Herbs or small shrubs. Leaves exstipulate, simple, entire. Inflorescence cymose. Flowers 4- or 5-merous, actinomorphic. Sepals free; petals usually free (sometimes joined at base); fertile stamens in one whorl, sometimes with a whorl of staminodes. Ovary superior, usually 8- or 10-celled. Styles usually free. Fruit a loculicidal capsule; seeds usually 1 in each loculus.
1) Flowers 5-merous; seeds flat.
LINUM
Herbs or small shrubs. Leaves sessile, usually narrow, 1-veined or parallel-veined. Flowers 5-merous. Sepals entire. Petals clawed, longer than the sepals. Stamens 5, alternating with 5 tooth-like staminodes; filaments united at base. Capsule dehiscing with 10 valves, often with a short beak. Seeds flat.
1) Flowers 5-merous; seeds flat.
Measurements of the capsule exclude the beak. Pedicel characters refer to the mature fruiting stage. The inflorescence is basically cymose, but in many species (Sect. Dasylinum, Linastrum and Linum) well-developed inflorescences have branches which are pseudoracemose (cincinni). The difference between an irregular dichasium and an inflorescence composed of cincinni seems to be at least in part a question of individual development, and is not therefore of great taxonomic importance.
Sect. DASYLINUM
Leaves:- Alternate, pubescent without basal glands.
Flowers:- Sepals glandular-ciliate. Petals free, blue or pink. Stigmas linear. With stamens and styles at different levels in flowers on different plants of the same species (heterostylous).
Sect. LINASTRUM
Leaves:- Mostly alternate, glabrous, without basal glands.
Flowers:- Sepals glandular-ciliate. Petals free, yellow, pink or white. Stigmas linear or pin-headed (capitate), rarely club-shaped (clavate).Stamens and styles uniformly positioned (homostylous) or at different levels (heterostylous).
Sect. LINUM
Leaves:- Alternate, glabrous, without basal glands.
Flowers:- Sepals eglandular. Petals free, blue, purple or pink. Stigmas pin-headed (capitate), club-shaped (clavate) or linear. Stamens and styles uniformly positioned (homostylous) or at different levels (heterostylous).
SECT. SYLLINUM. Includes the species, L. arboreum, L. nodiflorum.
Stem with narrow wings decurrent from leaf-bases. Leaves alternate, with a pair of glands at base. Sepals sometimes glandular-ciliate. Petals slightly joined at base of claw, usually yellow. Stigmas usually linear or oblong-linear. Homostylous or heterostylous.
RADIOLA
General description:- Herbs or small shrubs.
Leaves:- Sessile, usually narrow, 1-veined or parallel-veined.
Flowers:- 4-merous. sepals toothed at the apex. Petals more or less equalling the sepals. Stamens 5, alternating with 5 tooth-like staminodes; filaments united at the base.
Fruit:- capsule dehiscing with 8 valves; seeds ovoid.
Key features:-
1) Flowers 4-merous.
2) Seeds ovoid.