The androecium is the male reproductive organ of the flower, made up of the set of stamens, also called microphiles. In fact, stamens are the flower structure of flowering plants where pollen is generated.
The stamens of angiosperms are made up of a filament that ends in four pollen sacs or sporangia grouped in pairs. Each pair of sporangia forms a teak, and the two teak in the stamen constitute the anther.
Stamens. Source: flickr.com
The thecas are located on each flank of the insertion point of the filament, joined together by a connective tissue. These structures show great variability, becoming linear, oblong, globose or ovoid, and with yellowish, bluish and reddish tones.
Inside the pollen sacs, the process of microsporogenesis occurs, giving rise to pollen grains or microgametophytes. Inside the pollen grains the male gametes or sperm cells that act in the pollination process develop.
characteristics
Of the floral whorls, the androecium together with the calyx, corolla and gynoecium are the elements that make up the flower. The androecium is made up of three appendages located on the same axis or longitudinal plane.
The androecium is made up of male stamens or organs, which in turn are made up of the filament and anthers. The filament is a sterile structure that supports the anthers at its end, where the pollen that contains the male gametes of the flower is formed.
The filament allows the union of the flower to the stem, it is differentiated by an epidermis with a high content of cutin, and presents various trichomes and stomata. The inner part of the filament is made up of a parenchyma of vacuolized cells through which a vascular bundle passes.
The filament is a variable structure depending on each floral species, being short, relatively long or sessile. They are regularly filiform, thick or petaloid, and are usually provided with terminal appendages.
The anthers are located at the upper end of the filament, and constitute the fertile structure of the androecium. Each anther is made up of a pair of teak, formed in turn by two pollen sacs where spores are produced.
Anthers Source: flickr.com
When the male gametes contained within the pollen have matured, the anther opens through a phenomenon called dehiscence. Dehiscence occurs in different ways, longitudinal or transverse, and is subject to the functionality of the endothecium.
In the floral structure, the androecium generally surrounds the gynoecium or female apparatus composed of carpels. In addition, it is located on the perianth or set of floral leaves that constitute the flower's covering.
On the other hand, the androecium has different shapes and sizes, being shorter or longer than the perianth. Hiding or protruding from the floral structure, the arrangement of the whorls also depends on each floral species.
Classification
The classification of the androecium can be made based on the length of the stamens and the arrangement of the androecium in relation to the floral structures. On the other hand, it can be differentiated in relation to the position of the anther and the opening or dehiscence of the anthers.
Based on the length of the stamens, androecium can be classified into:
- Androecium didynamo: the pairs of stamens are of variable length.
- Androceo tetradínamo: typical of the cruciferous, formed by six stamens of which two are longer than the rest.
Regarding the arrangement of the androecium with respect to the other floral structures, it is classified as:
- Even: the stamens do not reach the height of the corolla.
- Epipetal: the stamens are born directly from the petals of the corolla.
- Exerts: the anthers at the end of the stamens exceed the corolla.
The classification of the androecium based on the position of the anther on the outer filament:
- Adnatas: the anthers are inserted into the structure of the filament.
- Apicifijas: the anther joins the end of the filament through its apical part.
- Basifijas: the anther is fixed from its basal position to the end of the filament.
- Dorsifixes: Also called medixes, the filament joins the middle of the anther.
- Versatile: they are of the dosed type, where the end of the filament is attached to a dorsal point of the anther.
According to the opening of the anther or dehiscence, the following are distinguished:
- Longitudinal: the opening of the anther occurs along each teak.
- Transversal: the opening of the anther occurs in a transverse line in each teak.
- Poricidal: also called foraminal, the opening occurs through pores.
- Valvar: the anther detaches one side of its valve-shaped structure, shedding pollen.
Hibiscus filament. Source: flickr.com
Types of androecium
The classification of various plant species is subject to the shape of the androecium. Generally the stamens are presented in a free form, but the degree of fusion allows differentiating families of great economic importance.
In this case, according to the degree of fusion, the following types of androecium can be found:
- Androecium monodelph: characteristic of malvaceae. The filaments are completely united, forming a layer that covers the style of the flower.
- Androceo diadelfo: typical of legumes. The filaments are held together in a pair.
- Synandry: the filaments and anthers fuse to form a compact structure. Common of cucurbits.
- Syngenesis: it is a special case, where the anthers are the structures that remain together. Also called sinanteria, it is a common compound.
Function
The primary function of the androecium is the production of the pollen grains that contain the male gametes. Pollen is produced through the process of microsporogenesis inside pollen sacs.
A functional anther is formed by diploid stem cells (2n) from the sporophyte that will give rise to the microspores. These cells divide by meiosis to produce four meiospores (n), which are monocucleate pollen grains or microspores.
Inside each pollen sac, numerous meiospores are formed, which once mature can spread independently. In some species, pollen grains disperse as a single group or pollinia. Once the microspores are formed, microsporogenesis ends.
References
-
- Androecium. (2018) Wikipedia, The Free Encyclopedia. Recovered at: wikipedia.org
- Megias Manuel, Molist Pilar & Pombal Manuel A. (2018) Plant Organs. Flower. Atlas of Plant and Animal Histology. Faculty of Biology. University of Vigo.
- Menéndez Valderrey, JL (2018) The androecium: the stamens. Nº 381. ISSN 1887-5068. Recovered at: asturnatura.com
- Popoff Orlando Fabián (2018) Morphology of Vascular Plants. Item 4. The flower. Hypertexts of Morphological Botany. 26 pp.