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The families of flowering plants

L. Watson and M.J. Dallwitz

Hydrophyllaceae R. Br. ex Edwards

~ Boraginaceae.

Including Hydroleae (Hydroleaceae) R.Br.

Habit and leaf form. Herbs (usually), or shrubs (sometimes spiny). Annual, biennial, and perennial; with a basal aggregation of leaves, or without conspicuous aggregations of leaves. Mesophytic. Leaves alternate, or opposite; spiral; petiolate; non-sheathing; not gland-dotted; without marked odour, or foetid; simple, or compound; when compound, pinnate, or palmate (rarely); when pinnate, imparipinnate. Lamina dissected, or entire; when simple/dissected, pinnatifid; pinnately veined, or palmately veined (rarely); cross-venulate. Leaves exstipulate; leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral (usually), or bifacial (occasionally dorsiventral). Stomata present; mainly confined to one surface (abaxial), or on both surfaces; anomocytic. Hairs present; eglandular and glandular (stalked glandular hairs with heads of different forms recorded in most genera); unicellular, or multicellular (commonly conical, unicellular and thick-walled, these occasionally becoming bicellular, sometimes unicellular-arachnoid and forming a dense felt, often encrusted with calcium carbonate, sometimes seated on multicellular pedicels). Cystoliths present (sometimes, associated with hairs), or absent. The mesophyll containing crystals (but infrequent). The crystals druses. Minor leaf veins with phloem transfer cells (5 genera), or without phloem transfer cells (Wigandia).

Axial (stem, wood) anatomy. Cork cambium present; initially superficial. Nodes unilacunar. Primary vascular tissues variously in a cylinder, without separate bundles, or comprising a ring of bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening absent (sometimes?), or developing from a conventional cambial ring.

The wood semi-ring porous, or diffuse porous. The vessel end-walls simple. The vessels without spiral thickening. The axial xylem with tracheids, or without tracheids; without vasicentric tracheids; with fibre tracheids; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal (diffuse).

Reproductive type, pollination. Plants hermaphrodite. Pollination entomophilous; via hymenoptera.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (usually), or solitary (rarely); when aggregated, in cymes. The ultimate inflorescence units cymose. Inflorescences ‘boraginoid’ cincinni. Flowers often ebracteolate; regular; usually 5 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk absent (usually), or present.

Perianth with distinct calyx and corolla; (8–)10(–20); 2 whorled; isomerous. Calyx (4–)5(–10); 1 whorled; gamosepalous, or polysepalous (sometimes ‘lobes divided to the base’); regular; imbricate. Epicalyx present (as appendages between the calyx lobes), or absent. Corolla (4–)5(–10); 1 whorled; appendiculate (often having scales of dubious morphological interpretation inside the tube, alternating with the stamens), or not appendiculate; gamopetalous; imbricate, or contorted; rotate, or campanulate, or funnel-shaped; regular; blue, or purple, or white.

Androecium (4–)5(–10) (as many as C). Androecial members adnate (to the corolla tube, and usually with basal appendages also united to the corolla, which in Hydrophyllum form tubes leading to the nectar); all equal, or markedly unequal; free of one another; 1 whorled. Androecium (at least ostensibly) exclusively of fertile stamens (but see remarks below re interpretation of corolla ‘scales’). Stamens (4–)5(–10); inserted near the base of the corolla tube; isomerous with the perianth; oppositisepalous (alternating with the petals); alternating with the corolla members. Filaments variously, basally appendiculate. Anthers dorsifixed; versatile; dehiscing via longitudinal slits; introrse; appendaged. Microsporogenesis simultaneous. Tapetum glandular. Pollen grains aperturate; 3 aperturate, or 5–6 aperturate; colpate, or colporate, or rugate; 2-celled (in 3 genera).

