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The families of flowering plants

L. Watson and M.J. Dallwitz

Violaceae Batsch.

Including Alsodeiaceae J.G. Agardh, Leoniaceae DC., Retrosepalaceae Dulac

Habit and leaf form. Herbs, or shrubs, or lianas, or ‘arborescent’ (rarely). The herbs with a basal aggregation of leaves, or without conspicuous aggregations of leaves. Self supporting, or climbing. Mesophytic, or helophytic. Leaves alternate (usually), or opposite; usually spiral; petiolate, or petiolate and subsessile, or subsessile; non-sheathing; simple; epulvinate. Lamina entire (usually), or dissected; when dissected, pinnatifid; pinnately veined, or palmately veined; cross-venulate. Leaves stipulate. Stipules free of one another. Leaf development not ‘graminaceous’. Domatia occurring in the family (Rinorea); manifested as pits (mostly), or hair tufts.

Leaf anatomy. The leaf lamina dorsiventral (usually), or centric. Mucilaginous epidermis often present. Stomata present; mainly confined to one surface (adaxial), or on both surfaces; anisocytic, or paracytic. Hairs present; eglandular, or eglandular and glandular (mostly eglandular, but shaggy glandular hairs are associated with leaf teeth in Viola spp.); unicellular, or multicellular. Unicellular hairs branched. Multicellular hairs uniseriate. Adaxial hypodermis present, or absent. Minor leaf veins without phloem transfer cells (Viola).

Axial (stem, wood) anatomy. Young stems with solid internodes, or with hollow internodes (often, in the herbs). Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles; collateral. Secondary thickening developing from a conventional cambial ring.

The wood semi-ring porous (rarely), or diffuse porous. The vessels very small (usually), or small to medium; solitary (mostly), or radially paired, or in radial multiples. The vessel end-walls scalariform, or simple, or scalariform and simple. The vessels with spiral thickening, or without spiral thickening. The axial xylem with fibre tracheids, or without fibre tracheids; with libriform fibres, or without libriform fibres; usually including septate fibres. The parenchyma sparse paratracheal (or absent); wood partially storied, or not storied. Tyloses present, or absent.

Reproductive type, pollination. Plants hermaphrodite (sometimes cleistogamous). Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, axillary; when aggregated, in cymes, or in racemes, or in heads, or in panicles. The ultimate inflorescence units cymose. Inflorescences usually racemes, panicles or heads. Flowers (bi-) bracteolate; fragrant, or odourless; somewhat irregular to very irregular (usually), or regular. The floral irregularity involving the perianth, or involving the perianth and involving the androecium. Flowers 5 merous; cyclic; tetracyclic. Free hypanthium absent.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous (usually, more or less), or gamosepalous (at the base). Calyx lobes markedly longer than the tube. Calyx unequal but not bilabiate, or regular; basally appendaged (e.g. Viola), or neither appendaged nor spurred; persistent (often); imbricate, or open in bud; with the median member posterior. Corolla 5; 1 whorled; polypetalous; imbricate (usually, with descending aestivation), or contorted; unequal but not bilabiate (usually), or regular; spurred (the enlarged anterior member, often), or not spurred. Petals clawed, or sessile.

Androecium 5. Androecial members free of the perianth; free of one another, or coherent; often 1 adelphous (forming a cylinder round the ovary); 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; isomerous with the perianth; oppositisepalous; alternating with the corolla members. Anthers cohering (often), or connivent, or separate from one another; adnate; introrse; tetrasporangiate; appendaged (the two anterior members often appendaged or spurred, the connective often prolonged), or unappendaged. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate. Anther wall initially with more than one middle layer (2 to 4). Tapetum glandular. Pollen grains aperturate; 3(–5) aperturate; colporate; 2-celled (in Ionidium and Viola).

