| Hypericum sechmenii | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Malpighiales |
| Family: | Hypericaceae |
| Genus: | Hypericum |
| Section: | Hypericumsect. Adenosepalum |
| Species: | H. sechmenii |
| Binomial name | |
| Hypericum sechmenii Ocak & O.Koyuncu | |
  | |
| Approximate distribution ofHypericum sechmenii withinTurkey[1] | |
Hypericum sechmenii, orSeçmen's St John's wort, is a rarespecies offlowering plant of the St John's wortfamily (Hypericaceae) that is found in theEskişehir Province of centralTurkey. It was firstdescribed in 2009 by Turkishbotanists Atila Ocak and Onur Koyuncu, who named the species in honor ofÖzcan Seçmen, a fellow botanist. They assigned the species to the genusHypericum, andNorman Robson later placedH. sechmenii into thesectionAdenosepalum.
Hypericum sechmenii is aperennial herb that usually grows in clusters of stems 3–6 centimeters (1–2 inches) tall and blooms in June and July. The stems of the plant are smooth and lack hairs, while the leaves are leathery and do not haveleafstalks. Its flowers are arranged in clusters that form a flat-topped shape known as acorymb, and each flower possesses five bright yellow petals. Several species are similar in appearance toH. sechmenii, with only minor physical differences that set them apart. The most closely related of these areHypericum huber-morathii,Hypericum minutum, andHypericum thymopsis.
Found amonglimestone rocks,Hypericum sechmenii has an estimateddistribution of less than 10 square kilometers (4 square miles), with fewer than 250 surviving plants. Despite containingdruse crystals and toxic chemicals that are thought todeter herbivory, the species is threatened byovergrazing from livestock, as well as by other factors likeclimate change andhabitat loss.
Hypericum sechmenii is a floweringperennial herb that grows indense clusters of upright stems typically 3–6 cm (1–2 in) tall,[2] sometimes up to 8 cm (3 in) tall.[3] It has five-petalled yellow flowers[4] that usually flower in June and July.[3]
The outside of the plant's roots is made of a thickcuticle, a protective waterproof covering made of fats and wax. Directly beneath the cuticle are one to two bark-like layers ofperiderm that are composed of several layers of dead cells. Beneath the periderm are several layers of thin-walled cells called acortex. Thetissue of the roots is completely covered in a layer of the water transport tissue found in plants calledxylem.[5]
The numerous smooth andhairlessstems[3] ofHypericum sechmenii have multiple layers of different kinds of cells. On the outside is a thin cuticle that covers a single layer ofepidermis. Beneath this epidermis, there are several layers of oblong peridermal cells. These contain a waxy substance calledsuberin that ishydrophobic. Some cells in the periderm of the stems also containinorganic minerals known asdruse crystals,[6] which a 2020 paper theorized might deterherbivory because of their toxicity.[7] Beneath the periderm is the main growth tissue, thevascular cambium, which produces xylem and the transport tissue found in plants calledphloem.[6]
Theleaves ofHypericum sechmenii lackleafstalks, instead attaching directly to the stems. They are roughly 0.2–0.5 cm (0.08–0.2 in) long,[2][3] and densely overlap each other. The texture of the leaves is described assubcoriaceous, or somewhat leathery. The shape of the leaves is either egg-like (ovate) with a broader base, orelliptic with rounded tips and pointed bases (cuneate). There are numerous paleglands on the surfaces of the leaves, and a few black glands can be found on theiredges.[3] The black glands are large enough to be seen by the naked eye, but to see the pale glands the leaf may need to be held up to a light. In the type species of the genus,H. perforatum, the pale glands contain and excreteessential oils, while the black glands contain red-stainingphenolic compounds (anthraquinone derivatives) that deter some herbivorous insects.[8] On the top and bottom sides of the leaves there are pores (stomata) that regulategas exchange, and there is tightly packedphotosynthetic tissue just below the epidermis. Some of the cells in this tissue also contain druse crystals.[9]
