Gynoecium (; ; : gynoecia) is most commonly used as a collective term for the parts of a flower that produce and ultimately develop into the fruit and . The gynoecium is the innermost whorl of a flower; it consists of (one or more) pistils and is typically surrounded by the pollen-producing reproductive organs, the , collectively called the androecium. The gynoecium is often referred to as the "female" portion of the flower, although rather than directly producing female (i.e. ), the gynoecium produces , each of which develops into a female gametophyte which then produces egg cells.
The term gynoecium is also used by botanists to refer to a cluster of archegonia and any associated modified leaves or stems present on a gametophyte shoot in , Marchantiophyta, and . The corresponding terms for the male parts of those plants are clusters of antheridium within the androecium. Flowers that bear a gynoecium but no stamens are called pistillate or carpellate. Flowers lacking a gynoecium are called staminate.
The gynoecium is often referred to as female because it gives rise to female (egg-producing) gametophytes; however, strictly speaking do not have a sex, only gametophytes do. Gynoecium development and arrangement is important in systematic research and identification of , but can be the most challenging of the floral parts to interpret.
The word "pistil" comes from Latin pistillum meaning pestle. A sterile pistil in a male flower is referred to as a pistillode.
Carpels are thought to be phylogenetically derived from ovule-bearing leaves or leaf homologues (), which evolved to form a closed structure containing the ovules. This structure is typically rolled and fused along the margin.
Although many flowers satisfy the above definition of a carpel, there are also flowers that do not have carpels because in these flowers the ovule(s), although enclosed, are borne directly on the floral apex. Therefore, the carpel has been redefined as an appendage that encloses ovule(s) and may or may not bear them.Greyson, R. I. 1994. The Development of Flowers. New York/Oxford: Oxford University Press.Leins, P. and Erbar, C. 2010. Flower and Fruit. Stuttgart: Schweizerbart Science Publishers However, the most unobjectionable definition of the carpel is simply that of an appendage that encloses an ovule or ovules.
The degree of connation ("fusion") in a syncarpous gynoecium can vary. The carpels may be "fused" only at their bases, but retain separate styles and stigmas. The carpels may be "fused" entirely, except for retaining separate stigmas. Sometimes (e.g., Apocynaceae) carpels are fused by their styles or stigmas but possess distinct ovaries. In a syncarpous gynoecium, the "fused" ovaries of the constituent carpels may be referred to collectively as a single compound ovary. It can be a challenge to determine how many carpels fused to form a syncarpous gynoecium. If the styles and stigmas are distinct, they can usually be counted to determine the number of carpels. Within the compound ovary, the carpels may have distinct locules divided by walls called septa. If a syncarpous gynoecium has a single style and stigma and a single locule in the ovary, it may be necessary to examine how the ovules are attached. Each carpel will usually have a distinct line of placentation where the ovules are attached.
A carpel has a similar function to a megasporophyll, but typically includes a stigma, and is fused, with ovules enclosed in the enlarged lower portion, the ovary.
In some basal angiosperm lineages, Degeneriaceae and Winteraceae, a carpel begins as a shallow cup where the ovules develop with laminar placentation, on the upper surface of the carpel. The carpel eventually forms a folded, leaf-like structure, not fully sealed at its margins. No style exists, but a broad stigmatic crest along the margin allows pollen tubes access along the surface and between hairs at the margins.
Two kinds of fusion have been distinguished: postgenital fusion that can be observed during the development of flowers, and congenital fusion that cannot be observed i.e., fusions that occurred during phylogeny. But it is very difficult to distinguish fusion and non-fusion processes in the evolution of flowering plants. Some processes that have been considered congenital (phylogenetic) fusions appear to be non-fusion processes such as, for example, the de novo formation of intercalary growth in a ring zone at or below the base of primordia. Therefore, "it is now increasingly acknowledged that the term 'fusion,' as applied to phylogeny (as in 'congenital fusion') is ill-advised."
The relationship of the other flower parts to the gynoecium can be an important systematic and taxonomic character. In some flowers, the stamens, petals, and sepals are often said to be "fused" into a "floral tube" or hypanthium. However, as Leins & Erbar (2010) pointed out, "the classical view that the wall of the inferior ovary results from the "congenital" fusion of dorsal carpel flanks and the floral axis does not correspond to the ontogenetic processes that can actually be observed. All that can be seen is an intercalary growth in a broad circular zone that changes the shape of the floral axis (receptacle)." And what happened during evolution is not a phylogenetic fusion but the formation of a unitary intercalary meristem. Evolutionary developmental biology investigates such developmental processes that arise or change during evolution.
If the hypanthium is absent, the flower is hypogynous, and the stamens, petals, and sepals are all attached to the receptacle below the gynoecium. Hypogynous flowers are often referred to as having a superior ovary. This is the typical arrangement in most flowers.
If the hypanthium is present up to the base of the style(s), the flower is epigynous. In an epigynous flower, the stamens, petals, and sepals are attached to the hypanthium at the top of the ovary or, occasionally, the hypanthium may extend beyond the top of the ovary. Epigynous flowers are often referred to as having an inferior ovary. Plant families with epigynous flowers include Orchidaceae, Asteraceae, and Onagraceae.
Between these two extremes are perigynous flowers, in which a hypanthium is present, but is either free from the gynoecium (in which case it may appear to be a cup or tube surrounding the gynoecium) or connected partly to the gynoecium (with the stamens, petals, and sepals attached to the hypanthium part of the way up the ovary). Perigynous flowers are often referred to as having a half-inferior ovary (or, sometimes, partially inferior or half-superior). This arrangement is particularly frequent in the Rosaceae and Saxifragaceae.
Occasionally, the gynoecium is born on a stalk, called the gynophore, as in Isomeris arborea.
The style and stigma of the flower are involved in most types of self incompatibility reactions. Self-incompatibility, if present, prevents fertilisation by pollen from the same plant or from genetically similar plants, and ensures outcrossing.
The primitive development of carpels, as seen in such groups of plants as Tasmannia and Degeneria, lack styles and the stigmatic surface is produced along the carpels margins.Armen Takhtajan. Flowering Plants . Springer Science & Business Media; 6 July 2009. . p. 22–.
Introduction
Pistil
Carpels
Types
+ Comparison of gynoecium terminology using carpel and pistil
! Gynoecium composition
! Carpel
terminology
! Pistil terminology
! ExamplesSingle carpel Monocarpous (unicarpellate) gynoecium A pistil (simple) Avocado ( Persea sp.), most legumes (Fabaceae) Multiple distinct ("unfused") carpels Apocarpous (choricarpous) gynoecium Pistils (simple) Strawberry ( Fragaria sp.), Buttercup ( Ranunculus sp.) Multiple connate ("fused") carpels Syncarpous gynoecium A pistil (compound) Tulip ( Tulipa sp.), most flowers
Pistil
Gynoecium position
Placentation
The ovule
Role of the stigma and style
See also
Notes
Bibliography
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