Hypericum japonicum

Hypericum japonicum
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Malpighiales
Family:	Hypericaceae
Genus:	Hypericum
Section:	H. sect. Trigynobrathys
Species:	H. japonicum
Binomial name
Hypericum japonicum Thunb. 1784[1]
Synonyms[4]
Brathys japonica (Thunb. ex Murray) Wight H. chinense Osbeck[2] H. jeongjocksanense S.J.Park & K.J.Kim H. mutilum sensu Maxim. Sarothra japonica (Thunb.) Y. Kimura[3]

Hypericum japonicum, known as matted St. John's-wort,^[3] is an annual herbaceous flowering plant in the St. John's wort family Hypericaceae, in Hypericum sect. Trigynobrathys.

H. japonicum is unusually small for a St. John's wort, growing only 2–5 cm (0.8–2.0 in) tall.^[5] Its stems are green and 4-angled, with 2–52 mm (0.1–2.0 in) long internodes that usually exceed the leaves. The leaves are sessile and spreading and are persistent. The species is 30-flowered with flowers branching from up to three nodes.^[6] The flowers are 4–8 mm (0.16–0.31 in) in diameter and their petals are bright yellow or orange. The species' stamens number 5–30 in irregular groups or in five groups when few in number. Its seeds are approximately 50 mm (2.0 in) long.^[4]

The species flowers primarily from October–March.^[7]

The seeds of H. japonicum closely resemble those of the extinct paleospecies Hypericum tertiaerum.^[8]

The species is found across the Indian subcontinent, China, Southeast Asia, and Oceania.^[9] It has been recorded as occurring in Hawaii, however it was determined that this was an error.^[4]