Trees (up to c. 12 m tall), shrubs or perennial to annual herbs, glabrous or with simple uniseriate hairs, with glandular canals or lacunae containing resins (amber), essential oils (pellucid or 'pale') and often hypericin and pseudo-hypericin (red to blackish or 'dark'). Stems green to yellow-brown or red and with 2-4(-6) raised lines along each internode when young, those lines decurrent from the midrib of the leaf above usually most prominent (sometimes expanded to form narrow wings), eventually usually terete, or wholly terete in some herbs; glabrous or with indumentum; eglandular or with pale to dark glands (sometimes ± prominent) or glandiferous, simple or rarely branched emergences; bark smooth, red-brown to purple-brown or silvery, thin or rarely corky, exfoliating in sheets, patches or irregular strips, not exuding resiniferous sap or latex. Leaves opposite, decussate or sometimes in alternating whorls of 3-4, exstipulate, sessile to shortly and gradually petiolate, sometimes with basal articulation, free or ± united, deciduous at or above the articulation or persistent; lamina entire or occasionally with gland-fringed auricles or base, rarely wholly glandular-denticulate or -fimbriate, venation parallel-dichotomous to pinnate or 1-nerved, open or closed, the tertiary absent to densely reticulate; glands linear to punctiform, pale and/or dark, marginal to laminar; indumentum absent or present. Inflorescence terminal, cymose, 1-∞-flowered, elaborated acrotonally by dichasium/monochasium-formation or pseudo-dichotomy or a mixture of both methods ('inflorescence mixed'), basitonally by axillary flowers or flowering branches, sometimes becoming thyrsoid or occasionally racemose by suppression of the terminal bud; transition from leaves to sepals sudden or gradual; bracts and bracteoles often present, usually more similar to sepals, persistent as long as leaves or occasionally (sects. 3, 4) caducous. Flowers bisexual, actinomorphic, stellate to campanulate or rarely pseudo-tubular, homostylous or rarely dimorphically heterostylous.Sepals 4-5 (or abnormally 6 or 3), quincuncial or opposite and decussate (rarely almost open in sect. 20), equal or ± unequal, sometimes foliaceous, free or up to 0.7 united, persistent or occasionally deciduous, with margin entire or glandular-denticulate to -fimbriate or eglandular-fimbriate; veins 1-c. 11, parallel or divergent, dichotomising or pinnately branched; glands marginal to laminar, linear to punctiform, pale and/or dark; indumentum absent or on dorsal surface only. Petals lemon to golden yellow or orange or rarely cream or white, often tinged or veined red dorsally where visible in bud or very rarely wholly carmine-red, 4—5 (or abnormally 6 or 3), contorted, equal, free, persistent or deciduous, asymmetrical (except in reduced forms), entire or with sessile marginal glands or glandular-ciliate, usually with ± evident projection at apical point of margin in bud ('apiculus'), rarely with entire and cucullate or trifid and flat ligule; veins numerous to few, sometimesdichotomising or forming loops, reaching margin or not; glands laminar and often marginal, punctiform to linear, pale and/or dark; indumentum absent. Stamen fascicles 4-5, antipetalous, free or variously united (2+1 + 1 + 1,2 + 2+ 1, (5), (4)) and then with double fascicles antisepalous, glabrous, persistent or deciduous, each with 1-c. 60 stamens; filaments yellow to orange or rarely cream or white or crimson, slender, united towards the base only or apparently free or united to above the middle in a few '3'-fascicled species; anthers yellow to orange or reddish, oblong to elliptic, almost isodiametric, bithecal, with amber to red or blackish gland on connective, dorsifixed (or rarely apparently basifixed, sect. 4), dehiscing introrsely by longitudinal slits; pollen tricolporate, spheroidal to prolate, with exinemicroreticulate to reticulate or a tectum perforatum. Staminode fascicles absent or rarely 3, alternating with 1 + 2 + 2 stamen fascicles, scale-like, entire or bilobed, functioning like grass lodicules. Ovary 2-5-merous, glabrous, with placentation incompletely to completely axile or ± parietal; styles 2-5, elongate, free or partially or completely united, with stigmas distinct, minute to capitate; ovules 2-∞ on each placenta, erect to horizontal or pendulous. Fruit capsular, 2-5-valved, dehiscing septicidally from the apex, with valves somewhat woody or coriaceous to papyraceous, persistent or rarely deciduous, rarely tardily dehiscent or indehiscent with valves ± fleshy and coloured red to blackish, valves l-∞-seeded; vittae often ± prominent, linear or punctiform ('vesicles'), amber or rarely blackish; styles wholly or partially persistent. Seeds small (0-3-2 mm long), narrowly cylindric to ovoid-cylindric or ellipsoid, slightly curved or usually straight, without or with a prominent unilateral carina or thin and papyraceous wing, without or with an apical and sometimes also a basal expansion, wing-like or thick, or rarely an apical whitish caruncle (sect. 25); testa yellow-brown to red-brown orpurple-brown ('blackish') with sculpturing ± prominently reticulate or linear-reticulate to foveolate or scalariform or papillose; endosperm absent; embryo slender, straight, with cotyledons equal, free, plano-convex, shorter than hypocotyl.
BASIC CHROMOSOME NUMBERS(x): 12, 11, 10, 9, 8, 7, 6;ploidy2-6.
Dry, semi-desert areas (e.g. southern Turkey and adjacent Syria and Iraq) to shallow water, in cold temperate to warm temperate climates.
World-wide except for (1) southern Chile, Argentina and the Antarctic regions, (2) southern Oceanic islands, (3) tropical lowlands (exceptH. japonicum, which occurs there as a rice-field weed), (4) Arctic, subarctic, and alpine regions. Apparently absent from thefollowing territories: Alaska, Falkland Is., Antarctica, Greenland, Iceland, Svalbard, LesserAntilles, Trinidad, Tobago, Dutch W. Indies, Surinam, Cayenne, Cape Verde Is., S. AtlanticIs., W. Sahara-Mali-Niger-Dahomey westward (except Guinea), Central African Republic,Gabon, Congo-Brazzaville, S. Tomé, Principe, Annobon, Equatorial Guinea (mainland),Aldabra, Seychelles, Mauritius, Rodriguez, Indian Ocean islands, Kuwait, Arab Emirates,Oman, Bahrain, Qatar, S. Yemen (mainland), Mongolia, Pacific Ocean islands (except NewCaledonia, Hawaii, Galapagos, and Revilla Gigedos Islands).