Empetraceae S.F. Gray
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. Leaves without a persistent basal meristem.
Leaf anatomy. Mucilaginous epidermis present. Stomata present; anomocytic.
Lamina dorsiventral. Minor leaf veins without phloem transfer cells (Empetrum).
Stem anatomy. Young stems cylindrical. Cork cambium present; initially deep-seated. Nodes unilacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with tracheids; with vessels. Vessel end-walls scalariform, or scalariform and simple. Wood parenchyma paratracheal (scanty).
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 unit 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 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 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, biochemistry. Cyanogenic (doubtfully), or not cyanogenic (mostly). Alkaloids absent (one species). Iridoids not detected. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin (plus gossypetin). Ellagic acid present (a trace, in Empetrum). Arbutin absent. 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.
• Technical details: Empetrum nigrum.
• Empetrum nigrum var. rubrum: as E. rubrum, Bot. Reg. 1783, 1836.
• Empetrum nigrum (B. Ent.).