Stamens are the male reproductive organs of flowers. Typically, a stamen is made up of a pollen‐producing anther borne on a filament. Pollen arises in four sporogenous regions within the anther. The sporogenous cells are surrounded by nutritive support cells, the tapetum. Mature pollen is released from the anther by dehiscence of the anther wall. The developmental identity of the stamen is conferred by the combined action of MADS transcription factors. Subsequent cellular differentiation is under the control of a cascade of other transcription factor and signalling genes now being identified. Male sterility is useful in plant breeding, and may arise by loss‐of‐function of these genes, as well as by defects in mitochondria (cytoplasmic male sterility). Differences in the structure of stamens are associated with the types of pollinators involved. Stamens evolved from the microsporangia‐bearing organs of early seed plants.

Key Concepts:

  • Pollen is generated in stamens, the male reproductive organs of flowers.

  • Pollen arises from sporogenous cells within the anthers.

  • Sporogenous cells are surrounded by the tapetum, a nutritive layer of support cells.

  • Stamen identity is conferred by the action of MADS transcription factors controlling B, C and SEPALLATA function.

  • The transcription factor SPOROCYTELESS is required for generation of the sporogenous cells.

  • Other transcription factors and signalling kinases are required for the entire developmental cascade and are now being identified.

  • Mature pollen is released by dehiscence of the anther wall through slits called stomia.

  • The structure of stamens in a species is closely adapted to the specific pollinators involved for that species.

  • Pollen is also generated in nonflowering seed plants (gymnosperms and various extinct lineages), but it arises in leaf‐like organs (microsporophylls) rather than stamens.

Keywords: anther; cytoplasmic male sterility; dehiscence; pollen; pollination syndrome; tapetum

Figure 1.

Diagram of a typical stamen (e.g. the true lily, Lilium (Liliaceae)) at a stage when the pollen is maturing (after meiosis and before dehiscence). The stamen is made up of an anther (green) and a filament (white). The internal structure of the anther is shown in a transverse section. There are two thecae, each with two pollen sacs, separated by a connective (pale green). A vascular strand is present within the connective. Tissues within each pollen sac are, from the outside, the epidermis (dark yellow), a late‐forming endothecium with lignified thickening (orange), a middle layer (pale green), the nutritive tapetum (pink) and developing pollen grains (pale yellow). When pollen is mature, the two pollen sacs on each side will join and each theca will dehisce along a weakened region of the endothecium, the stomium.

Figure 2.

Developmental pathway leading to the generation of microspores and surrounding vegetative cells in a pollen sac of the anther. Archesporial cells arise between the outer epidermis and internal, undifferentiated cortical cells. The archesporial cells divide several times to generate outer primary parietal cells, and inner sporogenous cells that, in turn divide to generate secondary parietal cells and pollen mother cells, respectively. Meiosis occurs in the pollen mother cells (also known as microsporocytes), yielding microspores which separate and develop into pollen grains. The parietal cells differentiate into a layer of tapetal cells which envelops the spore cells providing nutrient and, later, components of the pollen wall. The parietal cells also generate an outer layer of endothecial cells which lie under the epidermis, and which are involved in anther dehiscence to release the mature pollen. An undifferentiated middle layer lies between the tapetum and endothecium. Several key Arabidopsis genes involved in controlling specific steps of cellular specialization are shown in red (see text). AG, AGAMOUS; BAM, BARELY ANY MERISTEM; DYT1, DYSFUNCTIONAL TAPETUM1; EMS1, EXCESS MICROSPOROCYTES1; SPL, SPOROCYTELESS and TPD1, TAPETAL DETERMINANT1.

Figure 3.

Flowers of Eucalyptus (Corymbia) ficifolia (Myrtaceae), each with many pigmented stamens that act to attract pollinators. Pigment is localized to the long filaments, each of which is capped by a tiny anther. The perianth (petals and sepals) occurs as a cap (buds on right) that falls off as the buds open.



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Smyth, David R(Jan 2010) Stamens. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002066.pub2]