Hypericum sechmenii usually flowers from June to July, and it fruits in July.[3] The flower clusters known asinflorescences grow on the ends of the stems and typically have three to five flowers each. The flowers are arranged such that there are longer flower stems (pedicels) on the outer flowers than on the inner ones. This gives the cluster a flat top and forms a structure called acorymb. The specializedbract leaves, which surround the flowers, are long and have glands and small hairs calledcilia. The leafy structures that provide support for the petals, called thesepals, are roughly 0.2 cm (0.08 in) long, are an oblong shape, and can either be pointed or rounded. Their edges also have glands and small hairs, similar to the bracts. However, they may also haveamber-colored dots and lines, which the bracts lack.[2][3] The petals are yellow, like the type species ofHypericum,[10] and grow in a pentagonal arrangement on each flower.[4] They are 0.4–0.7 cm (0.2–0.3 in) long and have amber-colored glands that are shaped like dots or short lines. On the edges of the petals there are a few black glands in addition to the amber-colored ones.[2][3]
Thepollen grains ofHypericum sechmenii have three grooves in a triangular layout, and the overall shape of the grain is a slightly elongated sphere. An individual grain is17.2micrometers (μm) long and11.5 μm wide. Each surface groove is12.2 μm long and2.4 μm wide, and the space where the grooves meet is1.7 μm in diameter. There are pores on the surface of the pollen that are2.5 μm long and2.2 μm wide. Surrounding the grain is a tough outer wall that is1.5 μm thick and has an outer layer with a net-like pattern.[11]
Theseed capsules are 0.3–0.4 cm (0.12–0.16 in) and oblong, and theirovaries have a few oil cavities that run lengthwise along the capsule. The seeds themselves have tiny, regularly spaced pits that form patterns similar in appearance to small lines or ladders.[3]
Hypericum sechmenii is similar in appearance to other Turkish species ofHypericum. In its original description, its similarity toHypericum huber-morathii andHypericum minutum was noted, and it has also been compared toHypericum thymopsis.[3][12]
When compared toHypericum minutum andH. huber-morathii,H. sechmenii has differences in its leaves, flowers, and pollen grains. Its leaves are adjacent to one another on the stem and overlap, while the leaves ofH. minutum andH. huber-morathii are placed on opposite sides of the stem and do not.H. sechmenii has more flowers on an inflorescence (3–5) thanH. minutum (1–3), but usually has fewer thanH. huber-morathii (3–12). The glands on its petals are also different;H. sechmenii has amber-colored dots and lines, whereasH. minutum has amber-colored dots with no lines andH. huber-morathii only has black dots or no visible glands at all. Pollen grains are another way to tell the three species apart.H. minutum has tiny protrusions on the surface of its pollen called microspinae, whichH. sechmenii lacks, andH. minutum also has far fewer distinct grooves on its surface.H. sechmenii pollen grains are larger than those ofH. minutum and smaller than those ofH. huber-morathii.H. huber-morathii has a slightly larger region on the end of the grain where the grooves meet.[13]
Anatomically,Hypericum sechmenii is also similar toH. thymopsis despite not being as closely related. Both species have similar stomata that make them able to thrive in dry climates, and both have stomata on the upper and lower sides of their leaves. However, the structure of the species' stem tissue sets them apart.H. sechmenii has a thinner layer ofpalisade tissue and its inner stem region is made up solely of xylem, whereasH. thymopsis has softer, spongypith tissue as well.[12]
Hypericum sechmenii was first observed and collected by the Turkish botanist Atila Ocak in 2006. Theholotype of the species was collected in that same year by Ocak in the district ofGünyüzü and is now housed atEskişehir Osmangazi University.[3][14] Three years later, in December 2009, the species wasformally described by Ocak and Onur Koyuncu in thejournalAnnales Botanici Fennici. The authors gave the species thespecific epithetsechmenii as an homage to the prominent Turkishtaxonomist andecologistÖzcan Seçmen. InTurkish, the plant is calledseçmen kantaronu, translated as Seçmen's St John's wort.[15][3] The species was incorporated into theFlora of Turkeyendemic species registry in 2011 alongside another recently describedHypericum species,Hypericum musadoganii.[16]
