Perennial herb 0.2-0.75 m tall, wholly erect or shortly decumbent but not rooting at base, with woody taproot, usually few-stemmed, unbranched below inflorescence or sometimes with short axillary shoots, wholly glabrous or usually puberulous to densely shortly whitish-pubescent on stems below inflorescence and on both leaf surfaces. Stems green to reddish, terete; internodes all shorter than leaves or upper exceeding them, eglandular or sparsely (along 'lines') to densely black-gland-dotted or shortly black-gland- streaked. Leaves sessile; lamina (5-)10-55 x (3-)5-32 mm, narrowly oblong or oblong-elliptic or lanceolate or rather broadly ovate, paler beneath, thinly chartaceous, not glaucous, glabrous to densely pubescent on both sides, plane, spreading; apex acute to rounded, margin entire, base rounded to truncate or subcordate; venation: (3)4-5 pairs of laterals curved-ascending from lower 0.2-0.5 of midrib, tertiary reticulation dense, not prominent; laminar glands all pale or occasionally some black, dense, unequal; intramarginal glands black, dense but irregular to rather sparse. Inflorescence 5-c. 120-flowered from up to 4 nodes, without or very rarely with 1-2 flowering branches from next lower node, pyramidal or shortly cylindric to corymbiform, lower nodes not distinct, the partial inflorescences nearly always lax-flowered when mature; pedicels 1-4 mm; bracts and bracteoles linear, black-glandular-ciliate, densely glandular-auriculate. Flowers 15-25 mm in diam.; buds cylindric- ellipsoid, obtuse. Sepals (4-)5-6(-8) x 1-1.5 mm, subequal, free or almost so, narrowly oblong to narrowly lanceolate, acute or very rarely subacute, with margin long- to short-glandular-ciliate; veins 5 or 3 with strong near-basal outer branch from each lateral, these sometimes united (commissural) at base; laminar glands all pale to all black, linear at base or all striiform to punctiform; marginal glands black, flat-topped. Petals pale (?) to golden yellow, sometimes veined or tinged red, (8-)10-13(-15) x (2.5-)3-3.5 mm, c. 2 x sepals, oblong-lanceolate, rounded, apiculus absent; laminar glands pale and/or black, scattered; marginal glands absent. Stamens c. 20-40, longest (7.5-)9-10 mm, 0.65-0.8 x petals; anther gland black. Ovary 2-3 x 1-2 mm, narrowly ovoid-pyramidal; styles 6-8 mm, 2-4 x ovary, spreading-incurved. Capsule (4-)5-8 x 2.5-4 mm, ovoid, equalling or exceeding sepals, enclosed when developing by petals twisting together. Seeds dark yellow-brown, 0.6-0.7 mm long; testa linear-reticulate.
2n = 16 (Reynaud, 1980; Strid & Franzen, 1981: 836).
Dry or stony places, in scrub or grassland; 1212m (Sardinia), 300- c. 1330 m (Balkans), 1050-1725 m (Arabia), 1600-3000 m (Ethiopia), 1100-2700 m (East Africa).
Sardinia; Serbia, Macedonia, Albania, Bulgaria; Saudi Arabia (Jebel Fayfa); E. Sudan, Ethiopia (Eritraea to Tigray and Beghemder; Harar); E. Uganda, SW Kenya, N. Tanzania.
H. annulatum is very closely related to H. montanum (q.v. for differences), being its sister species and the basal species of a group comprising the remaining species in sect. Adenosepalum. It varies in pubescence and glandularity over its widely disjunct areas of distribution. The European populations have pubescent stems and leaves and vary in the length of sepal cilia, and they lack superficial or laminar black glands. The northern Ethiopian, Sudanese and Arabian populations show parallel trends north-eastward from Tigray to Arabia in pubescence (sparsely pubescent to glabrous stems and leaves), glandularity (black glands on stem, sepals and petals absent or present) and sepal cilia (long to short). The southern (Harar) plants tend towards the East African population in density of pubescence, in the presence of occasional black glands on the leaves, and (rarely) in having red tinges on the petal veins, but are otherwise like the northern group. The East African population varies in pubescence (stems and leaves densely pubescent to glabrous) and glandularity (black or red glands always on stems and petals, sometimes on leaves and sepals), but the sepal cilia are always long and the petals always red-tinged. The overlaps in variation preclude the recognition of any of these populations at specific level, but three variable subspecies can be distinguished. Subsp. annulatum comprises the European populations, subsp. intermedium most of the north-east African and Arabian populations and subsp. afromontanum the Harar and east African populations.