Excluding Ctenolophacaceae, Erythroxylaceae, Hugoniaceae, Lepidobotryaceae
Habit and leaf form. Herbs and shrubs (mostly), or trees (a few). Mesophytic, or xerophytic. Leaves alternate to opposite; usually spiral; sessile; non-sheathing; simple. Lamina entire. Leaves stipulate, or exstipulate. Stipules small, sometimes represented by glands; caducous. Lamina margins entire. Leaves without a persistent basal meristem.
Leaf anatomy. Mucilaginous epidermis present, or absent. Stomata present; commonly paracytic.
Lamina dorsiventral. The mesophyll with sclerencymatous idioblasts, or without sclerenchymatous idioblasts. Minor leaf veins with phloem transfer cells (Linum), or without phloem transfer cells (Linum, Radiola).
Stem anatomy. Nodes tri-lacunar. Secondary thickening developing from a conventional cambial ring. Xylem with tracheids; with fibre tracheids, or without fibre tracheids; with vessels. Vessel end-walls simple. Vessels without vestured pits. Wood parenchyma apotracheal, or paratracheal, or apotracheal and paratracheal (often difficult to classify).
Reproductive type, pollination. Hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in `inflorescences'; in cymes. The terminal inflorescence unit cymose. Inflorescences cincinni or dichasia, sometimes pseudoracemose. Flowers regular; usually 5 merous; cyclic. Free hypanthium absent. Hypogynous disk present (outside the androecium); extrastaminal; of separate members, or annular.
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous, or gamosepalous (sometimes basally connate); persistent; imbricate (quincuncial); with the odd member posterior. Corolla 5; 1 whorled; polypetalous, or gamopetalous; imbricate, or contorted; regular. Petals clawed (often), or sessile.
Androecium 5, or 10, or 15 (rarely). Androecial members free of the perianth; all equal, or markedly unequal; coherent (basally, into a ring); 1 - adelphous. Androecium exclusively of fertile stamens, or including staminodes (often). Staminodes sometimes 5 (alternating with the fertile stamens). Stamens 5, or 10, or 15; isomerous with the perianth, or diplostemonous to triplostemonous; alternisepalous, or oppositisepalous. Anthers dehiscing via longitudinal slits; introrse; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with one middle layer, or initially with more than one middle layer; of the `monocot' type. Tapetum glandular. Pollen grains aperturate, or nonaperturate (e.g. Reinwardtia); 3 - aperturate, or 4-20 - aperturate (?); colpate, or porate, or rugate (rarely), or colporate (variously tricolpate or colporate, polycolpate, or multiporate); 3-celled.
Gynoecium 2-3-5; syncarpous; synovarious to synstylovarious; superior. Ovary 1 locular (apically only, when the placentas fall short), or 2-3-5 locular, or 4-10 locular (because of extra projections from the carpel midribs which, however, do not reach the central column). Gynoecium stylate. Styles 1, or 3-5; free to partially joined; apical. Stigmas dry type; papillate; Group II type. Placentation axile. Ovules 2 per locule; pendulous; non-arillate; anatropous; bitegmic; tenuinucellate, or crassinucellate. Outer integument not contributing to the micropyle. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed, or not formed (the three nuclei remaining naked in Linum); 3; not proliferating; ephemeral. Synergids hooked (sometimes with filiform apparatus). Endosperm formation nuclear, or helobial. Endosperm haustoria present; chalazal. Embryogeny solanad.
Fruit fleshy, or non-fleshy; dehiscent, or indehiscent, or a schizocarp; when schizocarpic, comprising mericarps (two mericarps, in Anisadenia); when non-schizocarpic a capsule, or a drupe, or a nut. Capsules septicidal. Seeds endospermic, or non-endospermic; with amyloid, or without amyloid. Cotyledons 2. Embryo chlorophyllous (11 species of Linum); straight.
Seedling. Germination phanerocotylar.
Physiology, biochemistry. Cyanogenic, or not cyanogenic. Cynogenic constituents of Hegnauer's `Group C'. Alkaloids absent (4 species). Iridoids absent. Proanthocyanidins absent. Flavonols absent. Ellagic acid absent (2 genera, 3 species). Saponins/sapogenins absent. Aluminium accumulation not found. C3. C3 recorded in Linum. Anatomy non-C4 type (Linum).
Geography, cytology. Frigid zone to tropical. Cosmopolitan. X = 6-11(+).
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren's Superorder Rutiflorae; Geraniales. Cronquist's Subclass Rosidae; Linales. Takhtajan's Subclass Rosidae; Rutanae; Geraniales. Species 90. Genera 8; Anisadenia, Cliococca, Hesperolinon, Linum, Radiola, Reinwardtia, Sclerolinon, Tirpitzia.
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