Definitions

stamen

stamen

[stey-muhn]
stamen, one of the four basic parts of a flower. The stamen (microsporophyll), is often called the flower's male reproductive organ. It is typically located between the central pistil and the surrounding petals. A stamen consists of a slender stalk (the filament) tipped by a usually bilobed sac (the anther) in which microspores develop as pollen grains. The number of stamens is a factor in classifying plant families, e.g., there are 5 (or multiples of 5) in the rose family and 10 in the pulse family. In most flowers the stamens are constructed so as to promote cross-pollination and to avoid self-pollination; e.g., they may be longer than the pistil or may be so placed in relation to the pistil (as in the mountain laurel and the lady's-slipper) as to prevent the pollinating insect from transferring the pollen of a flower to its own pistil. There may be differing maturation times for the stigma of the pistil and for the anther. In some plants there are some flowers (staminate) that bear stamens and no pistil and others (pistillate) that have a pistil and no stamens; these flowers may be borne on the same or on separate plants of the same species. In some highly developed flowers, especially double ones, and in some horticultural varieties (e.g., the geranium) the stamen may be modified into a sterile petallike organ.

The stamen (plural stamina or stamens, from Latin stamen meaning "thread of the warp") is the male organ of a flower. Each stamen generally has a stalk called the filament (from Latin filum, meaning "thread"), and, on top of the filament, an anther (from Ancient Greek anthera, feminine of antheros "flowery," from anthos "flower"), and pollen sacs, called microsporangia. The development of the microsporangia and the contained haploid gametophytes, (called pollen-grains) is closely comparable with that of the microsporangia in gymnosperms or heterosporous ferns. The pollen is set free 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). It is then dropped, or carried by some external agent — wind, water or some member of the animal kingdom — onto the receptive surface of the carpel of the same or another flower, which is thus pollinated. Typical flowers have six stamens inside a perianth (the petals and sepals together), arranged in a whorl around the carpel (pistil). But in some species there are many more than six present in a flower (see, for example, the spider tree flower, below). Collectively, the stamens are called an androecium (from Greek andros oikia: man's house). They are positioned just below the gynoecium. The anthers are bilocular, i.e. they have two locules. Each locule contains a microsporangium. The tissue between the locules and the cells is called the connective.

In an immature, unopened flower bud, the filaments are still short. Their function is then to transport nutrients to the developing pollen. They start to lengthen once the bud opens. 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
  • synantherous : only the anthers are connate (such as in the Asteraceae)

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
  • tetradynamos : occurring as a set of six filaments with two shorter ones
  • exserted : extending beyond the corolla
  • included : not extending from the corolla.

Plant sexuality

In the typical flower (that is, the majority of flowering plant species) each flower has both a pistil and stamens. Bisexual plants are named hermaphrodites or perfect flowers.

In some species, however, the flowers are unisexual with only either male or female parts (monoecious = on the same plant; dioecious = on different plants). A flower with only male reproductive parts is called androecious. A flower with only female reproductive parts is called gynoecious.

A flower having only functional stamens is called a staminate flower.

An abortive or rudimentary stamen is called a staminodium, such as in Scrophularia nodosa.

The pistil and the 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.

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