Ginkgo biloba, better known simply as ginkgo trees, are the single remaining species of the Ginkgo family of plants. Ginkgophyta and Cycadophyta were dominant plant families from the early Jurassic era to the Pliocene. These gymnosperms were eventually edged out by angiosperms. The life cycle of ginkgo trees is unique, with elements not found in other species.
Ginkgo Biloba
Ginkgo biloba trees are the single remaining species of a plant category that once dominated the earth, in combination with the cycads and ferns. A varied and vigorous family predating the modern flowering plants that now dominate the plant kingdom, the ginkgo displays a number of attributes similar to modern flowering plants, while remaining clearly a gymnosperm (producing a naked seed) rather than an angiosperm (producing fruit). Believed extinct, samples of Ginkgo biloba were found in 1691 in Japan. The tree had been preserved in Chinese Buddhist monastery gardens and from there had passed into cultivation in Japan.
Biologically Unique
The Ginkgo biloba is a unique plant. Not only the sole remaining example of a once varied family of plants, it is also distinct in a number of ways with attributes that, on the one hand, connect it with more primitive ferns and mosses and, on the other hand, share common traits with modern flowering and fruiting plants. Often classified with pines, this gymnosperm is actually quite distinctly different. Ginkgoes have deciduous leaves that turn color and fall with the change of seasons. They produce naked seeds as is common to all gymnosperms, but their naked seeds in many ways mimic the fruiting bodies of angiosperms. Their pollen produces free swimming sperm in much the manner of ferns and mosses, but the female ovules that receive the pollen provide a contained and secure liquid environment for the sperm so that the reproductive process is in large part safe from the environmental risks ferns and mosses face.
Male Trees
The process of reproduction in a Ginkgo biloba plant begins with the production of male and female reproductive organs. Ginkgoes exist as male and female trees, each producing only the organ appropriate to their sex. Male trees produce "catkins," dangling pendant-shaped, pollen producing organs that look rather like tiny green feather boas. These organs produce a four celled pollen which is blown free on the wind until it encounters a female ovule (female sex organ).
Female Tree
The female tree produces an ovule--a seed coat containing four seed cells and a small reservoir of liquid at the open tip. Pollen enters the tip of the ovule and implants in the seed coat, producing an open stem that releases the free swimming sperm which proceed to fertilize the cells of the ovule.
Fertilized Ovule
In fruit bearing trees, the fruit is formed by thickening ovary wall that contains the seeds. Seeds never leave the protection of the ovary wall until the fruit decays or is consumed. In gymnosperms the seed is naked--there is no containing ovary wall. The seed coat is open to the world. In spite of this, the Ginkgo biloba forms what, to most people, appears to be a "fruit." The vital difference is that where a true fruit is formed by the thickening of the ovary wall, the gingko fruit is actually created by the seed coat itself thickening and becoming dense with sugars to feed the future embryonic plants. The ovule is dropped to the ground late in the season, where it decays. Ginkgo fruit is known for the unpleasant smell it creates as it goes bad.
Reproduction
The false fruit of the Ginkgo biloba is intended to be eaten by scavenging animals. The scarified seed is then spread through feces, with the nut shell weakened and ready to be cracked open by the emerging seedling or seedlings, depending on how many cells of the ovule have been fertilized. Reproductive success appears to be best after the nut shell has been scarred and the seed exposed to a period of cold before sprouting is initiated.
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