Gynoecium (2–)3(–5) carpelled. Carpels reduced in number relative to the perianth (usually), or isomerous with the perianth. The pistil 1 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary unilocular; 1 locular. The ‘odd’ carpel anterior. Gynoecium stylate, or non-stylate (Melicytus). Styles 1 (of various forms). Stigmas 1, or 3–5 (Melicytus); truncate (or appendiculate); dry type; papillate; Group III type. Placentation parietal. Ovules in the single cavity 1–100 (to ‘many’); arillate; anatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle, or not contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing only after one has been fertilized, or fusing simultaneously with the male gamete (?). Antipodal cells formed; 3; not proliferating; ephemeral (usually), or persistent (Hybanthus concolor). Synergids often hooked (but only rarely with filiform apparatus). Endosperm formation nuclear. Embryogeny asterad.

Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule, or a berry, or a nut (rarely). Capsules loculicidal and valvular. Fruit when capsular, elastically dehiscent. Seeds endospermic. Endosperm oily. Seeds winged, or wingless. Cotyledons 2; flat. Embryo chlorophyllous (8 species of Viola); straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Viola. Anatomy non-C4 type (Viola). Inulin recorded (in Ionidium). Not cyanogenic. Alkaloids present, or absent. Iridoids not detected. Saponins/sapogenins present, or absent. Proanthocyanidins absent. Flavonols present; kaempferol, or kaempferol and quercetin. Ellagic acid absent (4 genera, 4 species). Aluminium accumulation demonstrated.

Geography, cytology. Frigid zone to tropical. Cosmopolitan. X = 6–13, 17, 21, 23.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Violiflorae; Violales. Cronquist’s Subclass Dilleniidae; Violales. APG III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Malpighiales.

Species 900. Genera 21; Agatea, Allexis, Amphirrhox, Anchietea, Corynostylis, Decorsella, Fusispermum, Gloeospermum, Hybanthus, Hymenanthera, Isodendron, Leonia, Mayanaea, Melicytus, Noisettia, Orthion, Paypayrola, Rinorea, Rinoreocarpus, Schweiggeria, Viola.

Economic uses, etc. Over 120 species of Viola are grown as ornamentals.


Violet is for faithfulnesse
Which in me shall abide;
Hoping likewise that from your heart
You will not let it slide
(from a popular songbook, ‘A Handfull of Pleasant Delites’, first published in 1566)

Lay her in the earth,
And from her fair and unpolluted flesh
May violets spring
(‘Hamlet’, v., 1)

. . . violets dim,
But sweeter than the lids of Juno’s eyes
Or Cyatherea’s breath
(‘The Winter’s Tale’, iv., 3)

When daisies pied, and violets blue,
And cuckoo-buds of yellow hue,
And Lady-smocks all silver-white,
Do paint the meadows with delight
(‘Love’s Labour’s Lost’)

Illustrations. • Le Maout and Decaisne: Viola. • Rinorea gracilipes: Thonner. • Viola palustris, V. odorata, V. hirta, V. riviniana, V. rupestris (as V. arenaria), V. lactea: Eng. Bot. 170–174bis and 176, 1864. • Viola reichenbachiana, V. canina (as “flavicornus”), V. persicifolia (as stagnina): Eng. Bot. 174, 175 and 177 (1864). • Viola tricolor ssp. tricolor, V.tricolor ssp. curtisii, V. arvensis, V. lutea: Eng. Bot. 178–181, 1864. • British Viola species (B. Ent. compilation). • Leonia cymosa, as Steudelia: Martius, Nova Gen. et Spec. Pl. Brasiliensium 2 (1826). • Melicytus crassifolius (as Hymenanthera): Hooker, Fl. Novae-Zelandiae (1853). • Melicytus lanceolatus: Hooker, Fl. Novae-Zelandiae (1853). • Rhinorea castanaefolia, as Conohoria: Hook. Ic. Pl. 1 (1837). • Rinorea paniculata, as Alsodea: Martius, Nova Gen. et Spec. Pl. Brasiliensium (1824). • Schweiggeria fruticosa, as Glossarrhen floribundus: Martius, Nova Gen. et Spec. Pl. Brasiliensium (1824). • Schweiggeria pauciflora: Bot. Reg. 40, 1841. • Ionidium floribundum, cf. Hybanthus: Hook. Ic. Pl. 28 (1902).

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: 5th March 2018.’.