Perennial herb or subshrub, c. 0.15-0.2 m tall, erect from woody taproot or decumbent at base and rooting, often with short ascending branches below inflorescence, the whole plant up to the inflores- cence densely white-puberulous. Stems green to purplish red, terete, internodes mostly shorter than leaves. Leaves sessile, markedly tetrastichous; lamina 7.5-c. 13 x 1.5-4 mm, narrowly oblong to (upper) triangular-lanceolate, concolorous, chartaceous, appearing greyish blue but not glaucous, plane, spreading; apex obtuse, margin plane, entire, base rounded to subcordate; venation: 2 pairs of laterals curved-ascending from lower c. 0.25 of midrib, tertiary reticulation not seen; laminar glands pale, dense, unequal, not prominent; intramarginal to submarginal glands black, rather sparse. Inflorescence (l-)5-c. 11 -flowered, from 1(2) nodes, subcorymbiform to rounded-pyramidal when flowers numerous, rather lax, without lower flowering branches; pedicels 3-7 mm in fruit, with prominent reddish glands; bracts not auriculate; bracteoles linear-lanceolate, with margin black-glandular-ciliate. Flowers c. 25 mm in diam.; buds ellipsoid, acute. Sepals 3.5-4 x 0.8-1.2 mm, equal, narrowly lanceolate, acute to subaristate, irregularly glandular-ciliate or with prominent sessile glands; veins 5, outer branched; laminar glands pale, linear to striiform and (toward margins) black, punctiform to striiform; marginal and apical glands black, smaller. Petals golden yellow, not red-tinged, 9-10(7-12) x c. 4.5-5 mm, c. 2.5 x sepals, oblong-obovate, truncate, with apiculus obtuse, short; laminar glands distal, pale, shortly striiform to punctiform and black, elongate-punctiform, toward apex, marginal or inframarginal glands black, few, elongate-punctiform. Stamens c. 40, clearly 3-fascicled, longest 5-6 mm, c. 0.6 x petals; anther gland black. Ovary c. 2 x 1.5 mm, ovoid-pyramidal; styles 3, c. 4 mm long, c. 2 x ovary, widely spreading. Capsule 4.5-5 x 3-4 mm, ovoid-cylindric, exceeding sepals, enclosed by petals twisting together. Seeds dark red-brown, 0.7 mm long; testa finely scalariform-reticulate.
Shady rock crevices; c. 1 800 m.
Saudi Arabia (Asir).
H. collenettiae is intermediate geographically and in most respects morphologically between H. somaliense and H. sinaicum. As in H. somaliense, the stems are erect and apparently not rooting; the leaves and indumentum are nearer those of H. sinaicum, as is the relatively lax and few-flowered inflorescence. In having black laminar petal-glands it also resembles H. sinaicum, but in its red-glandular pedicels it is nearer to H. somaliense. The prominence of these glands, however, distinguishes it from both species.
H. collenettiae is known as yet from only two populations and is therefore, like H. somaliense, a relict species. According to Mrs Collenette (verb. comm.), the Baljurshi population may no longer exist.