In 1977, the British taxonomistNorman Robson began amonograph of the entire genusHypericum. He divided the genus into 36sections, with almost every species in the genus placed into one of these sections based on theirmorphology and early applications ofmolecular phylogenetics.[17] However,Hypericum sechmenii was not included in this original monograph, as it had not yet been identified as a unique species. Robson later corroborated the findings of Ocak and Koyuncu thatH. sechmenii was its species, taking note of its similarities to other Anatolian species ofHypericum, specificallyHypericum minutum andHypericum huber-morathii. Because of this, Robson placed the species in aclade called theHuber-MorathiiGroup. The group comprises five Turkish species ofHypericum and lies within the large sectionAdenosepalum. The placement ofH. sechmenii was summarized by Robson as follows:[2]
Hypericum sechmenii is one of around 45 species ofHypericum that areendemic to Turkey.[18] Specifically, the species has been found in central Turkey withinEskişehir Province,[15][19] at two separate localities: one near the peak ofArayit Mountain, and the other between the towns ofKaymaz andSivrihisar.[2][3] The area of distribution on Arayit Mountain is estimated to be 2 km2 (0.8 sq mi). The area of the Kaymaz to Sivrihisar locality is estimated to be smaller.[20]
The species' habitat is usually in and among the crevices oflimestone rocks andoutcroppings. The general elevation of the species is 1,750–1,820 m (5,740–5,970 ft).[2][3] Several other specimens ofHypericum sechmenii have been collected since the species' discovery and are preserved at various Turkish herbariums.[21]
| Type | District | Locality | Habitat | Collection Date | Herbarium | Reference |
|---|---|---|---|---|---|---|
| Holotype | Günyüzü | Arayit Mountain | Rock crevices | 10 June 2006 | Eskişehir Osmangazi University | [22] |
| Isotype[note 1] | Günyüzü | Arayit Mountain | Rock crevices | 10 June 2006 | Gazi University | [21] |
| Isotype | Günyüzü | Arayit Mountain | Rock crevices | 10 June 2006 | Hacettepe University | [21] |
| Sivrihisar | Arayit Mountain | Hilly steppe | 7 July 2011 | [4] | ||
| Sivrihisar | Sivrihisar–Kaymaz | Rocks near Kaymaz | 13 July 2011 | [4] | ||
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The leaves ofHypericum sechmenii containxeromorphic stomata, pores that have adaptations to allow the plant to better survive in itsarid, steppe habitat ofCentral Anatolia,[23][24] defined as theIrano-Turanianfloristic region.[25]H. sechmenii has two adaptations of the genusHypericum that deter grazing. The first is the presence of numerous black glands on the leaf margins; in other species ofHypericum, similar glands have been shown to contain compounds that aretoxic to creatures consuming the plant.[8] The second is the presence of druse crystals in cells of the stem and leaf tissue.[6] These contain minerals that are thought to deter some insects from grazing.[7]
Hypericum sechmenii grows alongside small shrubs and perennial herbs like stonecress (Aethionema subulatum), woodruff (Asperula nitida), harebell (Asyneuma compactum), small toadflax (Chaenorhinium minus), Kotschy's damask flower (Hesperis kotschyi), flax (Linum cariense), restharrow (Ononis adenotricha), dandelions (Scorzonera tomentosa), Turkish catchfly (Silene falcata), and wood betony (Stachys lavandulifolia). It is found among only one otherHypericum species, that beingHypericum confertum.[26]
Propagation ofHypericum sechmenii is undertaken by planting seeds in the spring, barely covering them in soil. They are then allowed to germinate for 1–3 months at a temperature of 10–16 °C (50–61 °F). The plants grow best in sunny, dry rock crevices with protection from winter dampness. The division is done in the spring, whilecuttings are taken in the late summer.[27]
The species is rare, with an estimated 250 surviving plants of the species in an area assumed to be smaller than 10 km2 (4 sq mi). The species is under threat from bothabiotic factors, especially climate change, as well ashuman impact from agriculture and the grazing of domesticated animals. Because of these threats and the unsustainably small population size ofHypericum sechmenii, biologists from the Eskişehir Osmangazi University recommended that the species be classified asCritically Endangered by theInternational Union for Conservation of Nature, although no conservational measures had been taken as of 2013[update].[20]