Stamen
Encyclopedia
The stamen is the pollen producing reproductive organ
of a flower
. Stamens typically consist of a stalk called the filament (from Latin filum, meaning "thread"), and an anther (from Ancient Greek
anthera, feminine of antheros "flowery," from anthos "flower"), which contains microsporangia
. Anthers are most commonly two-lobed and are attached to the filament either at the base or in the middle portion. The sterile tissue between the lobes is called the connective.
A typical anther contains four microsporangia. The microsporangia form sacs or pockets (locules) in the anther. The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called the tapetum and initially contains diploid pollen mother cells. These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis. Each microspore then divides mitotically to form an immature microgametophyte
called a pollen grain
.
The pollen is eventually released by the opening (dehiscence) of the anther, generally by means of longitudinal slits, but sometimes by pores, as in the heath
family (Ericaceae
), or by valves, as in the barberry family (Berberidaceae
). In some plants, notably members of the Orchidaceae
and the Asclepiadoideae, the pollen remains in masses called pollinia
, usually specialised in ways adapted to being carried by particular pollinating agents such as birds or large insects. More commonly, mature pollen grains separate and are dispensed in ways suitable for wind or water transport, or for dusting onto pollinating insects, whether large or small.
When ready, the pollen is carried by some external agent (wind, water or some member of the animal kingdom
) to the receptive surface of the carpel
of the same or another flower. This process is known as pollination
. After successful pollination, the pollen grain (immature microgametophyte) completes its development by growing a pollen tube and undergoing mitosis to produce two male gametes (sperm).
The stamens in a flower are collectively called the androecium (from Greek
andros oikia: man's house). The androecium forms a whorl surrounding the gynoecium
(carpels) and inside the perianth (the petal
s and sepal
s together) if there is one. (The one exception is a few members of the family Triuridaceae
, particularly Lacandonia schismatica, in which the gynoecium surrounds the androecium.)
Stamens can be free or fused in various ways. A column formed from the fusion of multiple filaments is known as an androphore.
Stamens can be connate (fused or joined in the same whorl):
Stamens can also be adnate (fused or joined from more than one whorl):
In the typical flower (that is, in the majority of flowering plant species) each flower has both carpels
and stamens. In some species, however, the flowers are unisexual with only carpels or stamens. (monoecious = both types of flowers found on the same plant; dioecious
= the two types of flower found only on different plants). A flower with only stamens is called androecious. A flower with only carpels is called gynoecious.
A flower having only functional stamens and lacking functional carpels is called a staminate flower, or (inaccurately) male. A plant with only functional carpels is called pistillate, or (inaccurately) female.
An abortive or rudimentary stamen is called a staminodium or staminode, such as in Scrophularia nodosa
.
The carpels
and stamens of orchids are fused into a column
. The top part of the column is formed by the anther. This is covered by an anther cap.
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
of a flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
. Stamens typically consist of a stalk called the filament (from Latin filum, meaning "thread"), and an anther (from Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
anthera, feminine of antheros "flowery," from anthos "flower"), which contains microsporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
. Anthers are most commonly two-lobed and are attached to the filament either at the base or in the middle portion. The sterile tissue between the lobes is called the connective.
A typical anther contains four microsporangia. The microsporangia form sacs or pockets (locules) in the anther. The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called the tapetum and initially contains diploid pollen mother cells. These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis. Each microspore then divides mitotically to form an immature microgametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
called a pollen grain
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
.
The pollen is eventually released by the opening (dehiscence) of the anther, generally by means of longitudinal slits, but sometimes by pores, as in the heath
Erica
Erica ,the heaths or heathers, is a genus of approximately 860 species of flowering plants in the family Ericaceae. The English common names "heath" and "heather" are shared by some closely related genera of similar appearance....
family (Ericaceae
Ericaceae
The Ericaceae, commonly known as the heath or heather family, is a group of mostly calcifuge flowering plants. The family is large, with roughly 4000 species spread across 126 genera, making it the 14th most speciose family of flowering plants...
), or by valves, as in the barberry family (Berberidaceae
Berberidaceae
Berberidaceae are a family of 15 genera flowering plants commonly called the barberry family. This family is in the order Ranunculales. The family contains about 570 species, of which the majority are in Berberis...
