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The families of flowering plants.                                                                                                                                                                

Linaceae S.F. Gray

                        

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ExcludingCtenolophacaceae, Erythroxylaceae, Hugoniaceae, Lepidobotryaceae

Habit and leaf form. Herbs and shrubs (mostly), or trees (a few); non-laticiferous and without coloured juice. ‘Normal’ plants. Mesophytic, or xerophytic. Leaves alternate to opposite; usually spiral; sessile; non-sheathing; simple. Laminaentire. 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. The cortex containing cristarque cells, or without cristarque cells. 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. Fertile flowershermaphrodite. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence unit cymose. Inflorescences cincinni or dichasia, sometimes pseudoracemose. Flowersregular; usually 5 merous; cyclic. Free hypanthium absent. Hypogynous disk present (outside the androecium); extrastaminal; of separate members, or annular.

Perianthwith distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous, or gamosepalous (sometimes basally connate). Calyx lobes markedly longer than the tube. Calyx persistent; imbricate (quincuncial); with the median 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); in the same series as the fertile stamens, or internal to the fertile stamens (?). Stamens 5, or 10, or 15; isomerous with the perianth, or diplostemonous to triplostemonous; alternisepalous, or oppositisepalous (mostly). 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 carpelled. The pistil 2–10 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary1 locular (apically only, when the placentas fall short), or 2–3–5 locular (but sometimes exhibiting extra projections from the carpel midribs which, however, do not reach the central column). Locules partially secondarily divided by ‘false septa’, or without ‘false septa’. 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; epitropous (Engler); 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. Mericarps when schizocarpic, 2 (in Anisadenia); one-seeded. Fruit 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; flat. 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 not detected. Proanthocyanidins absent. Flavonols absent. Ellagic acid absent (2 genera, 3 species). Saponins/sapogenins absent. Aluminium accumulation not found. Sugars transported as sucrose, or as oligosaccharides + sucrose, or as sugar alcohols + oligosaccharides + sucrose (?). C3. C3 physiology recorded directly 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. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Malpighiales.

Species 90. Genera 8; Anisadenia, Cliococca, Hesperolinon, Linum,Radiola, Reinwardtia, Sclerolinon, Tirpitzia.

 Illustrations:

  • Technical details: Linum.
  • Linum catharticum and Linum perenne ssp. anglicum (as L. perenne): Eng. Bot 289–290, 1864.
  • Linum mexicanum: Bot. Reg. 1326, 1830. 
  • Linum usitatissimum: Eng. Bot 292, 1864. 
  • Radiola linoides (as Radiola millegrana): Eng. Bot 288, 1864.
  • Linum and Radiola (B. Ent. compilation).
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