General description:-
A diverse family of herbs, shrubs, trees and climbers. British wild representatives are predominantly herbs, recognised by opposite leaves with stipules, often appearing whorled, united petals and an inferior ovary. This sheet emphasises the British herbaceous genera.
Characteristics:-
1) Habit, annual or perennial in the principal British herbaceous genera; woody forms are especially diverse in the tropics.
2) Stems, often four-angled in British herbs; surfaces glabrous, softly hairy or furnished with backward-pointing prickles.
3) Cauline, usually opposite, with stipules between the paired leaves;
a) blade, simple, usually entire, sessile or petiolate.
b) stipules, commonly enlarged and leaf-like in British genera, producing apparent whorls of 4 or more members.
Flowers:-
1) Inflorescences, terminal or axillary cymes, sometimes assembled into panicles or compact heads.
2) Bracts, small or conspicuous; involucral bracts surround the flower heads in some genera.
3) Flowers, usually bisexual and radially symmetrical; unisexual flowers occur in some taxa.
4) Calyx, usually with united sepals, but its free limb is minute or absent in many British genera.
5) Corolla, petals united, commonly with 4 or 5 lobes; rotate, tubular, funnel-shaped or otherwise variable.
6) Stamens, usually equal in number to the corolla lobes and alternating with them;
a) filaments, attached to the corolla tube.
b) anthers, generally 2-celled, opening longitudinally.
7) Ovary, normally inferior, formed from united carpels and usually 2-celled;
a) style, usually single below, with divided or undivided stigmatic regions; often 2-branched in British herbs.
8) Ovules, one per locule in the familiar British bedstraw group, but one to many across the family.
Fruit and seeds:-
1) Fruit, commonly a dry schizocarp dividing into 2 one-seeded mericarps in British herbs; capsules, berries and drupes occur elsewhere in the family.
2) Mericarps, smooth, granular, hairy or furnished with hooked bristles; their surface is often diagnostic. Rubia has fleshy fruits.
Recognition:-
Opposite leaves with interpetiolar stipules, a sympetalous corolla and an inferior ovary provide the principal family combination. In British herbs, apparent leaf whorls and paired one-seeded fruit units are especially useful.
Genera relevant to catalogue:-
Asperula: flowers with a distinct corolla tube; Asperula arvensis has compact blue-flowered heads, whereas Asperula cynanchica has pale flowers in branched cymes.
Cruciata: leaves in apparent whorls of 4; Cruciata laevipes has small axillary yellow flower clusters and softly hairy stems.
Galium: corolla usually rotate with a very short tube; inflorescence, leaf arrangement and mature fruit surface help distinguish species.
Sherardia: small terminal flower heads, a tubular pinkish corolla and conspicuous persistent calyx teeth.
Rubia: scrambling plants with recurved prickles and fleshy fruits.
Taxonomic note:-
Rubiaceae belongs to Gentianales. The requested Asperula names are retained in this catalogue; some modern treatments place Asperula cynanchica in Cynanchica. This does not alter its family placement.