What is a flower? Describe the parts of a typical angiosperm flower.

(N/A) flower is defined as the reproductive unit of an angiosperm,specialized for sexual reproduction.
$A$ typical flower consists of four distinct whorls arranged on a condensed axis called the thalamus:
$(A)$ Calyx: The outermost whorl consisting of sepals. They are typically green and protect the flower in the bud stage. If sepals are free,it is polysepalous; if fused,it is gamosepalous.
$(B)$ Corolla: The second whorl consisting of petals. They are often brightly colored to attract pollinators. If petals are free,it is polypetalous; if fused,it is gamopetalous.
$(C)$ Androecium: The male reproductive whorl consisting of stamens. Each stamen has a filament and a bilobed anther,where pollen grains are produced via meiosis.
$(D)$ Gynoecium: The innermost female reproductive whorl consisting of one or more carpels. Each carpel comprises an ovary at the base,a style (tube),and a stigma (receptive surface). The ovary contains ovules attached to the placenta.