Small shrub (up to 1.2 m tall) of the Cistaceae family, erect, very branchy and viscous, forming a compact clump. It has subsessile, linear or linear-lanceolate leaves, with three longitudinal veins; flowers with 5 white petals, often spotted with yellow at the base, measuring 9-14 x 6-10 mm, arranged in unilateral cymes, with 2 to 9 flowers per cyme.
Well adapted to hot climates and dry terrain, the species grows in various types of soil, from granite to sandy, including schist, clayey and limestone, and can be found in dry hills, heaths, scrubland and forests with good clearings.
General distribution: Mediterranean region and Macaronesia (Madeira and the Canary Islands).
In Portugal, the species occurs, in addition to the island of Madeira, in the centre and south of the mainland.
Flowering: from April to June.
* Other common names: Sargassum; Dark Sargassum; Terrestrial Sargassum; Outside Rosemary.