NEET Biology Notes Morphology of Flowering Plants Androecium
Androecium
Androecium
It represents a group of stamens or male reproductive organs. Each stamen consists of a long filament, anther and connective.
Dehiscence of Anthers
On the basis of dehiscence pattern anthers are generally of two types that is
- Extrorse When the anthers are opened towards the periphery side of a flower, then anthers are called extrorse. This process is helpful in cross pollination, e.g. poppy and Argemone.
Introrse When the anthers are opened towards the centre of a flower, the anthers are called introrse. This situation is quite common in bisexual flowers and helpful in cross pollination,
e.g. Citrus and Dianthus.
Types of Stamens
- Basifixed Filament adheres to the basal part of anther, e.g. Cassia and mustard.
- Adnate The filament runs through the connective, e.g. Michelia and Ranunculus.
- Dorsifixed The anther is fixed to the filament by its back and anther is immobile,
e.g. Citrus and Passiflora. - Versatile It is also a dorsifixed type attachment but here anther is free to swing over the filament,
e.g. Grasses, Eucalyptus and wheat. - When the stamen does not have anther the stamen is called staminode (sterile stamen).
Different conditions of stamens are as follows:
- Diplostemonous Condition
Here, two whorls of stamens are found. Stamens of outer whorl are alternate with petals, while the stamens of inner whorl are opposite to petals,
e.g. Murraya exotica and Cassia.
- Obdiplostemonous Condition
It is opposite condition of diplostemonous. Here, also occurs two whorls of stamens in which the outer whorl occurs opposite to petals and the inner whorl is alternate with petals,
e.g. Stellaria and Geranium.
- Epipetalous Condition
This condition arises when stamens are fused with petals (units of corolla which form second whorl of flower),
e.g. Solanaceae and Compositae families.
- Epiphyllous or Epitepalous Condition
In this, stamens become fused with tepals (units of perianth),
e.g. some members of Liliaceae as Asphodelus, Asparagus, etc.
- Gynandrous Condition
This situation arises when stamens are fused with the carpel (unit of gynoecium) throughout their whole length or by their anthers only,
e.g. Asclepiadaceae.
- Polyandrous Condition
In this condition, stamens are free (they are not attached with itself or with other floral parts),
e.g. mustard, Papavar, lily, radish, etc.
- Adelphous Condition
In this situation, filaments of anthers become fused but anthers remain free.
This situation may be of following types:
- Monoadelphous When ‘ll! filaments become fused and form a group, while anthers remain free, e.g. Malvaceae (China rose), Achyranthes, etc.
- Diadelphous When two separate bundles of united filaments (anthers are free) are formed, e.g. Papilionaceae (pea).
- Polyadelphous This condition arises when more than two separate bundles of filaments are formed (all anthers remain free),
e.g. castor (Ricinus), lemon [Citrus),
- Synandrous Condition
It is slightly different condition in which stamens are united throughout their whole length,
e.g. Cucurbitaceae (Cucurbita).
- Syngenesious or Synantherous Condition
Here, opposite condition of monoadelphous is seen, that is all anthers are united but their filaments remain free,
e.g. Compositae (sunflower).
Variation in Length of Stamen
On the basis of variation in length of stamen, these are of following types:
- Didynamous Here, total number of stamens are four, out of which two stamens are with shorter filaments, while rest two contain larger filaments,
e.g. Ocimum and Salvia. - Tetradynamous Here, total number of stamens are six, out of which four stamens of inner side have long filaments than the two stamens of outer side,
e.g. Cruciferae (mustard). - Some times stamens may form hair like or scale like structures called staminal corona,
e.g. Neiium.