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The stigma, together with the style and ovary (typically called the stigma-style-ovary system) comprises the pistil, which is part of the gynoecium or female reproductive organ of a plant. The stigma itself forms the distal portion of the style, or stylodia, and is composed of stigmatic papillae , the cells of which are receptive to pollen.
Flower of Magnolia × wieseneri showing the many pistils making up the gynoecium in the middle of the flower Hippeastrum flowers showing stamens, style and stigma Hippeastrum stigmas and style Moss plants with gynoecia, clusters of archegonia at the apex of each shoot.
Some flowers may self-pollinate, producing seed using pollen from a different flower of the same plant, but others have mechanisms to prevent self-pollination and rely on cross-pollination, when pollen is transferred from the anther of one flower to the stigma of another flower on a different individual of the same species.
Close-up of a Schlumbergera flower, showing part of the gynoecium (specifically the stigma and part of the style) and the stamens that surround it. 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.
The stigma plays a role in guiding the sperm to a receptive ovule, in the case of many ovules. [11] Only compatible pollen grains are allowed to grow as determined by signaling with the stigma. In the pollen grain, the generative cell gives rise to the sperm, whereas the vegetative cells have a tube cell that grows the pollen tube.
Longitudinal section of female flower of a squash showing pistil (=ovary+style+stigma), ovules, and petals. The petals and sepals are above the ovary; such a flower is said to have an inferior ovary, or the flower is said to be epigynous. Cross section of a tulip ovary
The stigma sits at the apex of the column in the front but is pointing downwards after resupination (the rotation by 180 degrees before unfolding of the flower). [citation needed] This stigma has the form of a small bowl, the clinandrium, a viscous surface embedding the (generally) single
The pollen is carried to the pistil of another flower, by wind or animal pollinators, and deposited on the stigma. As the pollen grain germinates, the tube cell produces the pollen tube, which elongates and extends down the long style of the carpel and into the ovary, where its sperm cells are released in the megagametophyte.