| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Linaceae S.F. Gray

Excluding Ctenolophacaceae, Erythroxylaceae, Hugoniaceae, Lepidobotryaceae.

Habit and leaf form. Herbs and shrubs (mostly), or trees (a few, small), or lianas (a few). ‘Normal’ plants. Self supporting (mostly), or climbing; the climbers tendril climbers (with tendrils like coiled watch springs arising from the secondary branches). Mesophytic, or xerophytic. Leaves alternate to opposite; usually spiral; subsessile to sessile; non-sheathing; simple. Lamina entire. Leaves stipulate, or exstipulate. Stipules small, sometimes represented by glands; caducous. Lamina margins entire. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral. Mucilaginous epidermis present, or absent. Stomata present; mainly confined to one surface, or on both surfaces; commonly paracytic. Hairs present (usually narrow, unicellular or rarely multicellular, of varying length, but a glandular-shaggy form found in Linum). The mesophyll with sclerenchymatous idioblasts, or without sclerenchymatous idioblasts. Minor leaf veins with phloem transfer cells (Linum), or without phloem transfer cells (Linum, Radiola).

Axial (stem, wood) anatomy. Young stems with solid internodes, or with spongy internodes. The cortex containing cristarque cells, or without cristarque cells. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles (then the bundles distinct but close together); collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow.

The wood diffuse porous. The vessels medium; usually exclusively solitary. The vessel end-walls exclusively or predominantly simple. The vessels without vestured pits; without spiral thickening. The axial xylem with tracheids; commonly with vasicentric tracheids; with fibre tracheids; without libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal, or paratracheal, or apotracheal and paratracheal (often difficult to classify); wood not storied. Tyloses usually absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence units 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). 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. Ovary 1 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, phytochemistry. C3. C3 physiology recorded directly in Linum. Anatomy non-C4 type (Linum). Sugars transported as sucrose, or as oligosaccharides + sucrose, or as sugar alcohols + oligosaccharides + sucrose (?). Cyanogenic, or not cyanogenic. Cynogenic constituents of Hegnauer’s ‘Group C’. Alkaloids absent (4 species). Iridoids not detected. Saponins/sapogenins absent. Proanthocyanidins absent. Flavonols absent. Ellagic acid absent (2 genera, 3 species). Aluminium accumulation not found.

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 III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Malpighiales.

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

Illustrations. • Le Maout and Decaisne: Linum. • Linum and Radiola (B. Ent. compilation). • Anisadenia pubescens: Hook. Ic. Pl. 26 (1899). • Linum catharticum and Linum perenne ssp. anglicum (as L. perenne): Eng. Bot 289–290, 1864. • Linum grandiflorum: Bot. Mag. 82 (1856). • Linum macraei: Bot. Mag 90 (1864). • Linum mexicanum: Bot. Reg. 1326, 1830. • Linum monogynum: Bot. Mag. 64 (1837). • Linum usitatissimum: Eng. Bot 292, 1864. • Linum usitatissimum: Köhler’s Medizinal Pflanzen 1 (1887). • Radiola linoides (as Radiola millegrana): Eng. Bot 288, 1864. • Reinwardtia tetragyna: Bot. Mag. 116 (1890). • Tirpitzias sinensis (as Reinwardtia): Hook. Ic. Pl. 26 (1899).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

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