The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium.[, p. 10]
Morphology and terminology
A stamen typically consists of a stalk called the
filament and an
anther which contains
sporangium. Most commonly, anthers are two-lobed (each lobe is termed a
locule) and are attached to the filament either at the base or in the middle area of the anther. The sterile (i.e. nonreproductive) tissue between the lobes is called the
connective, an extension of the filament containing conducting strands. It can be seen as an extension on the dorsal side of the anther. A
pollen grain develops from a
microspore in the microsporangium and contains the male
gametophyte. The size of anthers differs greatly, from a tiny fraction of a millimeter in
Wolfia spp up to five inches (13 centimeters) in
Canna iridiflora and
Strelitzia nicolai.
The stamens in a flower are collectively called the androecium. The androecium can consist of as few as one-half stamen (i.e. a single locule) as in Canna species or as many as 3,482 stamens which have been counted in the saguaro cactus ( Carnegiea gigantea).[Charles E. Bessey in SCIENCE Vol. 40 (November 6, 1914) p. 680.] The androecium in various species of plants forms a great variety of patterns, some of them highly complex.[Sattler, R. 1973. Organogenesis of Flowers. A Photographic Text-Atlas. University of Toronto Press. .][Sattler, R. 1988. A dynamic multidimensional approach to floral morphology. In: Leins, P., Tucker, S. C. and Endress, P. (eds) Aspects of Floral Development. J. Cramer, Berlin, pp. 1–6. ][Greyson, R. I. 1994. The Development of Flowers. Oxford University Press. .][Leins, P. and Erbar, C. 2010. Flower and Fruit. Schweizerbart Science Publishers, Stuttgart. .] It generally surrounds the gynoecium and is surrounded by the perianth. A few members of the family Triuridaceae, particularly Lacandonia schismatica and Lacandonia brasiliana,
Etymology
-
Stamen is the Latin word meaning "thread" (originally thread of the warp, in weaving).
-
Filament derives from classical Latin , meaning "thread"
[Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.]
-
Anther derives from French ,
[Klein, E. (1971). A comprehensive etymological dictionary of the English language. Dealing with the origin of words and their sense development thus illustration the history of civilization and culture. Amsterdam: Elsevier Science B.V.] from classical Latin , meaning "medicine extracted from the flower"[Siebenhaar, F.J. (1850). Terminologisches Wörterbuch der medicinischen Wissenschaften. (Zweite Auflage). Leipzig: Arnoldische Buchhandlung.][Saalfeld, G.A.E.A. (1884). Tensaurus Italograecus. Ausführliches historisch-kritisches Wörterbuch der Griechischen Lehn- und Fremdwörter im Lateinischen. Wien: Druck und Verlag von Carl Gerold's Sohn, Buchhändler der Kaiserl. Akademie der Wissenschaften.] in turn from Ancient Greek (),[Liddell, H.G. & Scott, R. (1940). A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford: Clarendon Press.] from
-
Androecium (: androecia) derives from Ancient Greek () meaning "man",
Variation in morphology
Depending on the species of plant, some or all of the stamens in a flower may be attached to the petals or to the
floral axis. They also may be free-standing or fused to one another in many different ways, including fusion of some but not all stamens. The filaments may be fused and the anthers free, or the filaments free and the anthers fused. Rather than there being two locules, one locule of a stamen may fail to develop, or alternatively the two locules may merge late in development to give a single locule.
[ pages 553–555] Extreme cases of stamen fusion occur in some species of
Cyclanthera in the family
Cucurbitaceae and in section
Cyclanthera of genus
Phyllanthus (family
Euphorbiaceae) where the stamens form a ring around the gynoecium, with a single locule.
Plants having a single stamen are referred to as "monandrous."
Pollen production
A typical anther contains four microsporangia. The
microsporangia form sacs or pockets (
locules) in the anther (anther sacs or pollen sacs). 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
Gametophyte called a
Pollen.
The pollen is eventually released when the anther forms openings (dehisces). These may consist of longitudinal slits, 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 Asclepiadoideae families, the pollen remains in masses called Pollinium, which are adapted to attach to particular pollinating agents such as birds or insects. More commonly, mature pollen grains separate and are dispensed by wind or water, pollinating insects, birds or other pollination vectors.
Pollen of must be transported to the stigma, the receptive surface of the carpel, of a compatible flower, for successful pollination to occur. After arriving, the pollen grain (an immature microgametophyte) typically completes its development. It may grow a pollen tube and undergo mitosis to produce two sperm nuclei.
Sexual reproduction in plants
In the typical flower (that is, in the majority of flowering plant species) each flower has both
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 pistil consists of one or more carpels. A flower with functional stamens but no functional pistil is called a staminate flower, or (inaccurately) a male flower. A flower with a functional pistil but no functional stamens is called a pistillate flower, or (inaccurately) a female flower.[ Encyclopædia Britannica.com]
An abortive or rudimentary stamen is called a staminodium or staminode, such as in Scrophularia.
The Gynoecium and stamens of are fused into a column.
Terminology
- Stamen
Stamens can also be
adnate (fused or joined from more than one whorl):
-
epipetalous: adnate to the corolla
-
epiphyllous: adnate to undifferentiated (as in many Liliaceae)
They can have different lengths from each other:
-
didymous: two equal pairs
-
didynamous: occurring in two pairs, a long pair and a shorter pair
-
tetradynamous: occurring as a set of six stamens with four long and two shorter ones
or respective to the rest of the flower (
perianth):
-
exserted: extending beyond the corolla
-
included: not extending beyond the corolla
They may be arranged in one of two different patterns:
-
spiral; or
-
whorled: one or more discrete whorls (series)
They may be arranged, with respect to the
petals:
-
diplostemonous: in two whorls, the outer alternating with the petals, while the inner is opposite the petals.
-
haplostemenous: having a single series of stamens, equal in number to the proper number of petals and alternating with them
-
obdiplostemonous: in two whorls, with twice the number of stamens as petals, the outer opposite the petals, inner opposite the sepals, e.g. Simaroubaceae ( see diagram)
- Connective
Where the connective is very small, or imperceptible, the anther lobes are close together, and the connective is referred to as
discrete, e.g.
Euphorbia pp.,
Adhatoda zeylanica. Where the connective separates the anther lobes, it is called
divaricate, e.g.
Tilia,
Justicia gendarussa. The connective may also be a long and stalk-like, crosswise on the filament, this is a
distractile connective, e.g.
Salvia. The connective may also bear appendages, and is called
appendiculate, e.g.
Nerium odorum and some other species of
Apocynaceae. In
Nerium, the appendages are united as a staminal corona.
- Filament
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) as follows:
- Anther
Anther shapes are variously described by terms such as
linear,
rounded,
sagittate,
sinuous, or
reniform.
The anther can be attached to the filament's connective in two ways:
-
basifixed: attached at its base to the filament
-
pseudobasifixed: a somewhat misnomer configuration where connective tissue extends in a tube around the filament tip
-
dorsifixed: attached at its center to the filament, usually versatile (able to move)
Gallery
Bibliography
External links
