Perennial herb 0. 11-0.35(-0.45) m tall, erect to ascending from creeping, rooting and branching base, with herbaceous taproot, usually several-stemmed, unbranched below inflorescence, strigose- pubescent on stems below inflorescence and on both surfaces of leaves. Stems green, terete; internodes exceeding to shorter than leaves, eglandular. Leaves sessile; lamina 12-35 x 9-29 mm, oblong-ovate to broadly ovate, concolorous, thinly chartaceous, not glaucous, equally and rather sparsely hirsute on both sides, more densely so along veins beneath, plane, spreading; apex rounded, margin entire, base rounded to shallowly cordate; venation: 3-4 pairs of laterals curved-ascending from lower 0.25-0.4 of midrib, tertiary reticulation dense, slightly prominent; laminar glands pale, dense, subequal; intramarginal glands black, dense to rather sparse. Inflorescence 4-c. 90-flowered from 1-3 nodes, without flowering branches below, shortly cylindric to corymbiform, dense; pedicels 1.5-2 mm; bracts and bracteoles lanceolate to linear-lanceolate, black-glandular-ciliate, densely glandular-auriculate. Flowers 12- 15(-20?) mm in diam.; buds ellipsoid-subglobose, rounded. Sepals 3-6 x 1-1.5 mm, equal, free, narrowly oblong to narrowly elliptic, acute to subacute, with margin long-glandular-ciliate; veins 3, prominent, outer ones branching; laminar glands pale, striiform to punctiform; marginal glands black, flat-topped. Petals rather pale yellow, 7-9 x 2.5-3 mm, 2.5-3 x sepals, oblong-elliptic, rounded, apiculus absent; laminar glands pale, sometimes few; marginal glands distal, black, immersed or prominent. Stamens c. 20-35, longest 7-9 mm, equalling petals; anther gland black. Ovary c. 2 x 1 mm, ellipsoid; styles 5-6 mm, 2.5-3 x ovary, spreading-incurved. Capsule 4-5 x 2.5-3 mm, broadly ellipsoid, shorter than to exceeding sepals, enclosed when developing by petals twisting together. Seeds dark brown, 0.6 mm long; testa finely reticulate-scalariform.
2n= 16 (Reynaud, 1980).
Damp and shaded places among rocks; 300-1700 m.
Greece (Evvoia, Andhros).
H. delphicum is clearly a derivative of H. annulatum subsp. annulatum, differing from it in the shorter, creeping and branching stems, the rougher indumentum and (apart from the high-altitude form of subsp. afromontanum) the more condensed inflorescence. It has a relict distribution, being restricted to isolated areas in Evvoia and Andhros, and, in turn, is related (ancestral?) to H. athoum.