Flowering plants (angiosperms) have ovules and seeds completely enclosed in carpels. The term angiosperms is derived from two Greek words angeion, meaning “vessel,” and sperma, meaning “seed.” The vessel is made up of carpels which become ovaries which become fruits. There is a phylum of flowering plants (Magnoliophyta) and it is divided into two classes which are dicots (Magnoliopsida) and monocots (Liliopsida). Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay Flowering plants are thought to have evolved from a now-extinct ancestor of gymnosperms. Most contemporary botanists of pteridosperms and early flowers had many separate, flattened parts arranged spirally on an elongated receptacle. Flowering plants produce two types of heterosporous spores. Its gametophytes develop in distinct structures. The female gametophyte (megagametophyte) develops within the ovule. Integuments, which later become an integument, surround the megagametophyte. Pollen grains developed in the anthers become male gametophytes. Pollination is the transfer of pollen grains from an anther to the stigma; it is caused by insects, wind and other agents. After pollination, a pollen tube can develop from a pollen grain to the female gametophyte; the nucleus of the tube remains at its end and the generative cell divides, producing two sperm nuclei. After the contents of the pollen tube are discharged into the female gametophyte, a sperm unites with the egg cell to form a zygote; the other sperm unites simultaneously with the two central cell nuclei, forming 3x endosperm. The nutrient tissue of the endosperm may be part of the seed or absorbed by the seed embryo. Due to variations in how a female gametophyte develops, some flowering plants produce 5x, 9x, or 15x endosperm tissue. Some artificial groupings of flowers intended to aid identification do not reflect natural relationships. Sources of evidence used to attempt to naturally group plants include fossils, which suggest that flowering plants first appeared around 160 million years ago. Early flowering plants had simple leaves and numerous spirally arranged flower parts that were not fused to each other; they had both stamens and pistils and were radially symmetrical (regular). Specializations include a decrease in the number of parts, fusion of parts, appearance of compound pistils composed of several individual carpels, inferior ovaries, bilateral symmetry (irregular flowers), and unisexual flowers. Monoecious species have male and female flowers on the same plants. ; dioecious species have male and female flowers on separate plants. Bee-pollinated flowers are delicately sweet and fragrant and tend to be blue or yellow in color. Flowers pollinated by beetles tend to have stronger odors and are usually white or dull in color. Some flowers pollinated by flies give off foul odors. Flowers pollinated by butterflies tend to be white or yellow. Bird-pollinated flowers are usually bright red or yellow and contain lots of nectar but little scent. Most orchids produce pollen grains in pollinia that adhere or attach to parts of visiting insects. The flowers of some.