In seed plants, each female gametophyte, and the spore that gives rise to it, is hidden within the sporophyte and is entirely dependent on it for nutrition. Male gametophores right are topped with antheridia that produce sperm. Each plant produces either functionally male flowers or functionally female flowers. If separate staminate and carpellate flowers are always found on the same plant, the species is called monoecious. The condition is thought to represent a transition between bisexuality and dioecy.
In the commoner narrow sense of the term, it refers to plants with unisexual flowers which occur on the same individual. Spores may be identical isospores or come in different sizes microspores and megaspores , but strictly speaking, spores and sporophytes are neither male nor female because they do not produce gametes. However, Amborella plants may change their "sex" over time. In the bryophytes liverworts , mosses and hornworts , the sexual gametophyte is the dominant generation. The population produces normally male or female plants with unisexual flowers, but some plants may have bisexual flowers, some both male and female flowers, and others some combination thereof, such as female and bisexual flowers. For example, a sporophyte that produces spores that give rise only to male gametophytes may be described as "male", even though the sporophyte itself is asexual, producing only spores. Structurally, the flowers may be bisexual, consisting of two stamens and an ovary, or may be male staminate , lacking a functional ovary, or female carpellate , lacking functional stamens. This situation is reached in the female flowers of duckweeds Lemna , which comprise a single carpel, and in the male flowers of spurges Euphorbia which comprise a single stamen. In this species, gametes are produced on different plants on umbrella-shaped gametophores with different morphologies. The sepals and petals together form the perianth. Stamens may be called the "male" parts of a flower and collectively form the androecium. The condition is thought to represent a transition between bisexuality and dioecy. This promotes outcrossing by limiting self-pollination. A mature alder tree Alnus species produces long catkins containing only male flowers, each with four stamens and a minute perianth, and separate stalked groups of female flowers, each without a perianth. A "unisexual" flower is one in which either the stamens or the carpels are missing, vestigial or otherwise non-functional. If the carpel contains more than one seed, as in Eranthis hyemalis , it is called a follicle. For example, Arisaema triphyllum Jack-in-the-pulpit expresses sexual differences at different stages of growth: The sporophyte of a flowering plant is often described using sexual terms e. Other terms used for this condition are androgynous, hermaphroditic, monoclinous and synoecious. Similarly, flowers produced by the sporophyte may be described as "unisexual" or "bisexual", meaning that they give rise to either one sex of gametophyte or both sexes of gametophyte. It too is dioecious; at any one time, each plant produces either flowers with functional stamens but no carpels, or flowers with a few non-functional stamens and a number of fully functional carpels. Arisaema triphyllum thus covers a multitude of sexual conditions in its lifetime: Amborella represents the first known group of flowering plants to separate from their common ancestor. A gametophyte can be monoicous bisexual , producing both eggs and sperm or dioicous unisexual , either female producing eggs or male producing sperm. Flowers vary enormously in their construction morphology.
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