Hypericum Decaisneanum

''Hypericum decaisneanum'' is a species of flowering plant in the St John's wort family Hypericaceae. Named for French botanist Joseph Decaisne, it is a small perennial herb that grows mostly upright. It has thick, papery leaves and up to twenty flowers with bright yellow petals. Endemic to the Jebel al Akhdar province of Libya, ''H. decaisneanum'' is found in the cracks of limestone rocks on steep escarpments. It is a member of numerous plant communities and associations of chasmophytes, of which it is sometimes a key species. First described in 1899, the species was originally placed in section ''Taeniocarpium'' of the genus ''Hypericum'', but conflicting relationships have meant it has been treated more recently as a member of section ''Adenosepalum''.

Etymology

The genus name ''Hypericum'' is possibly derived from the Greek words (above) and (picture), in reference to the tradition of hanging the plant over religious icons in the home. The specific epithet ''decaisneanum'' is in honor of French botanist Joseph Decaisne, who had recently died when the first collections of the species were made.

Description

''Hypericum decaisneanum'' is a perennial herb that grows mostly upright and can be tall. The base of the plant can have visible roots, and its taproot is woody. It has many stems, but has no branches below its flower clusters. The stems are covered in whitish-grey hairs, and are green on the upper parts of the plant and reddish on the lower parts. The leaves are crowded together and lack leaf stalks. The leaf blades are an oval shape, long and wide. They are the same color on the top and bottom, and have a thick, papery texture without any waxy coating. They have short hairs on their top side, and more dense hairs on the bottom. The leaf tip sometimes curls and is only somewhat pointed. There is no texture on the edges of the leaf, and the base is blunt. The leaf blades have a dense concentration of pale glands, and sometimes have a few black glands.

The flower clusters have between three and twenty flowers out of 1–4 distinct nodes. There are no flowering branches on the lower parts of the stem; all flowers are in a narrow pyramid-shaped or corymb-like cluster at the end of the stem. The bracts and bracteoles range in shape from stretched ovals to triangular lances, and have dense black glands. Individual flowers are around wide, and are an egg shape when budding. The sepals are long and , but are usually around the same size on a flower. They range in shape from narrow and oblong to wide and elliptic, with a rounded end. They have pale glands in linear patterns, and sometimes several black dots near their end. The petals are bright yellow with red veins, and measure long and wide, or roughly 2.5 times the size of the sepals. They are oblong and have a rounded tip with no apiculus; scattered pale and black leaves may be present on the petals. Each flower has around 40 stamens, the longest of which are long, or just shorter than the petals, and have a black anther gland. The ovary has the shape of a narrow, egg-like pyramid, with styles that are around long and curve inwards. The seed capsule is egg-shaped, and can be larger than the sepals; it is enclosed when it is growing by the petals twisting together.

''Hypericum decaisneanum'' blooms in the late spring and early summer. In general, because of its dense and hairy leaves and the black glands on its petals, the species resembles a smaller form of ''Hypericum annulatum'' subsp. ''afromontanum''.

Taxonomy

The species was originally described by Ernest Cosson and Jules Alexandre Daveau in 1899 as ''Hypericum decaisneanum''. In the description they listed the unresolved name ''H. taubertii'' as a synonym of the species, but did not provide reasoning for the inclusion. Cosson and Daveau placed ''H. decaisneanum'' in section ''Taeniocarpium'' based on their morphological observations. While most species of the genus '' Hypericum'' were included in a monographic study by Norman Robson in the 20th century, ''H. decaisneanum'' was not mentioned. Furthermore, its closest relatives were later addended to the monograph and their infrageneric relationships were discussed.The related species were '' H. formosissimum'', '' H. huber-morathii'', and '' H. minutum''. However, ''H. decaisneanum'' was neglected from these later editions as well. Further complicating the issue was the species' later inclusion by Norman Robson and his colleague David Pattinson within a "''Huber-morathii'' group" inside section ''Adenosepalum'' in the online edition of the monograph in 2013. Under that classification, the placement of ''Hypericum decaisneanum'' was summarized as follows:

'' Hypericum''

: ''Hypericum'' subg. ''Hypericum''
:: ''Hypericum'' sect. ''Adenosepalum''
::: ''Huber-morathii'' group
:::: ''H. decaisneanum – H. formosissimum – H. huber-morathii'' – '' H. minutum – H. sechmenii''

Distribution, habitat, and ecology

''Hypericum decaisneanum'' is endemic to the Jebel al Akhdar province of Libya. It is found in the crevices of limestone rocks at elevations of . In particular, it is found on the north-facing slopes of major escarpments.

The plant communities that ''Hypericum decaisneanum'' belongs to have been the subject of several research endeavors. It has been noted to be part of an association of chasmophytes that centers around '' Micromeria conferta'' and '' Reaumuria mucronata''.The other members of the association are '' Cyclamen rohlfsianum'', '' Rhamnus'', '' Varthemia candicans'' and '' Thymus capitatus''. It is also a part of one species association called "''Athamantion dellae-cellae''",The other members of the association are '' Asperula cyrenaica'', '' Athamanta della-cellae'', '' Daphne jasminea'', '' Erica sicula'', '' Micromeria conferta'', '' Origanum cyrenaicum'', ''Ptilostemon gnaphaloides'', '' Sedum cyrenaicum'', and '' Stachys rosea''. and is a key species in another alliance called "''Sedo micranthi-Hypericetum decaisneani''" along with ''Sedum album'' and other chasmophytes.The other members of the association are '' Micromeria conferta'', '' Stachys rosea'', ''Chiliadenus candicans'', and ''Petrorhagia illyrica''.

Like other species in the ''Huber-morathii'' group, ''H. decaisneanum'' can be cultivated in dry, rocky crevices with poor soil and protection against winter wetness. It can be propagated by seeding in spring under a thin layer of soil, and has a germination period of 1–3 months. Cuttings are typically taken in the late summer. The species is threatened by the uprooting of vegetation, fire, overgrazing, pollution, and gathering.

Notes

References

Bibliography

*
*
*
*
*

decaisneanum
Flora of Libya
Plants described in 1889
{{Hypericum species Navbox