Gymnosperms

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 * GYMNOSPERMS

Gymnosperms are a group of vascular plants whose seeds are not enclosed by a ripened ovary, like a fruit. The seeds of many gymnosperms are borne in cones and are not visible. In other words, they are found as cone-bearing plants. They are the most ancient surviving seed plants. The term gymnosperm comes from the Greek word //gumnospermos//, which means "naked seeds." It refers to the unenclosed condition of the seeds, as when they are produced they are found naked on the scales of a cone or similar structure.

Taxonomists now recognise four distinct divisions of extant gymnospermous plants, which include gnetophytes, cycads, ginkgoes, and conifers.

About 70 present-day species of the phylum gnetophyta are known. The reproductive scales of these plants are clustered into cones.
 * GNETOPHYTES**

They are members of the phylum Cycadophyta. They are palmlike plants that reproduce with large cones. Cycads first appeared in the fossil record during the Triassic Period, 225 million years ago. Huge forests thrived when dinosaurs were still alive. Today, there are only nine genera of cycads. They can be found growing naturally in tropical and subtropical places such as Mexico, the West Indies, Florida, and parts of Asia, Africa, and Australia.
 * CYCADS**

Ginkgoes were common during the Dinosaur Era, but today the phylum Ginkgophyta contains only one species, //Ginkgo biloba//. It is considered a living fossil since the living species looks similar to its fossil ancestors. It may even be the oldest seed plant species alive today. Ginkgo trees were cultivated in China, where they were often planted around temples. They are now often planted in urban settings in the United States, where their toughness and resistance to air pollution make them popular shade trees.
 * GINKGOES**

Conifers are the most common gymnosperms, with more than 500 known species. The phylum Coniferophyta includes pines, spruces, firs, cedars, sequoias, redwoods, and yews. Some can live for more than 4000 years (e.g. bristlecone pine tree) Other species can grow up to more than 100 meters in height (e.g. giant redwoods) Today, conifers thrive in a wide variety of habitats (montains, sandy soil, etc.) Conifer leaves have specific adaptations to dry conditions. Scientists hypothesized that more than 250 million years ago, when conifers evolved, climate conditions were dry and cool. In response to these conditions, most conifers developed leaves that are long and thin (needle-like). This shape reduces the surface area from which water can be lost by evaporation. Another water-conserving adaptation is the thick, waxy layer that covers conifer leaves. In addition, the openings of leaes that allow for gas exchange are located in cavities below the surface of the leaves, also reducing water loss.
 * CONIFERS**

Most conifers are "evergreens," where they retain their leaves throughout the year. The needles of most conifer species remain on the plant for 2 to 14 years. The trees never become bare as needles are constantly replaced. However, not all species are evergreen. Larches and bald cypresses lose their needles every fall.