Hypericum androsaemum

A single stem with foliage and flowers

The leaves are arranged in opposite pairs without stipules and lack petioles.[1]The leaf blade is 4–12 cm (1.6–4.7 in) long by 2–8 cm (0.79–3.15 in) wide.[2] The leaves lack hairs on either surface and have small oil glands across their surface.[2] When these glands are crushed, they give off a pungent aroma and leak red pigment. [3] There are other translucent glands that are dispersed throughout the mesophyll at differing depths.[4] There are four or five symmetrical pairs of main veins along the leaf that point in the direction of the tip.[2]

Different angles of the small inflorescence

Hypericum androsaemum has between one and eleven flowers on an inflorescence, which has the form of a cyme and a corymb-like arrangement. There are never accessory flowers, but there are sometimes one to three flowering branches from the lower node. The pedicel stems are 8–14 mm long, with small lance-shaped bracts.[2]

The flowers are 15–25 mm in diameter and have globe-shaped buds. The sepals are very unequal in size, about 6–12 mm long by 3–7 mm wide in an egg shape. The flower petals are a bright golden yellow without the red tinge that is present in the foliage. They curve inward and have an egg-like shape. The stamens are arranged in five fascicles of twenty to twenty-five stamens the longest of which are 7–11 mm long. The ovaries measure 4–5 mm long and 3.5–5 mm wide in the shape of a rough globe.[2]

The berries of H. androsaemum turn black after maturity

The berries of the plant turn from red to a unique black color not found in any other Hypericum species, which is caused by a xanthone present only in Hypericum androsaemum.[5] Another unique characteristic of the species' berries is that they remain fleshy and mostly soft when they ripen, instead of hardening and drying out like other related species.[5] The berries measure 7–12 mm long and 6–8 mm wide with thin casings. The seeds inside are a reddish-brown color.[2]

Hypericum androsaemum has a well-studied phytochemical profile as a result of its use as folk medicine and an herbal supplement. More than eighty essential compounds have been identified from its leaves. The total density of essential oil has been recorded as high as 0.34%. Several different sesquiterpene hydrocarbons dominate the profile, and intermediate and long chain alkenes are highly present. Less prolific compounds include caryophyllene and gurjunene.[6] Many of these essential oils and other phenolic compounds are present in higher quantities while the flowers are still growing.[7] While less studied than the leaves of the plant, the berries of H. androsaemum are rich in chemical constituents as well. Many of these constituents are found in higher densities (or only) while the fruits are red. The most present chemicals are chlorogenic acid, shikimic acid, rutin, epicatechin, and hyperoside.[5]

The genus name Hypericum derives from the Greek words hyper, meaning above, and eikon, meaning picture. This refers to the practice of hanging the flower "above pictures" to ward off evil spirits. The specific epithet androsaemum comes from the Greek word androsaemus, which was used to describe plants with red sap. It is a combination of the words andros, meaning man, and haima, meaning blood.[9] The common name tutsan is French in origin, and derives from the phrase tout-saine, which means heal-all, in reference to the plant's medicinal properties.[3] Its alternative name sweet-amber is in reference to the ambergris-like aroma that is emitted when oil glands on its leaves are crushed.[10]

While Hypericum androsaemum is the most well-known plant named tutsan, other species share that common name. For example, H. xylosteifolium is called "Turkish tutsan" and H. hircinum is called "Stinking tutsan".[7]

The species in Hortus Eystettensis. The inscriptions read (from left to right): Androsaemum foeditum seu Tragôdes, Siciliana, Hÿpericon.

Hypericum androsaemum was known and studied long before the modern system of taxonomy was developed. For example, tutsan was depicted in the 1640 volume of Hortus Eystettensis, a revolutionary book of botanical illustrations. In the codex, the plant was noted to be from Sicily, of the grouping Hÿpericon (a pre-Linnean version of Hypericum), and called "Androsaemum foeditum" or "Tragôdes".[11] The species was first formally described in the modern system by Carl Linnaeus. He described the species as Hypericum androsaemum in the second volume of his Species Plantarum in 1763 alongside around twenty other Hypericum species. Compiling several brief notes from other authorities, Linnaeus gave the following description for the plant:[12]

In the same entry, Linnaeus noted the species' presence in England and its tendency to be found around fences.[12] This original description and type specimen analysis by Linnaeus remains the basis for the modern definition of the species. However, since that original description numerous illegitimate synonyms have been created for various reasons. In fact, while there is now solid consensus that H. androsaemum belongs within the genus Hypericum,[13] it was placed into a separate genus called Androsaemum as recently as 1893.[14]

In 1796, the garden of Chapel Allerton published a list of their plant specimens, noting Hypericum androsaemum as being in their collection, along with the fact it had been described by Linnaeus. However, they still applied two superfluous names (Androsaemum floridum and Hypericum floridum) to their specimens;[15] these names were never accepted as legitimate.[16] Only one validly published heterotypic synonym for Hypericum androsaemum has arisen since its original description. In 1785, Carlo Allioni published a description of a specimen he called Androsaemum officinale, without referencing Linnaeus' original description of Hypericum androsaemum. Still, the description corroborated with the one given by Linnaeus and there is consensus that the specimen Allioni observed did, in fact, belong to Hypericum androsaemum and was not a separate species.[17]

The status of Hypericum androsaemum was definitively resolved with Norman Robson's comprehensive monograph of the genus Hypericum in 1996. Robson established 36 sections within the genus which grouped together very similar species. He designated H. androsaemum as the type species of sect. Androsaemum and clarified its lectotype specimen. Because the actual type specimen that Linnaeus analyzed was not preserved, Robson selected an illustration from Hortus Cliffortianus, which Linnaeus would have at least seen, to serve as the lectotype for the species.[2]

