Hypericum tetrapterum (Nomenclature)
Perennial herb (0.15-)0.2-0.7(-1.2) m tall, erect to ± decumbent or rarely ascending to procumbent from creeping and rooting base, with stems numerous to few, initially unbranched below inflorescence, later branched above for half to most of their length. Stems ± broadly 4-winged, the subsidiary wings narrower or rarely with wings equally narrow, with black glands on the lines and sometimes elsewhere; internodes 7-50 mm, shorter than to exceeding leaves. Leaves sessile or rarely (especially the lower) up to 0.5 mm petiolate; lamina (6-) 9-40 ´ (4-)7-24 mm, ovate or elliptic or triangular-ovate to orbicular, somewhat paler beneath, thinly chartaceous; apex rounded to very rarely apiculate-obtuse, margin plane or rarely ± undulate, base rounded to cordate-amplexicaul; venation: 1-3 pairs of main laterals from base of midrib; tertiary reticulation dense, rather obscure; laminar glands pale, dense, small; intramarginal glands black, rather close, uniform. Inflorescence (1-)10-35(-c. 70)-flowered, from 1-2(-4) nodes, with flowering branches ascending from up to 10 nodes, the whole cylindric to corymbiform, dense or with partial inflorescences dense; pedicels 1-2 mm; bracts and bracteoles 2-3mm long, lanceolate to linear, entire, with 0-4 black glands. Flowers 10-15 mm in diam., stellate; buds ellipsoid, subacute. Sepals 5, equal, 3-5 ´ 1-1.5 mm, lanceolate to narrowly oblong, acute to acuminate, entire, erect in bud and fruit; veins 3 with outer pair branched or 5 unbranched; laminar glands striiform to punctiform or occasionally basal linear, all pale or 1-2 black; marginal glands absent or rarely up to 7, black, immersed. Petals 5, rather pale yellow, not tinged red, 5-8 ´ 2-3(-4) mm, c. 1.4 ´ sepals, oblanceolate, entire or distally unilaterally crenate; laminar glands absent or rarely few, punctiform, black and pale [ch]; marginal glands 1-4 or usually absent. Stamens 30-40(-60), '3'-fascicled, longest c. 4.5-7.5 mm, c. 0.9 ´ petals. Ovary 3-locular, 2-2.5 ´ 1-1.5 mm, narrowly ovoid; styles 3, free, 2-3.5 mm, 0.8-1.4 ´ ovary, widely spreading. Capsule 5-7(-8) ´ 2.4-4 mm, c. 2 ´ sepals, narrowly cylindrical-ellipsoid to ovoid; valves with longitudinal linear vittae. Seeds dark brown, 0.6-0.8(-1.1) mm, cylindric, not carinate or appendiculate; testa finely foveolate.
2n = 16 (Stenar, 1938; Noack, 1939; Pólya, 1950; Robson, 1956; Gadella & Kliphuis, 1966; Zhukova, 1967), n = 8 (Nielsen, 1924; Winge, 1925; Chattaway, 1926; Noack, 1939; Sugiura, 1944).
In wet habitats - marshes, streamsides, open ditches, wet meadows, springs; 0-1300 m (Switzerland, Valais), -1900 m (Corsica), -2000 m (Turkey).
Europe from Scotland (Orkney and Sutherland southward), Denmark, S. Sweden (Skåne), Poland, the SW. Ukraine and Transcaucasia south to Spain, Algeria, Sicily, Greece, Turkey, N. Israel, N. Iraq and NW. Iran.
The variation in H. tetrapterum is wide but almost continuous, from a tall, branching, relatively narrow-leaved form in southern Italy and Sicily ( 'H. neapolitanum') to short unbranched forms in northern Europe. In two areas, however, decumbent small-leaved few-flowered high-altitude forms have developed - Corsica and Turkey (Amanus). Although in neither area have field studies been made to decide how distinct these forms are from the adjacent typical form, they both seem worth recognising at least until such studies are made.
H. tetrapterum is related to 2b. H. undulatum var. undulatum, differing from it in the more broadly winged stem internodes, the usually relatively broader leaves with plane margin, and the denser inflorescence with smaller flowers, sepals with fewer black laminar glands, and paler petals that are not tinged rednot tinged red. The form most similar to var. undulatum occurs in southern Italy and Sicily ("H. neopolitanum Ten.").
Wahlenberg (Fl. suec.: 476 (1826)) makes H. alatum Retz a synonym of his H. quadrialatum along with "H. quadrangulare Sm." and H. tetrapterum Fr.; but the original description (e.g. ...caule...subtomentoso, calycibus serrulato-glandulosis) clearly applies to quite another plant.