Perennial herb 0.2-0.6(-1) m tall, erect or rarely decumbent to procumbent from creeping and rooting base, budding on roots late in season, with stems numerous to few, much branched especially distally. Stems 2-lined, with few black glands on lines; internodes 5-25 mm, shorter than leaves. Leaves sessile to 1 mm petiolate; lamina (5-)10-25(-30) ´ 3-10 mm, oblong or elliptic to linear or rarely orbicular, paler beneath, chartaceous; apex obtuse or apiculate to rarely acute, margin plane or ± recurved to revolute, base subcordate (or rarely cordate)-amplexicaul to rather narrowly cuneate; venation: c. 2 pairs of main laterals from lower quarter to eighth of midrib, tertiary reticulation lax or scarcely visible; laminar glands pale, scattered and sometimes black, few, punctiform; intramarginal glands black, spaced, interspersed with small dense pale ones. Inflorescence 3- to numerous-flowered, from 1-3 nodes, with flowering branches curved-ascending from up to 15 or sometimes more nodes below, the whole cylindric to broadly pyramidal or subcorymbiform; pedicels c. 0.5-2 mm; bracts and bracteoles up to 4(-7) mm long, narrowly lanceolate to linear, entire. Flowers 15-25(-35) mm in diam., stellate; buds narrowly ovoid, acute. Sepals 5, equal, 3-7 ´ 0.7-1.5 mm, narrowly oblong or lanceolate to linear, acute to finely acuminate with acumen sometimes glandular, entire, erect in bud, recurved in fruit; veins 3(5), unbranched; laminar glands pale and often a few black, in 2(4) rows, striiform (basally) to punctiform; intramarginal glands few, black or absent. Petals 5, golden yellow, not tinged red in bud, (8-)12-15 ´ 5-6 mm, 3-4 ´ sepals, oblong to oblong-elliptic, asymmetric, distally ± crenate; laminar glands all pale to mostly black, linear or partly striiform to punctiform; intramarginal glands black, distal, in sinuses when present. Stamens 40-60, '3'-fascicled, longest 6-8 mm, c. 0.5-0.7 ´ petals; anther gland black. Ovary 3-locular, 3-5 ´ 1.3-1.8 mm, narrowly ovoid to ovoid-ellipsoid; styles 3, free, 4-6 mm, c. 1.5-2 ´ ovary, broadly to rather narrowly spreading; stigmas narrow. Capsule 3-10 ´ 3-6 mm, 0.7-1.5 ´ sepals, narrowly to broadly ovoid or narrowly ovoid-conic; valves with dorsal vittae and lateral vittae or yellowish, striiform to punctiform vesicles. Seeds dark brown, c. 1mm, cylindric, not carinate or appendiculate; testa finely linear-foveolate.
See Salisbury (1`942: 106), Hagemann (1983: 106, f. 3 and refs.).
2n = 32 (Noack, 1939, Mulligan, 1957 et auct. plur.; n = 16, Nielsen, 1924, Hoar & Haertl, 1932, Noack, 1939 et auct. plur.), 48 (Noack, 1939, Robson, 1981, Ciccarelli, Garbari & Mártonfi, 2001), 2n = 16 (Schwarz, 1965, as H. veronense; Strid & Franzén, 1981, as var. angustifolium; Papanicolaou, 1984, Ciccarelli, Garbari & Mártonfi, 2001, as H. perforatum).
Open woodland, meadows, grassland and steppes, riverbanks, stony and grassy slopes, roadsides, in dry or well-drained habitats; 10-c. 2750 m (China), -2300 m (USSR), -3150 m (Afghanistan).
General distribution of the species:- Europe (except extreme north), north-west Africa, Canary Is., Madeira, Azores; Turkey, Cyprus, the Levant and western Saudi Arabia to north-west India (Uttar Pradesh), Transcaucasia, Turkmenistan to Altai, Angara-Sayan and NW. Mongolia; China (W. Xinjiang and from Gansu east to Hebei, south to Jiangxi and west to Yunnan). Introduced into many other parts of the world, viz. Canada, U.S.A., Mexico, Cuba, Haiti, Brazil (Paraná), Uruguay, Argentina, Chile, Juan Fernandez, Sudan Rep. (Jebel Marra), S. Africa, Réunion, Australia, New Zealand, Japan.