Hypericum androsaemum exhibits a great deal of variation in appearance, especially in cultivation. When this variation is deliberately brought out through selective breeding, the resulting forms are called "cultivars"; however, when populations develop unique traits on their own while in cultivation, those populations can be described by a legitimate botanical name. In the case of H. androsaemum, two such names have been given: H. androsaemum var. aureum has yellow-green leaves, and H. androsaemum f. variegatum has variegated leaves.[2]

In the wild, H. androsaemum exhibits a similarly wide range of physical traits. Larger-flowered plants tend to have red-tinted leaves and larger fruits; smaller-flowered plants have greener leaves and smaller fruits. These traits are not binary, though, and there is a continuous spectrum of forms that link those two extremes wherever they are found. Thus, no legitimate names are given to any of these forms.[2]

Hypericum androsaemum is similar in appearance to the other species in section Androsaemum. It can be told apart from H. foliosum and H. × inodorum by its shorter styles, the unique black color of its ripe berries, and that its petals are never longer than its sepals.[2] In addition to the species of section Androsaemum, it is highly similar to Hypericum xylosteifolium, the sole species in section Inodorum. The most apparent morphological difference between it and H. xylosteifolium is that the seed capsules (berries) of the latter species dry completely when they are mature, whereas those of H. androsaemum remain soft and fleshy.[7] The berries of H. androsaemum only dry if they are left on the plant for around a month after ripening, and will begin to wither at that same time.[2]

• Comparison of inflorescences of related species
• 
  H. foliosum
• 
  H. × inodorum
• 
  H. androsaemum

The species has a wide native distribution, but is most densely found in Western Europe. It is particularly abundant across the British Isles (except for in the Scottish Highlands), in the Ardennes forest of Belgium and France, and on the western French coast. Other European populations include the Pyrenees Mountains, across northern Spain and Portugal, and around Genoa and parts of central Italy. Scattered sightings have been reported through Germany and as far north as Denmark, as well as in Switzerland, Austria, and the Balkans. Outside of Europe, H. androsaemum is found in northern Turkey, the North African coast, the Caucasus, and Iran. While it may have at one point been native to the island of Corsica, it is now believed to be extinct there.[2]

Hypericum androsaemum has become naturalized or invasive in regions to which it is not native. In Australia, it is densely found in the Otway Ranges, South Gippsland Hills, Dandenong Ranges, the Blue Mountains, and in the area around Mansfield. There are also a few scattered populations on Tasmania, but it is not troublesome there. In New Zealand, it is found on both islands frequently enough to be an encroaching weed.[3]

In the late 19th century, H. androsaemum was a popular ornamental plant, leading to its widespread dispersal in non-native regions. While its seeds don't have any special properties that increase their potential for dispersal, they are small and extremely numerous. This allows the seeds to easily contaminate cargo, animals, clothing, vehicles, or other transported items. The species was invasively introduced to Australia in 1865 via the Royal Horticultural Society's botanical garden in Hobart, apparently for use as an ornamental species because of its reddish leaves and bright yellow flowers. In New Zealand, the primary method of invasive dispersal is reportedly by birds.[3]

In 2008, Landcare Research began investigating the feasibility of a biological control for the species. The seed and leaf-tip eating moth Lathronympha strigana and the leaf-feeding beetle Chrysolina abchasica were tested and found to be sufficiently host specific and not a risk to native plant species. As of February 2017, moths were released at 30 sites around the central North Island in New Zealand; however, the beetle is more difficult to rear in captivity, so only one release has been made so far.[19]

When cultivated, Hypericum androsaemum requires minimal maintenance. The species is generally pest and disease free, and is deer resistant.[20] However, it can be prone to nematodes which cause root rot; pest insects such as thrips and scale have been noted. Additionally, in hot and humid climates the species is susceptible to wilting and unrelated root rot.[10] It is tolerant of moderately acidic and alkaline soils, and can withstand drought and freezing temperatures down to -20° C (-4° F). While the plant performs best if spaced roughly 90 cm (3.0 ft) apart from others, it will self-sow via seed in its area if allowed, creating ground cover. After the plant has lost its leaves in the fall, it can be cut back if needed and will regrow from the base in the spring.[21]

Most Hypericum species are difficult to germinate because of heavy seed dormancy. Hypericum androsaemum exhibits both physiological dormancy and chemical dormancy, meaning that seed germination can be kickstarted by both physical and chemical factors. In particular, room-temperature water or the plant hormone gibberellic acid are most effective at bringing its seeds out of a dormant state.[22]

New specimens are propagated by sowing non-dormant seeds in a 10°C (50°F) greenhouse in the spring under a very light layer of soil. Once the seedlings are large enough to handle (after 1–3 months), they are moved into individual pots. After the last frost of winter, the new plants are moved to their permanent outdoor locations. As an alternative method to seed propagation, cuttings of semi-hard wood 10–12 long are sometimes taken in the fall. These cuttings are then placed in a frame for the remainder of the fall and winter, and can be replanted the following spring.[21]

Hypericum androsaemum 'Albury Purple'

Hypericum androsaemum 'Glacier'

In order to combat the invasive tendencies of Hypericum androsaemum, triploid clones of plants with desirable characteristics have been developed by several herbariums.[23] These triploid specimens have been shown to have massively reduced male fertility and complete female infertility; in addition, they still produce the large and colorful fruits for which H. androsaemum is known, and at rates similar to regular diploid plants. [24]