What Is the Function of the Anther on a Flower?

The anthers develop and distribute pollen.
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The ​anther​ of a flower is a structure in the ​stamen​, the male part of a flower. Not all flowers have stamens. The anther of a flower is vital for plants that reproduce sexually through the process of pollination.

Stamen Function

The stamen is made up of the filament and anther. The function of the ​filament​ is to keep the anther connected to the flower and make it accessible to pollination vectors. Pollen is produced and then released through the anther to pollination vectors like the wind or animals.

The vector then transfers the pollen onto the ​pistil​, the female part of a flower, where pollination begins. ​Perfect flowers​ are those that have both male and female parts (both a stamen and a pistil), and ​imperfect flowers​ are those that have either male or female parts (a stamen or a pistil, but not both).

Identifying the Anther

The anther is a bulbous structure covered in yellow pollen when looking at a flower in full bloom. Stamen and anther size will vary from flower to flower, depending on the pollination vector it has evolved alongside. For example, lilies (​Lilium​ spp.) have relatively long filaments and prominent anthers where the pollen easily rubs off, making it easy to deliver it to their insect pollinators.

In perfect flowers, typically, the central structure is one or a cluster of pistils with the stamens surrounding the pistil. In imperfect flowers, the male flowers, like kiwifruit (​Actinidia deliciosa​), have only stamens and no pistils. Female kiwifruit flowers are an exception because they have both pistils and stamens, but the anthers don't produce functioning pollen.

Anther Morphology

Anthers are made up of two structures called ​thecae​. The thecae (singular: theca) are attached to the filament through a tissue called the ​connective​. Each theca contains two ​microsporangia​ (singular: microsporangium), which typically fuse into one chamber called a ​locule​. Pollen grains are produced inside the microsporangia.

The majority of flowers are ​dithecal​, meaning their anthers have two thecae and four microsporangia. Few plants, mainly those in the canna-lily (Cannaceae) and mallow (Malvaceae) families, are ​monothecal,​ meaning their anthers only have one theca and two microsporangia.

Orchids (Orchidaceae) are unusual in their anther development. Orchid anthers are called ​pollinium,​ which means all the pollen grains of their thecae are joined together, forming a singular mass.

Anther Attachment

Anthers are attached to filaments in different ways. Most anthers are connected at their base to the apex of the filament; this is called ​basifixed​. When the filament is attached to the back of the anther near the base, this is called ​subbasifixed​. ​Dorsified​ attachment is where the filament is connected to the center back of the anther.

All three types of anther attachment can be either versatile or fixed. ​Versatile attachments​ mean that the anther can freely pivot around the point of connection. When touched by a pollinator, freely moving anthers may facilitate the transfer of pollen to a pollination vector more efficiently.

Anther and Pollen Development

The microsporangia contain a column of cells called ​microspore mother cells​. These cells are surrounded by a tissue called the ​tapetum​. While the anther develops, the microspore mother cells go through a process called ​meiosis​, which splits the mother cell into four haploid microspores. The haploid microspores undergo ​mitotic division​ to form a mature pollen grain.

Multiple layers surround each pollen grain. The outermost layer, called the ​exine,​ is thought to be formed from the tapetum. The exine contains numerous macromolecules - one of these is sporopollenin, a highly durable structure unlike anything else that protects the pollen grain. The innermost layer is called the ​intine​ and is produced by the pollen grain itself.

Mature Pollen Grains and Pollination

Pollen grains contain a ​generative cell​ and a ​vegetative cell​. The generative cell produces the sperm cells. After the pollen grain leaves the anther and reaches the stigma of a female flower, pistil pollination is triggered. During pollination, the vegetative cell forms the pollen tube, which the sperm cells use to travel down the style to the flower's ovaries, where it combines with the ovules, completing the pollination process.

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