Helianthemum

Helianthemum
Helianthemum nummularium
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Malvales
Family:	Cistaceae
Genus:	Helianthemum Mill.
Species
See text.

See text.

Helianthemum /ˌhiːliˈænθᵻməm/, known as rock rose, sunrose, rushrose, or frostweed, is a genus of about 110 species of flowering plants in the family Cistaceae. They are widely distributed throughout the Northern Hemisphere, especially in the Mediterranean. There are New World species, but it has been proposed that these be transferred to genus Crocanthemum.

These are usually shrubs or subshrubs, and some are annual or perennial herbs. The leaves are oppositely arranged, but some plants may have alternately arranged leaves along the upper stems. The flowers are solitary or borne in an array of inflorescence types, such as panicles, racemes, or headlike clusters. The flower has three inner sepals and two smaller outer sepals. It has five petals usually in shades of yellow, orange, or pink. The style at the center is tipped with a large stigma. The fruit is a capsule containing many seeds.

Helianthemum are known to form symbioses with mycorrhizal fungi. In the Mediterranean they are associated with Terfeziaceae, the desert truffles. Together, plant and fungus may have a beneficial effect on the arid local landscapes, preventing soil erosion and desertification. Some symbiotic pairs include Helianthemum salicifolium and the truffle Tirmania nivea, and H. guttatum and T. pinoyi.

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