Hypericum thasium (Nomenclature)
Perennial herb 0.15–0.4(–0.55) m tall, erect from decumbent rooting base, with stems numerous, spreading from taproot, branching from most nodes. Stems 2–4-lined, with amber to reddish sessile glands toward base and few black glands on lines; internodes 10–30(–50) mm, shorter to longer than leaves. Leaves sessile, ascending; lamina 10–35 × 1–4 mm, all linear or lower sometimes lanceolate to narrowly oblong or elliptic-oblong, slightly paler beneath, chartaceous; apex obtuse, margin revolute, base parallel to subamplexicaul; venation: 2–3 pairs of main branches from lower 1/3–2/5 of midrib; laminar glands pale, punctiform, dense; intramarginal glands black, regular, usually hidden. Inflorescence 3–45-flowered, from 1–5 nodes, sometimes with flowering branches from one node below, the whole broadly rounded-pyramidal to cylindric; bracts and bracteoles linear-lanceolate to linear, with margin glandular- or eglandular-fimbriate and with ± developed auricles. Flowers 25–32 mm in diam., buds ovoid, obtuse. Sepals equal, markedly imbricate, basally slightly connate, 7–11 × 2.5–3.5 mm (excluding fimbriae), elliptic to oblong or ovate, rounded, long-glandular- or eglandular-fimbriate; veins 3–5, unbranched; laminar glands pale, punctiform, numerous, and black, few, subapical; marginal glands black, regular. Petals bright yellow, not tinged red, 13–16 × 6–8 mm, obovate-oblong to elliptic-oblong, rounded; laminar glands numerous, pale, linear-striiform (proximal) to mostly punctiform; marginal glands black, punctiform, regular, sessile or in crenations. Stamens c. 45–80, 5-fascicled, longest 8–10 mm, c. 0.5 × petals; anther gland black. Ovary 3.5–5 × 2–3 mm, ellipsoid; styles 5(6), 5(–6.5?) mm, 1.3 × ovary, diverging. Capsule c. 8 × 5 mm, broadly ovoid, with rather sparse, interrupted vittae. Seeds not seen.
Open habitats on sandy or calcareous soil; 0–1000 m.
Greece (Thasos, Thrakia), Bulgaria (E. Rhodope), Turkey (Tekirdağ).
Hypericum thasium, like H. linariifolium (Sect. Oligostema), appears to be most closely related to the narrow-leaved form of H. olympicum (forma tenuifolium), differing from it inter alia by the chartaceous habit, glandular stem, gland-fringed bracts and sepals, and pentamerous androecium and gynoecium. Vegetatively, it shows considerable similarity to luxuriant forms of H. linariifolium, but the inflorescence is quite different.
Apart from the (derived) pentamery in the ovary, H. thasium appears to be a relict species (near?) ancestral, on the one hand, to 2. H. aucheri and, on the other, to the typical species of Sect. Crossophyllum with gland-fringed leaves (3. H. adenotrichum and 4. H. orientale), all of which have anthers with amber glands.