephedrine used to treat asthma and other conditions. Welwitschia produces extremely long leaves and is found in the deserts of southwestern Africa (Figure below). Overall, there are about 70 different species in this diverse phylum.
- Gymnosperms have seeds, but they do not produce fruit; the seeds of gymnosperms are usually found in cones.
- There are four phyla of gymnosperms: conifers, cycads, ginkgoes, and gnetophytes.
Use the resource below to answer the questions that follow.
- Gymnosperms at http://www.youtube.com/watch?v=zKnrlUI85ys (4:31)
- Which division of gymnosperm has the most living species? How many species are in this division?
- Where are cycads most abundant?
- Where are conifers most abundant?
- What are the characteristics of conifers?
- What climate change led to conifers becoming more abundant than ferns? When did this occur?
- What features define the gymnosperms?
- What are two examples of conifers?
- Where are the reproductive structures of conifers located?
- What was the dominant plant during the Age of Dinosaurs?
- What gymnosperm is known as a living fossil? Explain your answer.