Ginkgoopsida

Ginkgoales Temporal range: 270–0 Ma PreЄ Є O S D C P T J K Pg N Permian–recent
Jurassic Ginkgo leaves
Scientific classification
Kingdom:	Plantae
Division:	Ginkgophyta
Class:	Ginkgoopsida
Order:	Ginkgoales
Families
Ginkgoaceae †Karkeniaceae †Umaltolepidiaceae †Yimaiaceae †Schmeissneriaceae Incertae sedis †Sphenobaiera

Ginkgoales or Ginkgophyte is a seed plant order containing only one extant species: Ginkgo biloba, the ginkgo tree. It is monotypic, (the only taxon) within the class Ginkgoopsida, which itself is monotypic within the division Ginkgophyta. The order includes five families, of which only Ginkgoaceae remains extant.

The first Ginkgo leaves were found during the Triassic period, but there were many species of Ginkgo during the Jurassic and Cretaceous periods as well. These periods, known collectively as the Mesozoic era, were when diversity and distribution for all plants were at their highest, including in Ginkophytes. It was in the early Cenozoic period that Ginkgophytes nearly became extinct, specifically during the early Cretaceous and Tertiary periods. The only remaining Ginkgophyte was Ginkgo adiantoidses – a polymorphic species. The Chinese were the ones to save Ginkgo, as they grew them in their temple gardens. This is why modern Ginkgo trees are native to China.

Ginkgo trees produce ovulate, pollen-bearing structures. These structures are dioecious, in that male and female structures come from different Ginkgo plants. The pollen organs are very similar to angiospermous catkins. They come from the axils of the bud scales, and the leaves from the Ginkgo tree spur shoots. Pollen is contained in sacs of two to four at the tips of sporophylls on the strobiloid. Ovules of Ginkgo trees come from stalks from leaf axils on the short shoots, each containing two ovules. The ovule is fertilized by the flagellated male gametes, which can move about freely. This fertilization process begins on the tree itself in the spring. The swollen fruit-like ovules, about 2–3 cm in diameter, fall from the tree in the fall, and fertilization continues into the winter/spring.  This fruit contains a single large seed, similar to that of a cycad.

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Wikipedia