Fossil spores show that land plants (embryos) have existed for at least 475 million years. Early land plants reproduced sexually with flagellated, floating spermatids, like the green algae from which they evolved. An adaptation to terrestrialization was the development of upright meosporangia for dispersal by spores to new habitats. This trait is not lacking in the descendants of their closest algal relatives, the Caryophician green algae.
Subsequent terrestrial adaptation was accompanied by the retention of the gametophyte, the delicate, vascular sexual stage, within the tissues of the vascular sporophyte. This resulted in the germination of the spore within the spore rather than releasing the spore, as occurs in non-seeded plants. A current example of how this can happen can be seen in precocious spore germination in Selaginella, spike-moss. The consequence for the ancestors of angiosperms was enclosing them in a case, the seed. The apparently sudden appearance in the fossil record of almost modern flowers and in great diversity posed such a problem to the theory of evolution that Charles Darwin called it an «abominable mystery». However, the fossil record has expanded significantly since Darwin’s time, and the recent discoveries of angiosperm fossils such as Archifractus, as well as further discoveries of fossil gymnosperms, show how angiosperm characteristics were acquired in a series of stages. The service of houston every day flower arrangements and roses in houston is easily available at the houston floral shops.
Several groups of extinct gymnosperms, especially seed ferns, have been proposed as ancestors of flowering plants, but there is no consistent fossil evidence of how flowers evolved, and botanists still consider this a mystery. Some older fossils, such as Upper Triassic Samiguelia levisii, have been suggested. Earlier seed plants, such as ginkgo, and conifers (such as pines and firs), did not produce flowers. The pollen grains (male gametophytes) of ginkgo and cycad produce a pair of flagellated, mobile sperm cells that «swim» up the developing pollen tube to the female and her eggs.
Olin, a secondary metabolite produced by many flowering plants, has been found in Permian deposits of that era, as well as fossils of gigantopterids. Gigantopterids are a group of extinct seed plants that share many morphological traits with flowering plants, although they are not themselves flowering plants.