The genus Hypericum contains approximately 500 species which are divided into 36 sections as described by botanist Norman Robson. This division into distinct sections is largely due to the fact that a genus-wide monograph was performed by Robson in 1977, which allowed for a comprehensive analysis of the genus's taxonomy. A phylogenetic study was more recently completed for the genus, which gave evidence to suggest that the genus Triadenum is a clade within Hypericum and that the genus Thornea is sister to Hypericum. In addition, the study found that about 60% of the sections of Hypericum are monophyletic. Almost all species of Hypericum are either perennial herbs, shrubs, or small trees, but the genus also contains a small amount of subshrubs and annual herbs. Most of its species contain hypericin or hyperforin and some are used for their healing properties in folk medicine. The species' leaves are always placed opposite, and are normally decussate. Their flowers are generally homostylous, but very few are dimorphically heterostylous. The petals are normally golden yellow or orange, but some are white or cream, and are veined dorsally. They have 4–5 stamen fascicles, 2–5 ovaries, and 2–5 styles. Some species grow capsular fruit which are colored red or blackish. Hypericum species can be found all over the world in temperate to tropical areas. The genus is most diverse in Turkey (~80 species) and China (~60 species), but can be found across Asia and Europe, in parts of Africa and South America, Australia, and across the United States and southern Canada. Non-native species have also been introduced into various regions of the United States and Argentina. The genus are generally found in dry, desert areas to being in shallow water, and can be found from warm temperate climates to cold temperate climates. Some Hypericum species are used as ornamental plants because of their large, spreading flowers. These include H. aegypticum, H. androsaemum, H. calycinum, and H. olympicum. In addition, there are a number of hybrids and cultivars that have been developed for use in horticulture. Some notable cultivars are H. × moserianum, H. 'Hidcote', and H. 'Rowallane'. Several species are also used for their medicinal properties, especially their ability to alleviate mild clinical depression, by drawing out the oily extract from the flowers. H. perforatum is the most potent out of all the species, and is the only species cultivated commercially for herbalism and medicine.
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Sect. Adenosepalum Adenosepalum Spach is divided into four subsections: Adenosepalum, Aethiopica, Caprifolia, and the Huber-Morathii Group. These subsections contain eight, seven, eleven, and five species, respectively, giving the section Adenosepalum a total of thirty-one species. In addition, Adenosepalum contains two Nothospecies: H. × joerstadii and H. pubescens × tomentosum. H. annulatum has three distinct subspecies. Adenosepalum is made up of primarily perennial herbs, and also includes shrubs and shrublets. Its species grow to be approximately 2.5 meters tall, and are generally deciduous. Species in Adenosepalum are glabrous or have simple hairs, and almost always have dark black glands on their leaves, sepals, and rarely on their petals and stems. Their leaves are placed opposite and have no ventral glands. Their flowers are stellate or homostylous. They have 5 sepals, 5 stamen fascicles, and 5 petals.
Sect. Adenotrias Adenotrias (Jaub. & Spach) R. Keller contains three species: H. aciferum, H. aegypticum, and H. russeggeri. Its type species is H. russeggeri. It is not divided into any subsections. H. aegypticum has three subspecies: H. aegypticum aegypticum L., H. aegypticum maroccanum (Pau) N.Robson, and H. aegypticum webbii (Spach) N.Robson. Adenotrias contains shrubs and shrublets. Its species can grow to be up to 2 meters tall. Its species are glabrous, but have no dark glands. Their leaves are lined and glandular, and are cortex green. Their flowers are almost tubular, and are heterostylous. They have 5 sepals, 5 petals, and 3 stamen fascicles.
Sect. Androsaemum Androsaemum (Duhamel) Godron contains four species: H. androsaemum, H. foliosum, H. grandifolium, and H. hircinum. In addition, Androsaemum contains one Nothospecies: H. × inodorum. It is not divided into subsections. Its type species is H. androsaemum. One of its species, H. grandifolium, has five different subspecies. The section's species are often collectively referred to as Tutsan. Androsaemum contains shrubs that grow to be from 0.3–2 meters tall. Its species are deciduous and glabrous, but have no dark glands. Their leaves are opposite, decussate, free, and are a pale color. Every species has 20 flowers, branching out from 2 separate nodes, which are homostylous. They have 5 sepals, 5 petals, and 5 stamen fascicles.
Sect. Arthrophyllum Arthrophyllum Jaub. & Spach contains five species, and is not divided into any subsections. Its type species is H. rupestre. Arthrophyllum is most closely related to Webbia. Arthrophyllum contains shrubs that grow to be approximately 0.9 meters tall and are deciduous but never leafless. Species in Arthrophyllum are glabrous, with reddish to dark glands. Their leaves are placed opposite and are either decussate, sessile, free, or perfoliate and have no ventral glands. They are 40-flowered, and their flowers are stellate and homostylous. They have 5 sepals that lack marginal glands. Arthrophyllum's species also have 5 petals and 3 stamen fascicles, each with 20–40 stamens. Their seeds are narrow and cylindrical.
Sect. Ascyreia Ascyreia Choisy contains about 50 species and also includes four nothospecies. The section is one of the largest in the genus that is not divided into any subsections. Its type species is H. calycinum. The section is synonymous with Norysca Spach.. Ascyreia is made up of mostly shrubs or shrublets, but also contains a few trees. Its species generally grow to be from 4–5 meters tall. Some of the species are evergreen, but most are deciduous. They are glabrous, and lack dark glands. Their leaves are opposite, decussate, and free. The section's species have anywhere from 1–25 flowers, which are stellate and homostylous. They have five sepals, which are free. They also have five petals and five stamen fascicles, which each have 20–100 stamens. Their seeds are cylindric or ellipsoid, and some are laterally winged.
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