Gynoecium 2 carpelled. The pistil 1 celled, or 2 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior (usually), or partly inferior (sometimes). Ovary 1 locular, or 2 locular. Gynoecium median; stylate. Styles 1, or 2; free, or partially joined; attenuate from the ovary; apical. Stigmas dry type; papillate; Group II type. Placentation when unilocular, parietal; when bilocular, axile. Ovules in the single cavity when unilocular, 2–100 (i.e. to ‘many’); when bilocular 2–50 per locule (i.e. to ‘many’); funicled, or sessile; pendulous (when funicled); epitropous (the micropyle directed upwards and outwards); non-arillate; anatropous, or amphitropous; unitegmic; tenuinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed, or not formed (then the three nuclei degenerating early — Hydrolea); when formed, 3; not proliferating; ephemeral. Synergids sometimes with filiform apparatus. Endosperm formation cellular, or nuclear, or cellular to nuclear. Embryogeny solanad.

Fruit non-fleshy; dehiscent (usually), or indehiscent; a capsule, or capsular-indehiscent. Capsules when dehiscent, loculicidal (usually), or splitting irregularly, or septicidal (rarely). Seeds copiously endospermic. Endosperm oily. Cotyledons 2. Embryo chlorophyllous (1/1), or achlorophyllous (1/2); straight (spathulate or linear).

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Ellisia. Not cyanogenic. Alkaloids absent (6 species). Iridoids not detected. Saponins/sapogenins present (rarely), or absent. Proanthocyanidins absent. Flavonols present; kaempferol and quercetin. Ellagic acid absent (2 genera). Aluminium accumulation not found.

Geography, cytology. Temperate to tropical. Widespread. X = 5–13(+).

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Solaniflorae; Boraginales. Cronquist’s Subclass Asteridae; Solanales. APG III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order Solanales (as a synonym of Boraginaceae).

Species 250. Genera 18; Codon, Conanthus, Draperia, Ellisia, Emmenanthe, Eriodictyon, Eucrypta, Hesperochiron, Hydrolea, Hydrophyllum, Nama, Nemophila, Phacelia, Pholistoma, Romanzoffia, Tricardia, Turricula, Wigandia.

General remarks. Differing from Boraginaceae in the ebracteolate flowers, ovary with attenuate style and pendulous ovules, and the capsular fruits; also in the record of solanad embryology. Regarding corolla scales exhibited here, Lindley (1835) remarked: “We would take the present opportunity of suggesting that the 10 scales (exemplified in in Phacelia tanacetifolia) represent 5 sterile anthers adhering to the tube of the corolla by their backs, and consisting each of two membranous lobes. This is chiefly rendered probable by their number and position; but we are not aquainted with any direct evidence of such being the true nature of these singular appendages.” This exemplifying Lindley's pre-Darwinian approach to comparative morphology, and giving the lie to the widely held notion that the later obsession with phylogenetic speculation led to a revolution in taxonomic descriptive technique. Numerous, parallel zoological examples can be seen in John Curtis's ‘British Entomology’ (1824–1840).

Illustrations. • Le Maout and Decaisne: Hydrophyllum virginicum, Phacelia, Ellisia. • Le Maout and Decaisne: Hydrolea azurea, Wigandia caracasana. • Conanthus aretioides, as Eutoca: Hook. Ic. Pl. 4 (1841). • Hydrolea spinosa: Bot. Reg. 566, 1821. • Nemophila menziesii var. atomaria: as N. atomaria, Bot. Reg. 1940, 1837. • Nemophila phacelioides: Bot. Reg. 740, 1823. • Phacelia campanularia: Bot. Mag. 110 (1884). • Phacelia divaricata: as Eutoca, Bot. Reg. 1784, 1836. • Phacelia tanacetifolia: Bot. Reg. 1696, 1835. • Phacelia viscida: as Eutoca, Bot. Reg. 1808, 1836. • Wigandia caracasana: Bot. Reg. 1966, 1837.

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: 15th April 2018.’.