Hypericum perforatum is apparently an allotetraploid (2n=32) (Gustafsson, 1947; Robson, 1958, 1975), which, for reasons of morphology and geography, would appear to have arisen from a cross between two diploid taxa (2n=16), viz. 1a. H. maculatum subsp. immaculatum (Balkans) and 6. H. attenuatum (western Siberia to China). Morphologically it (or, rather, typical broad-leaved var. perforatum) is close to H. maculatum, but it differs in the 2-lined stem internodes, the more oblong leaves with lax reticulate venation and rather dense pale laminar gland dots, the lanceolate acute sepals, and the petals with black marginal glands, characters that all tend towards H. attenuatum. It differs from both presumed parents in its capsule valves with oblique vittae or vesicles, a glandular pattern that is unique in sect. Hypericum (of which it is the type species). The presence of linear laminar glands in the petals and pale laminar leaf glands suggests that the maculatum parent was var. immaculatum rather than var. maculatum, with its punctiform to striiform petal glands and usual lack of pale laminar leaf glands. If, as seems probable, the ancient hybridisation occurred in Central Asia (the Altai region?), then (i) the current restricted distribution of var. immaculatum in the Balkans is a relict of a much wider one, and (ii) the extension of the current distribution of var. maculatum into Central Asia is relatively recent.
Cytologically, H. perforatum behaves as a hybrid (Noack, 1939; Gustafsson, 1946-47; Mártonfi et al., 1996a). The pollen undergoes normal reduction division; but meiotic abnormalities (lagging chromosomes) lead to sterility that is usually about 30% but can be up to 70% (Nielsen, 1924; Hoar & Haertl, 1932). Only c. 3% of the embryo sacs are produced by normal meiosis (n=16), the remaining (unreduced) ones being produced parthenogenetically (n=32). The latter, however, are pseudogamous, i.e. they require pollination for seed development. Fertilisation is therefore possible, though not necessary. Occasionally the n=32 embryo sacs are fertilised, resulting in hexaploid (2n=48) plants. The records of H. perforatum with 2n=16 chromosomes (see p. ) would appear to be from dihaploids, i.e. from plants that have resulted from the development of reduced but unfertilised embryo sacs. Since in allotetraploids (i) each chromosome is duplicated and (ii) the more different the parents are, the less is the likelihood that there will be multiple chromosome associations, it seems reasonable to expect dihaploids to occur in H. perforatum. Two of these occurrences have been reported in the more reduced forms of the species (var. angustifolium and var. microphyllum), and two (Papanicolaou, 1984; Ciccarelli, Garbari & Mártonfi, 2001) were in H. perforatum without qualification. Gagnieu & Wilhelm's report (1965) of n=12 for var. angustifolium is no doubt either a miscount for n=16 or, just possibly, from fertilisation by a triploid pollen grain. This cytological variation is accompanied by wide morphological variation, which is complicated in the wild by 'back-crosses' to at least two of the subspecies of H. maculatum (Robson, 1981: 168, f. 55) (see p. ).
The morphological variation in H. perforatum, though great, appears to be continuous and therefore theoretically indivisible. For reasons of practicality, however, it is convenient to recognise some previously described variants as subspecies, a rank that reflects their geographical basis better than the hitherto more usual varieties. For one well-known taxon, however, even this is impossible. The southern European plants with narrow leaves and vesicular capsule vittae ('var. angustifolium DC.') cannot be separated from those with small (narrow to broad) leaves and similar capsule vittae ('var. microphyllum DC.'). Indeed, the latter are probably polyphyletically derived from the former, and some may be merely the result of habitat-induced variation. Bearing in mind these reservations, the overall variation in H. perforatum can be described and classified in four intergrading subspecies.
