Stigma (botany)

The stigma (plural: stigmas or stigmata[1]) is the receptive tip of a carpel, or of several fused carpels, in the gynoecium of a flower.

Stigma PSFen
Diagram of stigma

Description

2013-05-10 17-37-15-tulipe-44f
Stigma of a Tulipa species, with pollen
Closeup of Stamen and stigma of Lilium 'Stargazer' (the 'Stargazer lily')
Closeup of stigma surrounded by stamen of White Lilium 'Stargazer' (the 'Stargazer lily')

The stigma, together with the style and ovary comprises the pistil, which in turn is part of the gynoecium or female reproductive organ of a plant. The stigma forms the distal portion of the style or stylodia. The stigma is composed of stigmatic papillae, the cells which are receptive to pollen. These may be restricted to the apex of the style or, especially in wind pollinated species, cover a wide surface.[2]

The stigma receives pollen and it is on the stigma that the pollen grain germinates. Often sticky, the stigma is adapted in various ways to catch and trap pollen with various hairs, flaps, or sculpturings.[3] The pollen may be captured from the air (wind-borne pollen, anemophily), from visiting insects or other animals (biotic pollination), or in rare cases from surrounding water (hydrophily). Stigma can vary from long and slender to globe shaped to feathery.[4]

Pollen is typically highly desiccated when it leaves an anther. Stigma have been shown to assist in the rehydration of pollen and in promoting germination of the pollen tube.[5] Stigma also ensure proper adhesion of the correct species of pollen. Stigma can play an active role in pollen discrimination and some self-incompatibility reactions, that reject pollen from the same or genetically similar plants, involve interaction between the stigma and the surface of the pollen grain.

Shape

The stigma is often split into lobes, e.g. trifid (three lobed), and may resemble the head of a pin (capitate), or come to a point (punctiform). The shape of the stigma may vary considerably:[2]

Cornsilk 7091
Corn stigma called "silk"
Stigma shapes (Capitate and simple)
Capitate and simple
Trifid Stigma
Trifid
Variations in style and stigma shape and size

Style

Structure

The style is a narrow upward extension of the ovary, connecting it to the stigmatic papillae. It may be absent in some plants in the case the stigma is referred to as sessile. Styles are generally tube-like—either long or short.[6] The style can be open (containing few or no cells in the central portion) with a central canal which may be filled with mucilage. Alternatively the style may be closed (densely packed with cells throughout). Most syncarpous monocots and some eudicots have open styles, while many syncarpous eudicots and grasses have closed (solid) styles containing specialised secretory transmitting tissue, linking the stigma to the centre of the ovary. This forms a nutrient rich tract for pollen tube growth.[4]

Where there are more than one carpel to the pistil, each may have a separate style-like stylodium, or share a common style. In Irises and others in the Iridaceae family, the style divides into three petal-like (petaloid) style branches (sometimes also referred to as 'stylodia'[7]), almost to the base of the style and is called tribrachiate.[8] These are flaps of tissue, running from the perianth tube above the sepal. The stigma is a rim or edge on the underside of the branch, near the end lobes.[9] Style branches also appear on Dietes, Pardanthopsis and most species of Moraea.[10]

In Crocuses, there are three divided style branches, creating a tube.[11] Hesperantha has a spreading style branch. Alternatively the style may be lobed rather than branched. Gladiolus has a bi-lobed style branch (bilobate). Freesia, Lapeirousia, Romulea, Savannosiphon and Watsonia have bifuracated (two branched) and recurved style branches.[10][2]

Iris versicolor 3
Iris versicolor showing three structures with two overlapping lips, an upper petaloid style branch and a lower tepal, enclosing a stamen
Iris missouriensis (3624887687)
Iris missouriensis showing the pale blue style branch above the drooping petal
Saffron stigmas Crocus speciosus corrected cropped
The feathery stigma of Crocus speciosus has branches corresponding to three carpels

Attachment to the ovary

Gynoecium morphology style position terminal
Terminal (apical)
Gynoecium morphology style position lateral
Lateral
Gynoecium morphology style position gynobasic
Gynobasic

