Hypericum perforatum L.
St John's wort
Glabrous perennial herb to 1 m tall, with slender rhizomes; stems erect, aerial, 2-lined, woody at base. Lvs sessile, 10-27 × 1-8 mm, lanceolate to oblong or ovate, with numerous pellucid and scattered intramarginal black glands; venation indistinct apart from main veins; base cuneate to subcordate; apex rounded, often mucronulate. Infl. terminal, a panicle of dense, many-flowered, corymbose cymes, more rarely cymes few-flowered; bracts similar to upper lvs. Sepals ± equal, 3-6 mm long, narrow-lanceolate to oblong, not accrescent, entire, acute to acuminate, sometimes with scattered black glands, sometimes the glands pellucid. Corolla 8-20 mm diam., golden, with scattered to numerous black marginal glands; petals obovate, much > sepals. Stamens in 3 bundles, < or = petals. Styles 3, = or > ovary. Capsule 6-8 mm long, narrow-ovoid, dry. Seeds 0.8-1.3 mm long, broad-cylindric, rugose.
N.; S.: very common.
Europe, W. Asia, N. Africa 1869
A particularly troublesome weed in tussock grasslands, also very common in pastures, roadsides, riverbeds, waste places and in many modified open communities.
FL Dec-May.
A fl. of H. perforatum is illustrated in Fig. 54. Of all the weeds in N.Z. pastures that are poisonous to stock, this sp. is one of the most toxic. It causes severe photosensitisation symptoms (Connor 1977).
There is considerable variation within N.Z., but H. perforatum is always distinguished by the following combination of characters: stems erect and 2-lined, sepals without black glands or, if glands present, then irregularly arranged and not marginal, petals with numerous black marginal glands, and lvs lacking black glands. Although the erect flowering stems die in the autumn, the plants have ± prostrate, barren, leafy shoots which remain conspicuous all winter and often form dense mats.
