Hypericum calycinum is a prostrate or low-growing shrub

Shrub

A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...

 species of the genus Hypericum

Hypericum

Hypericum is a genus of about 400 species of flowering plants in the family Hypericaceae ....

(Hypericaceae

Hypericaceae

Hypericaceae is a plant family in the order Malpighiales. Molecular data supports its monophyly. Some systematists treat it as a subfamily of the Clusiaceae. When it is accepted as a distinct family, it contains the following genera:* Cratoxylum Blume...

). Widely cultivated for its large yellow flowers, its names as a garden plant include Rose of Sharon

Rose of Sharon

Rose of Sharon is a common name that applies to several different species of flowering plants that are highly valued throughout the world. The name's colloquial application has been used as an example of the lack of precision of common names, which potentially causes confusion...

in Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 and Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, and Aaron's beard, Great St-John's wort, and Jerusalem star.
Grown in Mediterranean climates, widely spread in the Strandja Mountains along the Bulgarian and Turkish Black Sea coast.

Description

It is a low, creeping, woody shrub to about 1 m tall and 1–2 m wide but often smaller. The green, ovate leaves grow in opposite pairs.
The solitary flowers are 3–5 cm in diameter, a rich yellow, with five petals and numerous yellow stamen

Stamen

The stamen is the pollen producing reproductive organ of a flower...

s.
It is indigenous to southeast Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 and southwest Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

. It is a popular, semi-evergreen

Evergreen

In botany, an evergreen plant is a plant that has leaves in all seasons. This contrasts with deciduous plants, which completely lose their foliage during the winter or dry season.There are many different kinds of evergreen plants, both trees and shrubs...

 garden shrub with many named cultivar

Cultivar

A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...

s and hybrids derived from it.

In North America the name Rose of Sharon is applied to a species in a different order, Hibiscus syriacus

Hibiscus syriacus

Hibiscus syriacus is a widely cultivated ornamental shrub in the genus Hibiscus. Common names include Rose of Sharon , Shrub Althea and Rose Althea.-Growth:...

.

This species is capable of producing the medicinally active components of H. perforatum (hyperforin etc.), though in different ratios, with adhyperforin predominating, and a low level of hyperforin present.