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The families of flowering plants

L. Watson and M.J. Dallwitz

Empetraceae S.F. Gray

~ Ericaceae.

Habit and leaf form. Small shrubs. Xerophytic. Leaves evergreen; small; more or less whorled, or alternate; spiral; rolled (ericoid); leathery; shortly petiolate; non-sheathing; simple; pulvinate. Lamina entire; acicular, or linear; one-veined, or pinnately veined (?). Leaves exstipulate. Lamina margins revolute. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral. Mucilaginous epidermis present. Stomata present; mainly confined to one surface (abaxial); anomocytic. Hairs present (confined to the entrance to central leaf cavity, see illustration); eglandular and glandular (the former unicellular, simple-elongate and forming a tangled mass confined to and obstructing the leaf cavity; the latter comprising uni- or pluricellular, ellipsoidal heads on short, unicellular or unisetiate stalks). Complex hairs absent. The mesophyll containing crystals, or without crystals (absent or rare in E. nigrum). The crystals when seen, druses. Minor leaf veins without phloem transfer cells (Empetrum).

Axial (stem, wood) anatomy. Young stems cylindrical. Cork cambium present; initially deep-seated. Nodes unilacunar. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow.

The wood ring porous to semi-ring porous. The vessels extremely small; almost exclusively solitary. The vessel end-walls scalariform (in Empetrum, with up to 10 bars), or scalariform and simple (in Ceratiola and Corema). The vessels without vestured pits; without spiral thickening. The axial xylem with tracheids; with fibre tracheids to without fibre tracheids; with libriform fibres to without libriform fibres (the fibres with numerous small bordered pits); without septate fibres. The fibres without spiral thickening. The parenchyma very scanty paratracheal. ‘Included’ phloem absent. The wood not storied.

Reproductive type, pollination. Plants dioecious (usually), or monoecious (sometimes), or polygamomonoecious (occasionally with a few perfect flowers, very rarely all or most perfect). Gynoecium of male flowers vestigial, or absent.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’. The ultimate inflorescence units when aggregated, racemose. Inflorescences terminal, or axillary; few-flowered terminal heads, or 1–3 flowered in leaf axils. Flowers (one to several) bracteolate; small (and inconspicuous); regular; 3 merous; cyclic; when hermaphrodite, tricyclic to tetracyclic. Free hypanthium absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla, or petaline, or sepaline (but then mostly somewhat petaloid); 3–4 (Corema), or (5–)6; 1 whorled (Corema), or 2 whorled; isomerous; similar in the two whorls to different in the two whorls. Calyx (2–)3; 1 whorled; polysepalous; regular; imbricate. Corolla when present, (2–)3; 1 whorled; polypetalous; imbricate; regular. Petals shortly clawed to sessile.

Androecium 2 (Ceratiola), or 3(–4). Androecial sequence not determinable. Androecial members free of the perianth; free of one another; 1 whorled. Androecium of male flowers, exclusively of fertile stamens. Stamens 2 (Ceratiola), or 3(–4); reduced in number relative to the adjacent perianth, or isomerous with the perianth; oppositisepalous; alternating with the corolla members (alternating with the petals, when these are distinguishable). Anthers becoming inverted during development, their morphological bases ostensibly apical in the mature stamens; dehiscing via longitudinal slits; extrorse, or latrorse; bilocular; tetrasporangiate; unappendaged. Endothecium not developing fibrous thickenings. Pollen shed in aggregates; in tetrads. Pollen grains aperturate; 3 aperturate; colporate; 2-celled.

Gynoecium 2–9 carpelled. Carpels reduced in number relative to the perianth to increased in number relative to the perianth. The pistil 2–9 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary 2–9 locular; sessile. Gynoecium shortly stylate. Styles 1 (variously cleft); from a depression at the top of the ovary; apical. Stylar canal present. Stigmas 1 (then lobed), or 2–9. Placentation basal to axile. Ovules 1 per locule; funicled; ascending; apotropous; with ventral raphe; non-arillate (non-carunculate); anatropous to campylotropous; unitegmic; tenuinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids pear-shaped. Endosperm formation cellular. Endosperm haustoria present; chalazal and micropylar. Embryogeny solanad.

Fruit fleshy to non-fleshy; indehiscent; a drupe. The drupes with separable pyrenes (2–9). Fruit 2–9 seeded. Seeds endospermic. Endosperm oily. Embryo well differentiated. Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. Cyanogenic (doubtfully), or not cyanogenic (mostly). Alkaloids absent (one species). Arbutin absent. Iridoids not detected. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin (plus gossypetin). Ellagic acid present (a trace, in Empetrum). Ursolic acid present. Aluminium accumulation not found.

Geography, cytology. Holarctic, Neotropical, and Antarctic. Frigid zone and temperate. North temperate, Andes, Falklands. X = 13.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Ericales. Cronquist’s Subclass Dilleniidae; Ericales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; Order Ericales (as a synonym of Ericaceae).

Species 10–20. Genera 3; Ceratiola, Corema, Empetrum.

General remarks. See comments under our sensu stricto description of Ericaceae, from which this small family differs in numerous characters.

Illustrations. • Corema conradii, as Oakesia: Hook. Ic. Pl. 5–6 (1842–3). • Technical details: Empetrum nigrum. • Empetrum nigrum var. rubrum: as E. rubrum, Bot. Reg. 1783, 1836. • Empetrum nigrum (B. Ent., 1834). • Empetrum nigrum: transverse section of leaf (Solereder, 1908).

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: 13th March 2017.’.