OROSTACHYS Fischer, 1809
Distribution : Tadshikistan, Kirgizia, Kazakhstan, Pakistan (Karakorum), Mongolia, China, Russia (Siberia), Korea, Japan; from sea level(in Japan) to 4400 m alt.
Etymology : The name is composed of the Greek words oros = mountain and stachys = spike, referring to its mountainous habitats and its characteristic inflorescence.
The genus is subdivided like this :
1. Section Orostachys : Leaves of flowering stems ± densely arranged, inflorescences thyrsoid-racemose to paniculate, densely flowered, secondary bracts usually present, 10 stamens.
1a Subsection Orostachys : Leaves blunt = without spines
1b Subsection Appendiculatae : Leaves cuspidate = with spines or appendages.
According to recent DNA results the two subsections are not closely related.
2. Section Schoenlandia : Inflorescences loosely flowered racemes, 5 stamens alternating with the petals.
Depending on authors there are up to 30 species recognized. H. Ohba in IHSP (2003) accepts 12 species:
1a : O. cartilaginea, chanetii, fimbriata, japonica, spinosa, thyrsiflora.
1b : O. boemeri, malacophylla, paradoxa.
2 : O. aliciae, schoenlandii, stenostachya.
Orostachys species are closely related to Sedum – at one time they were considered a section of Sedum – but differing in the often cartilaginous-tipped leaves in dense rosettes and flowers in dense panicles. The first Orostachys species has been described by Linné as early as 1753 as Cotyledon spinosa, the generic name has been proposed some time later by Fischer (1809).
Most of them are biennial plants, but also annual and perennial forms are found. In the first year they produce a rosette, the second year the rosettes elongate to form the inflorescence - the smallest not exceeding 5 cm in height, the tallest up to 50 cm ! It will flower in the following year and die after the seeds have ripened = plants are monocarpic. In Asia they are flowering in August, in Europe most of them are autumn flowering. The flowers are 5- (6-)merous and petals are white, pink, greenish or yellowish. Some species produce offsets while others can only be propagated from seed.
Species of C Asia are adapted to a strictly continental climate = short and very hot summers and long winters with temperatures down to – 40° C. This means that plants of Section Orostachys are considered as fully hardy in Europe but should be kept on the dry side during winter. Anyway they should be grown in a very well draining soil mix and also in summer be watered only moderately. O. spinosa is probably the most hardy species, growing in regions with summer temperatures up to + 60° C and winter temperatures down to – 60° C.
In East Asian countries Orostachys are often grown on roofs – similar to Sempervivum in Europe.
Orostachys species in cultivation hybridise freely, so most of the plants in collections / being offered will be hybrids.
References :
- IHSP 2003
- Crassulaceae (stonecrops) of Siberia and the Russian Far East : Orostachys by S. B. Gontcharova and A. G. Beluha, in Avonia 29 (1) 2011
Margrit Bischofberger