Parts of a flower

Calyx: the sepals, usually green, which protect the flower in bud. They may be joined (gamosepalous) or free (polysepalous). Corolla: the petals, usually brightly coloured to attract insects for pollination; joined (gamopetalous) or free (polypetalous).

How sepals or petals overlap in the bud is aestivation:

• Valvate: edges just touch, without overlapping (Calotropis).
• Twisted: each petal overlaps the next one in a regular way, like a pinwheel (china rose, lady's finger, cotton).
• Imbricate: overlapping, but not in a regular direction (Cassia, gulmohur).
• Vexillary (papilionaceous): five petals of three kinds: the largest (standard) overlaps two side petals (wings), which overlap the two smallest front ones joined as the keel (pea, bean).

Androecium: the stamens. Each stamen is a stalk (filament) and a two-lobed anther holding pollen sacs. A sterile stamen is a staminode. Stamens may be joined to petals (epipetalous, brinjal) or to the perianth (epiphyllous, lily). They may be free (polyandrous) or joined by their filaments: in one bundle (monadelphous, china rose), two bundles (diadelphous, pea), or more than two (polyadelphous, citrus).

Gynoecium: the carpels. Each carpel has a stigma (receives pollen), a style (the stalk) and an ovary, which holds ovules attached to a cushion called the placenta. Carpels may be free (apocarpous, lotus, rose) or fused (syncarpous, mustard, tomato). After fertilisation, the ovules become seeds and the ovary becomes the fruit.

How ovules are arranged inside the ovary is placentation: marginal (along one edge, pea); axile (on a central axis, in chambers: china rose, tomato, lemon); parietal (on the inner wall; the ovary becomes two-chambered by a false septum: mustard, Argemone); free central (on a central column with no partitions: Dianthus, primrose); basal (at the base, often a single ovule: sunflower, marigold).