Hypericum olympicum, commonly known as the Mount Olympus St. John's wort,[2][Note 1] is a species of flowering plant in the family Hypericaceae found in the Balkans and Turkey and introduced to western Europe.

It has been widely cultivated for centuries because of its large, showy flowers, which are far larger than those of most other species in Hypericum.

The bracts are reduced-foliar, are broadly imbricate, and lack black glands, and the bracteoles are similar but smaller in size.

[8][10] The seed capsule is 5–10 by 4–8 millimetres (0.20 in–0.39 in × 0.16 in–0.31 in) and is shorter than the sepals, and is shaped broadly oval-like to spherical.

[9] The species is native to Southeastern Serbia, Macedonia, Albania, Bulgaria, Greece (excluding Crete and western Aegean islands), and northwestern Turkey.

[11][12] The species was first introduced to England in 1676 by Sir George Wheeler from seeds found in Turkey, and it was cultivated at the Oxford Botanical Garden.

[13][5] It can be found in sandy, stony, and sometimes grassy places or among rocks in open ground, or in pine woodland at elevations of 0–2000 m.[11] Because of its large, showy flowers, relative hardiness, and dense shape, the species is valued among gardeners, specifically in the United Kingdom.

[2] While the species is not at all harmful to humans, it can be toxic to dogs, cats, and horses, and should be planted away from such animals.

[14] It can be grown in chalk, clay, sand, or loam, and requires moist ground, but with sharp drainage.

As it requires sharp drainage to prevent winter rot, it is a suitable subject for the rockery or alpine garden.

So-called because of its lemon-colored petals, it is often the plant that is found in home or botanical gardens.

[28] H. olympicum has been studied alongside other Hypericum species for their ability to suppress the growth of cancer in several ways.

It has also been shown to help induce apoptosis in damaged cells because of the genotoxic properties of some of its chemical constituents.