Q.Give an account of the floral diagram of a flower.

The Floral Diagram

A floral diagram is a schematic, cross-sectional representation of a flower, drawn as if the flower were cut straight across and viewed from above. It shows the number of members in each floral whorl, whether those members are free or fused, and — importantly — how the parts of one whorl are arranged with respect to the parts of the whorls above and below it (for example, whether the petals alternate with the sepals, or whether the stamens are positioned opposite the petals or alternating with them). The diagram also shows the position of the mother axis (the stem or floral axis, conventionally drawn above the flower in the diagram) and the subtending bract, if present (conventionally drawn below the flower), because the orientation of the flower's parts is always described relative to these two reference points. By presenting the whole arrangement visually, a floral diagram communicates spatial relationships among floral parts — such as whether the ovary is superior or inferior, or how many locules it has — far more immediately than a written description could on its own, which is why it is included as a standard companion to every technical family description.

The Floral Formula

A floral formula condenses the same information into a single line of symbols, letters, and numbers, making it possible to represent a flower's structure in a compact, universally readable notation. Each floral whorl is represented by a standard letter: Br or a bract symbol for the bract, K for calyx (sepals), C for corolla (petals), P for perianth (used when calyx and corolla are not distinguishable, as in many monocots), A for androecium (stamens), and G for gynoecium (carpels). Following each letter, a number indicates how many members are present in that whorl; if the number is large or variable, the symbol for infinity may be used instead of a specific count.

Fusion within a whorl is shown by enclosing the number in brackets — for instance, K(5) indicates five sepals that are fused together (gamosepalous), while K5 without brackets would mean five free sepals (polysepalous). Fusion between different whorls (for example, stamens fused to the corolla tube) is shown by a curved line connecting the relevant symbols. The position of the ovary is shown by a line either above or below the G symbol: a line above indicates a superior ovary (hypogynous flower), and a line below indicates an inferior ovary (epigynous flower). The symmetry of the flower is shown by a symbol placed before the whorl symbols: a plus-shaped cross (⊕) indicates actinomorphic (radially symmetrical) flowers, while a symbol resembling a percent sign or an arrow indicates zygomorphic (bilaterally symmetrical) flowers. The sexuality of the flower is indicated by a female symbol, a male symbol, or both together for a bisexual flower.

Reading a Floral Formula

To read a floral formula, one works through it whorl by whorl in the fixed order Br, K, C (or P), A, G, noting for each the count, whether it is fused (bracketed) or free, and then checking the superior/inferior line under the G symbol and the symmetry and sexuality symbols placed at the start. For example, a formula showing an actinomorphic, bisexual flower with five fused sepals, five fused petals forming a rotate corolla, five stamens fused to the corolla tube, and a bicarpellary, syncarpous, superior ovary describes precisely the flower structure seen in family Solanaceae. Because the floral diagram and the floral formula both summarize the same underlying facts — one pictorially, the other symbolically — they are always presented together at the close of a family's technical description, giving both a visual and a shorthand-symbolic reference for the flower's structure.