Floral formula and Solanaceae

A semi-technical description is short, simple and scientific, and follows a fixed order: habit, then vegetative characters (root, stem, leaves), then floral characters (inflorescence, flower parts), then a floral diagram and a floral formula.

Floral formula symbols: Br bracteate, K calyx, C corolla, P perianth, A androecium, G gynoecium, ⊕ actinomorphic, % zygomorphic, ⚥ bisexual, ♂ male, ♀ female. A line under G means a superior ovary; a line over G means an inferior ovary.

Fusion within a whorl is shown by putting the number in brackets, e.g. C(5). Adhesion between whorls is shown by a line drawn over the symbols concerned, e.g. over C and A for epipetalous stamens.

A floral diagram shows the number of parts, their arrangement and their relation to one another. A dot at the top marks the mother axis; calyx is the outermost ring and gynoecium the centre.

The worked example (Figure 5.16) is mustard, family Brassicaceae: ⊕ ⚥ K2+2 C4 A2+4 G(2), ovary superior.

Solanaceae, the potato family, is a large family spread through the tropics, subtropics and temperate zones. Example figured: Solanum nigrum (makoi).

Vegetative: mostly herbs and shrubs, rarely small trees. Stem herbaceous (rarely woody); potato (Solanum tuberosum) has an underground stem. Leaves alternate and simple (rarely pinnately compound), without stipules (exstipulate), with reticulate venation.

Floral: inflorescence solitary, axillary or cymose; flower bisexual and actinomorphic; five united, persistent sepals and five united petals, both valvate; five epipetalous stamens; bicarpellary, obliquely placed, syncarpous, superior, bilocular ovary with a swollen placenta bearing many ovules (axile). Fruit berry or capsule; seeds many, endospermous.

Floral formula: ⊕ ⚥ K(5) C(5) A5 G(2), with a line joining C and A (epipetalous) and the ovary superior.

Uses: tomato, brinjal and potato are foods; chilli is a spice; belladonna and ashwagandha are medicines; tobacco is fumigatory; petunia is an ornamental.