Unisexual

The male part (androecium) or the female part (gynoecium) of the flower, but not both, can be present in the same flowers. Both the male and female portions of the flower are present in the same flower. They are of two types: monoecious or dioecious flowers. They are also called androgynous flowers. Cross and self-pollination occur in monoecious flowers (those with both male and female parts on the same flower), whereas cross-pollination occurs in dioecious flowers. Cross and self-pollination occur in androgynous flowers (those with both male and female parts on the same flower).

Due to the absence of either male or female parts, they are called the incomplete flower.

They have both male and female parts on the same flower, they are called the complete flower. Example: Papaya, watermelon, corn, etc.

Plant reproductive morphology

Plant reproductive morphology is the study of the physical form and structure (the morphology) of those parts of plants directly or indirectly concerned with sexual reproduction.

Close-up of a flower of Schlumbergera (Christmas or Holiday Cactus), showing part of the gynoecium (the stigma and part of the style are visible) and the stamens that surround it

Among all living organisms, flowers, which are the reproductive structures of angiosperms, are the most varied physically and show a correspondingly great diversity in methods of reproduction. Plants that are not flowering (green algae, mosses, liverworts, hornworts, ferns and gymnosperms such as conifers) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how the sperm from one plant fertilizes the ovum of another, depends on the reproductive morphology and is the single most important determinant of the genetic structure of nonclonal plant populations. Christian Konrad Sprengel (1793) studied the reproduction of flowering plants and for the first time, it was understood that the pollination process involved both biotic and abiotic interactions. Charles Darwin’s theories of natural selection utilized this work to build his theory of evolution, which includes an analysis of the coevolution of flowers and their insect pollinators.

The sporophyte of a flowering plant is often described using sexual terms (e.g. “female” or “male”) based on the sexuality of the gametophyte it gives rise to. 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. 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 the gametophyte.

Flower of Ranunculus glaberrimus

The flower is the characteristic structure concerned with sexual reproduction in flowering plants (angiosperms). Flowers vary enormously in their construction (morphology). A “complete” flower, like that of Ranunculus glaberrimus shown in the figure, has a calyx of outer sepals and a corolla of inner petals. The sepals and petals together form the perianth. Next inwards there are numerous stamens, which produce pollen grains, each containing a microscopic male gametophyte. Stamens may be called the “male” parts of a flower and collectively form the androecium. Finally, in the middle, there are carpels, which at maturity contain one or more ovules, and within each ovule is a tiny female gametophyte. Carpels may be called the “female” parts of a flower and collectively form the gynoecium.

Each carpel in the Ranunculus species is an achene that produces one ovule, which when fertilized becomes a seed. If the carpel contains more than one seed, as in Eranthis hyemalis, it is called a follicle. Two or more carpels may be fused to varying degrees and the entire structure, including the fused styles and stigmas may be called a pistil. The lower part of the pistil, where the ovules are produced, is called the ovary. It may be divided into chambers (locules) corresponding to the separate carpels. 

Most hollies (members of the genus Ilex) are dioecious. Each plant produces either functionally male flowers or functionally female flowers. In Ilex aquifolium (see the illustration), the common European holly, both kinds of flower have four sepals and four white petals; male flowers have four stamens, female flowers usually have four non-functional reduced stamens and a four-celled ovary. Since only female plants can set fruit and produce berries, this has consequences for gardeners. Amborella represents the first known group of flowering plants to separate from their common ancestor. 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 several fully functional carpels. However, Amborella plants may change their “sex” over time. In one study, five cuttings from a male plant produced only male flowers when they first flowered, but at their second flowering three switched to producing female flowers

Conclusion

unisexual flower A flower that possesses either stamens or carpels but not both. A plant may be unisexual (dioecious), possessing only male flowers or female flowers; or it may be monoecious with male and female reproductive organs borne in the same flower or different unisexual flowers but on the same plant.