- Flowerless seed plants fall within the gymnosperm plant classification.green plant image by isatori from Fotolia.com
Seed plants fall within two general categories made up of flowering and non-flowering plants. Flowerless seed plants, also known as gymnosperms, appear in tree form as conifers, and in plant form as gnetales and ginkgoes. And while gymnosperms are known for their non-flowering characteristics, some varieties may function as cross-over species from flowerless to flowering plant types. - The word "gymnosperm" comes from the Greek language and translates as "naked seed." According to Fulton-Montgomery Community College, naked seeds are what differentiate flowerless plants from the more evolved flowering varieties known as angiosperms, which carry their seeds inside protective coverings. Conifers appear as tree-plants, some of which include pine, cypress, juniper and spruce trees. Conifers produce seeds in the form of cones that sit on the surface of their leaves. Cones come in both male and female varieties. The actual fertilization process relies mostly on wind currents that blow male pollen particles into female cone structures. Once the fertilized egg develops, it too is blown away to find suitable soil conditions from which a new tree-plant takes root.
- Gnetale flowerless seed plants grow primarily in desert-type and semi-arid, tropical conditions. According to the University of Nevada, Ephedra, Welwitchia and Gnetum are the three categories of gnetales plants in existence today. Of the four gymnosperm categories of plants, gnetales most resemble flowering plants in terms of the water-conducting tissues found in their stems and the flower-like structures they produce. Like the flowering varieties, gnetales also use a double fertilization process that's designed to produce a fertilized egg and a nutrient-rich endosperm covering for the egg. In the case of gnetales, the cells that develop into the endosperm casing never reach maturity, but instead die off.
- The name "Cycad" originates from the Greek word "kykas," meaning "palm,"which is the most distinguishing characteristic in this plant breed. According to the University of Nevada, cycads appear as fern-like plants with leaves made up of palm-like fronds. These plants grow primarily in tropical and sub-tropical climate conditions, though some varieties can grow in desert-like climates as well as along rocky terrains. Cycads grow into male or female plant forms, with the female plants housing the seeds while the male plants house the cones, according to the Palm and Cycad Societies of Florida. The male cones contain the pollen particles used to fertilize the seed structures located on the leaves of the female plant. Wind currents, insects and animals aid in the fertilization process by transporting the pollen particles to the female seed structures.
- The only existing breed of ginkgoes appears as the ginkgo biloba tree made up of fan-shaped leaves and plum-sized seeds. Like cycads, ginkgo tree-plants grow up as either males or females. According to the University of Nevada, male trees house small pollen cones along leaf surfaces, while the females produce seeds that appear at the end of leaf stalks. Fertilization processes are the same as those for cycad plants, though wind serves as the primary mode of transportation for trees because of their height. Gingko seeds provide the material for the gingko biloba herb supplement.
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