May be terminal (apical), subapical, lateral, gynobasic, or subgynobasic. Terminal (apical) style position refers to attachment at the apex of the ovary and is the commonest pattern. In the subapical pattern the style arises to the side slightly below the apex. a lateral style arises from the side of the ovary and is found in Rosaceae. The gynobasic style arises from the base of the ovary, or between the ovary lobes and is characteristic of Boraginaceae. Subgynobasic styles characterise Allium.[12]

Pollination

Pollen tubes grow the length of the style to reach the ovules, and in some cases self-incompatibility reactions in the style prevent full growth of the pollen tubes. In some species, including Gasteria at least, the pollen tube is directed to the micropyle of the ovule by the style.[13]

See also

References

  1. ^ "stigma, n.". Oxford English Dictionary. Retrieved 30 March 2019. Under 6. Botany: "Plural usually stigmas."
  2. ^ a b c Dahlgren, Clifford & Yeo 1985, Gynoecium p. 11
  3. ^ The Penguin Dictionary of Botany, edited by Elizabeth Toothill, Penguin Books 1984 ISBN 0-14-051126-1
  4. ^ a b Rudall 2007.
  5. ^ Edlund, Swanson & Preuss 2004.
  6. ^ González & Arbo 2016, Estilo y estigma
  7. ^ Klaus Kubitzki (Editor) Flowering Plants. Dicotyledons: Celastrales, Oxalidales, Rosales, Cornales and Ericales, p. 208, at Google Books
  8. ^ Weberling 1989, pp. 182-186.
  9. ^ "The Anatomy Of Irises". herbs2000.com. Retrieved 27 July 2015.
  10. ^ a b Klaus Kubitzki (Editor) Flowering Plants. Monocotyledons: Lilianae (except Orchidaceae), p. 305, at Google Books
  11. ^ Michael Hickey, Clive King 100 Families of Flowering Plants, p. 562, at Google Books
  12. ^ Simpson 2011, Style position p. 378
  13. ^ Christophe Clement, Ettore Pacini, Jean-Claude Audran (Editors) Anther and Pollen: From Biology to Biotechnology, p. 151, at Google Books

Bibliography

External links

Corydalis filistipes

Corydalis filistipes is perennial flowering plant plant found only on Ulleung Island in North Gyeongsang Province, South Korea. It is listed as vulnerable on the IUCN Red List of Threatened Species. The grows to a height of 40 cm (16 in) and the tuber diameter reaches 3 cm (1.2 in) in diameter.

Iris hellenica

Iris hellenica is a species in the genus Iris, it is also in the subgenus of Iris. It is a rhizomatous perennial, from Saitas Mountain, in the Peloponnese Region of Greece. It has grey-green, sickle-shaped leaves, a tall slender stem, 2–3 white, lavender-blue, lilac or purple flowers and orange/purple beards. It was thought once to be a hybrid species of Iris germanica which also grows in the same area, before being separated into 2 species. It has only recently been published and is rarely cultivated as an ornamental plant in temperate regions.

Iris suaveolens

Iris suaveolens is a species in the genus Iris, it is also in the subgenus of Iris. It is a rhizomatous perennial, from Eastern Europe, ranging from the Balkans to Turkey (in Asia Minor). It has short, sickle shaped or curved, blue-green or greyish green leaves, a slender simple stem, with 1 or 2 fragrant spring blooming, flowers, between yellow and purple, with white or yellow beards. It was once known as Iris mellita (especially in parts of Europe), until that was re-classified as a synonym of Iris suaveolens. It is cultivated as an ornamental plant in temperate regions.

Petal

Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are usually accompanied by another set of special leaves called sepals, that collectively form the calyx and lie just beneath the corolla. The calyx and the corolla together make up the perianth. When the petals and sepals of a flower are difficult to distinguish, they are collectively called tepals. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa. Conversely, genera such as Rosa and Phaseolus have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly coloured tepals. Since they include Liliales, an alternative name is lilioid monocots.

Although petals are usually the most conspicuous parts of animal-pollinated flowers, wind-pollinated species, such as the grasses, either have very small petals or lack them entirely.

Stigma

Stigma or plural stigmata, stigmas may refer to:

Social stigma, the disapproval of a person based on physical or behavioral characteristics that distinguish them from others

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