(a) From its presumed origin in western Siberia into northern and central Europe and eastward into NW. Mongolia the initially sessile leaves become gradually shortly petiolate (although remaining sessile in northern Russia (always?) and sometimes in Scandinavia), and the base changes from rounded to broadly cuneate, the capsule vittae remaining continuous and almost always narrow. This is the type form (subsp. a. perforatum). In dry habitats the leaves become narrow with revolute margins, thus superficially resembling a form of subsp. veronense (see c. below); but the leaves are petiolate and the capsule glands are different. Such plants have frequently been recorded as 'var. angustifolium DC.', but the vesiculate capsule vittae differ from those of similar forms of subsp. veronense. Where the capsule is vesiculate (as it is, for example, in southern England on chalk, sand, wall-tops, etc.), such capsules are derived from continuous lateral vittae, as is shown by the occurrence of intermediate states. True 'var. angustifolium' would appear to have been derived from forms in which the lateral vittae have been interrupted before becoming enlarged and vesiculate. Another development of vesiculate capsules of this type in subsp. perforatum has occurred in the southern Balkans. In the mountains of Bulgaria and northern Greece there are erect to procumbent plants with small, obovate to orbicular leaves and capsules with lines of flattish vesicles ('var. humile Stranski'). These are interpreted here as an extreme montane development of subsp. perforatum, there being continuous variation from (i) typical subsp. perforatum to (ii) a smaller-leaved form with rather dense inflorescences and small fruits, then to (iii) a similar, decumbent form with capsule valves having two lines of flattish 'vesicles', and finally to (iv) a dwarf form with small narrower leaves.
(b) Both presumed parents have sessile leaves, with the base rounded in H. maculatum and subcordate to cuneate in H. attenuatum. Therefore the one variant of H. perforatum with sessile cordate-amplexicaul leaves would also appear to have a good claim to at least approach the primitive form. This is subsp. b. songaricum (var. songaricum (Ledeb. ex Rchb.) K. Koch), of which the tallest plants with the largest leaves and most luxuriant growth (approaching those of the presumed parental species) occur in eastern Kazakhstan and probably also in NW. Xinjiang. The leaves become gradually smaller southward (Kirghizstan - 'H. komarovii') and westward (W. Kazakhstan, S. Russia and the southern Ukraine - var. 'gracile ') and in dry regions develop a glaucous lower surface and recurved margins.
(c) From the Caucasus region into eastern Turkey and northern Iran narrower-leaved plants become frequent ('var. collinum' Woron.), and the capsules, which are still relatively large, have interrupted and often somewhat swollen oblique vittae. The leaves then become first narrower and then smaller (often with revolute margins) eastward into central Asia (Tadjikistan) and India (east along the Himalaya to Uttar Pradesh) and westward into the Mediterranean region, where the typical narrow-leaved and small-leaved plants of subsp. veronense (= respectively var. angustifolium DC. and var. microphyllum DC.) occur and extend into Macaronesia, NW. Africa, SW. Saudi Arabia (Asir) and the Sudan Republic (Jebel Marra), although whether its occurrence in Jebel Marra is natural is doubtful (Wickens, 1976: 76, 99, map 59). It has been introduced into various other countries and continents. Where its distribution meets that of subsp. perforatum in southern and central Europe, the intermediate forms that occur are presumably hybrid in origin, unless subsp. veronense has arisen polyphyletically in southern Europe, the Caucasus region and (possibly) Central Asia. In the trends in this subspecies the leaves first become narrow (vars collinum, angustifolium) and then small (var. microphyllum = subsp. veronense); but in relatively mesophytic areas these small leaves may become broad again (e.g. var. ellipticum Freyn non Durand & Pittier in mountain Turkmenistan).
(d) In China, after a gap in distribution from NW. Mongolia to Gansu and adjacent Qinghai (where some specimens closely approach subsp. perforatum in form), there is a southward trend to Yunnan and Guizhou in which the leaves and flowers become smaller, the latter being crowded in small (terminal and lateral) inflorescences at the end of elongated branches (subsp. d. chinense). This subspecies has been introduced into Japan ('H. foliosissimum Koidz.').
For H. perforatum var. latifolium Gaudin and synonyms, see under 17xb. H. ´ desetangsii nothosubsp. carinthiacum nothoforma perforatiforme.