). In some plants, notably members of the Orchidaceae
Orchidaceae
The Orchidaceae, commonly referred to as the orchid family, is a morphologically diverse and widespread family of monocots in the order Asparagales. Along with the Asteraceae, it is one of the two largest families of flowering plants, with between 21,950 and 26,049 currently accepted species,...
and the Asclepiadoideae, the pollen remains in masses called pollinia
Pollinium
Pollinium, or plural pollinia, is a coherent mass of pollen grains in a plant.They are the product of only one anther, but are transferred, during pollination, as a single unit. This is regularly seen in plants such as orchids and many species of milkweeds .Most orchids have waxy pollinia...
, usually specialised in ways adapted to being carried by particular pollinating agents such as birds or large insects. More commonly, mature pollen grains separate and are dispensed in ways suitable for wind or water transport, or for dusting onto pollinating insects, whether large or small.
When ready, the pollen is carried by some external agent (wind, water or some member of the animal kingdom
Kingdom (biology)
In biology, kingdom is a taxonomic rank, which is either the highest rank or in the more recent three-domain system, the rank below domain. Kingdoms are divided into smaller groups called phyla or divisions in botany...
) to the receptive surface of the carpel
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
of the same or another flower. This process is known as pollination
Pollination
Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...
. After successful pollination, the pollen grain (immature microgametophyte) completes its development by growing a pollen tube and undergoing mitosis to produce two male gametes (sperm).
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
andros oikia: man's house). The androecium forms a whorl surrounding the gynoecium
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
(carpels) and inside the perianth (the petal
Petal
Petals are modified leaves that surround the reproductive parts of flowers. They often are 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 lying...
s and sepal
Sepal
A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...
s together) if there is one. (The one exception is a few members of the family Triuridaceae
Triuridaceae
Triuridaceae is a family of flowering plants. Such a family has been recognized by relatively few taxonomists.The APG II system, of 2003, does recognize such a family and places it in the order Pandanales, in the clade monocots...
, particularly Lacandonia schismatica, in which the gynoecium surrounds the androecium.)
Stamens can be free or fused in various ways. A column formed from the fusion of multiple filaments is known as an androphore.
Descriptive terms
The anther can be attached to the filament in two ways:- basifixed: attached at its base to the filament; this gives rise to a longitudinal dehiscence (opening along its length to release pollen)
- versatile: attached at its center to the filament; pollen is then released through pores (poricidal dehiscence).
Stamens can be connate (fused or joined in the same whorl):
- monadelphous: fused into a single, compound structure
- diadelphous: joined partially into two androecial structures
- synandrous: only the anthers are connate (such as in the AsteraceaeAsteraceaeThe Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
)
Stamens can also be adnate (fused or joined from more than one whorl):
- epipetalous: adnate to the corolla
- didynamous: occurring in two pairs of different length
- tetradynamous: occurring as a set of six filaments with two shorter ones
- exserted: extending beyond the corolla
- included: not extending from the corolla.
Sexual reproduction in plants
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
and stamens. In some species, however, the flowers are unisexual with only carpels or stamens. (monoecious = both types of flowers found on the same plant; dioecious
Dioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...
= the two types of flower found only on different plants). A flower with only stamens is called androecious. A flower with only carpels is called gynoecious.
A flower having only functional stamens and lacking functional carpels is called a staminate flower, or (inaccurately) male. A plant with only functional carpels is called pistillate, or (inaccurately) female.
An abortive or rudimentary stamen is called a staminodium or staminode, such as in Scrophularia nodosa
Scrophularia
The genus Scrophularia of the family Scrophulariaceae comprises about 200 species of herbaceous flowering plants commonly known as figworts. Species of Scrophularia all share square stems, opposite leaves and open two-lipped flowers forming clusters at the end of their stems...
.
The carpels
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
and stamens of orchids are fused into a column
Column (botany)
The column, or technically the gynostemium, is a reproductive structure that can be found in several plant families: Aristolochiaceae, Orchidaceae, and Stylidiaceae....
. The top part of the column is formed by the anther. This is covered by an anther cap.