Biol 324 Introduction to Seed Plant Taxonomy

Flower structure: the androecium

- A collective name for the stamens (male parts of the flower, which produce pollen)
- Parts of a stamen include the anther, filament, and connective (the connective is not
always apparent)
- Stamens usually have a single vein, but primitive leaf-like stamens (e.g. waterlilies), and
stamens in some monocots (e.g. banana family, Musaceae) have 3 main veins.

- Staminodes are sterile stamens (they do not produce pollen and usually don't have anthers).
- They may be vestigial or petal-like
- Penstemon has particularly bizarre staminodes (they resemble the style except that they are hairy at the tip).
- Petals may have originated as staminodes
- In some waterlilies there is a complete intergradation between petals, staminodes, and stamens
- In many double flowered mutants and cultivars, the extra petals are homeotically modified stamens.

Fusion (connation) of stamens
- Filaments may be connate but anthers free (not fused) as in many legumes.
- Anthers may be connate but the filaments are separate. This is called SYNGENESIOUS and is characteristic of the Asteraceae and some other families
- In syngenesious plants, the anthers shed their pollen inward (introrsely) and the style pushes up through the tube of anthers like a piston and shoves the pollen up to present it on top of the anthers.

Adnation of stamens
- stamens or lower part of filament may be fused to the petal (epipetalous stamens): especially common in sympetalous flowers
- In plants with a hypanthium, this represents adnation of part of the filaments with the bases of the petals and sepals.
- The style, stamen, and stigma are all adnate to form a structure called the COLUMN in orchid flowers.

Arrangement of stamens
- stamens are most commonly opposite the sepals (i.e. on the same radius as sepals), fitting the general pattern of alternation of whorls
- rarely, they can be opposite the petals. This is characteristic of some families such as Primulaceae, which are commonly OBDIPLOSTEMONOUS = having two whorls of stamens, the outer whorl being opposite the petals.

- Attachment: basifixed or versatile. Versatile anthers (e.g. Poaceae) are important in wind pollination
- Dehiscence by aperture: longitudinal or poricidal
- Dehiscence direction: introrse or extrorse. Introrse dehiscence (pollen shed inwards) is often found in self-pollinating flowers. Some species of Mitella (Saxifragaceae) differ in whether they have introrse or extrorse dehiscence, and it is related to the pollination system.

Adaptive evolution in stamens
- Differences in stamens are usually related to the pollination mechanism of the flower
- An example is the lever mechanism of Salvia (Lamiaceae). In some species only one anther sac is present and the connective is much enlarged. When a bee enters the flower, its head pushes up the sterile end of the connective, which lowers the fertile anther sac to deposit pollen on the bee's back.

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