Plants may be informally grouped into three categories based on structure and mode of reproduction: nonvascular spore plants which are simple in structure (no vascular system) and reproduce by spores, vascular spore plants which are advanced in structure (possess a vascular system) but reproduce by spores, and vascular seed plants which are advanced in structure and reproduce by seeds.
Fossils indicate that nonvascular spore plants and vascular spore plants were the dominant plant types during the age of dinosaurs. However, as the climate underwent a series of upheavals, new group of plants emerged to fill the void; plants that reproduced not by fragile spores but by hardy seeds. The age of seed plants had begun and it has continued unabated to present times.
The vascular seed plants consist of five taxonomic divisions: Cycadophyta, Ginkgophyta, Pinophyta, Gnetophyta, and Magnoliophyta. The first four of these divisions are often grouped into an informal nontaxonomic group known as the gymnosperms (meaning “naked seed”). Their name reflects the fact that their seeds, after maturation, are exposed to the environment (hence, “naked” seed). The Magnoliophyta, or angiosperms as they are informally known, are the flowering plants.
The Types of Gymnosperms
Cycadophyta (Cycads) is a small group of 11 genera and 140 living species; the cycads range in size from short shrubs to moderate-sized long-lived trees and are native to tropical and subtropical regions. Zamia pumila, found in the sandy woods of Florida, is the only cycad native to the United States. Zamia has a stem that is most or entirely underground.
Ginkgophyta (Ginkgo) – Ginkgo biloba (or the maidenhair tree ) is the only living species of this entire division. It is a moderate-sized tree with unique fan-shaped leaves. There are no known wild ginkgo trees and as a species it was thought extinct by Western botanists until it came to light that the plant was considered sacred and had been cultivated for centuries in Chinese temple gardens. The name Ginkgo is Chinese and means “silver apricot.”
Coniferophyta (Conifers) are the most numerous and widespread of the gymnosperms divisions living today with 50 genera and around 550 species.
The basic body plan of nearly all conifer species in North America is that of an evergreen tree. Evergreen in the fact that most of these trees do not drop all their leaves (or in this case, needles) at once in the fall and grow them all back at once in the spring as do deciduous trees.
Examples of conifers include the various types of pines, junipers, spruce, cedar, fir, hemlock, sequoia, and the aforementioned larch and bald cypress. The conifers are the dominant trees in the northernmost forests of the world and on high mountain peaks.
Gnetophyta (Gnetophytes) consists of only three living genera with about 70 species; this small, assorted group contains what are certainly the most unusual of the gymnosperms. They range in body form from shrubs to trees to climbing vines with large leathery leaves.
The desert shrub, Ephedra, is the only economically important member of the gnetales. It produces the alkaloid ephedrine, which is useful in the treatment of bronchial asthma, sinusitis, hay fever, and the common cold.
Conifers Hold Amazing Records
Although the conifers no longer dominate the landscape with their numbers, they still dominate when it comes to size and longevity.
Tallest Living Thing. The coast redwoods (Sequoia sempervirens) or giant redwoods can reach heights over 110 meters (360 feet), the height of a 30-story building.
Most Massive Living Thing. Again, a tip of the hat to the coast redwoods. Not only do they grow tall, they also grow wide having trunk diameters in excess of 11 meters (36 feet). That is wide enough to allow two-lane roads to be tunneled through the trunks of these trees.
When total volume is considered, there is enough wood in one of these trees to build hundreds of homes. Really big ones are calculated to weigh over a thousand tons!
Oldest Living Thing. 10,000 feet up in the White Mountains of eastern California where a few scraggly trees give way to bare, snow-covered rock, resides the twisted and alien-looking bristlecone pine (Pinus longaeva). These nearly-bare trees, gnarled by howling winds, hardly look alive yet amazingly, the oldest has been dated at over 4,900 years.
Imagine counting the rings inward and finding the ring laid down when the Declaration of Independence was signed. Then comes the ring that marks the journey of Columbus to the New World. The tree would have been in its prime during the building of the pyramids and when the ring that marks the year of the birth of Christ, you wouldn’t even be half way through!
The gymnosperms of today are but the scattered remains of an ancient group that once dominated the planet with their size and numbers.
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