The genus Dionysia –Dionysos alpine cushions
Current climate change is rendering Dionysia plants extremely vulnerable. Rising temperatures and dryer climates are stressful for highly specialised Dionysos alpine cushions. They can only escape upwards in principle and when the mountain reaches its limit, they perish. Conservation projects with replanting are not possible. All that remains is so-called "ex situ" conservation, that is, cultivation of which our collection is a shining example.
Plants that like extremes
Dionysos cushions constitute a group of primrose relatives that have adapted themselves to living on vertical cliff faces, some even in cave mouths. They are exposed to very bright sunlight, UV radiation, extreme changes of temperature, hard winds and summer drought. They seek water deep in the microscopic crevices of limestone mountains. Water management in such a situation is a critical factor that they handle via their cushion-like growth, their waxy, fuzzy or sticky-haired aromatic leaves, or by avoiding all-too-exposed locations. Their natural habitats are in south-western and central Asia, mainly Iran and Afghanistan. Isolated species also grow in Turkey, Iraq, Oman, Pakistan, Tajikistan and Uzbekistan.
Botaniska's tradition was initiated in the 1960s by the then Director, Per Wendelbo, who was a specialist on south-western Asia's flora. His doctoral thesis (1961) was entitled "A Monograph of the Genus Dionysia" and included 28 species of this genus. As the roads in the region have improved, new species have been discovered, so in his "The Genus Dionysia, a synopsis and five new species" (2007), Botaniska's curator Magnus Lidén names 49 species. Two per cent of them have only recently been named. Many of the species are only known to exist in extremely limited areas, sometimes only one cliff face. We are certain that new species are going to be discovered.
Our collection contains 35-40 species and is used as a refence collection, among others by Magnus Lidén, the current world authority on Dionysia. The Gothenburg Botanical Garden participated in two trips to Iran in the early 2000s, and witnessed the discovery of four new species.
Botanical big game
Although difficult to cultivate, alpine cushions are cloaked with golden yellow or purple, fragrant flowers during the spring. They rank as one of the greatest challenges a grower can meet. An exclusive group of specialists in Central Europe and Great Britain have succeeded in conserving about 40 species in cultivation since the 1960s.
Cultivation and proliferation in Botaniska
Dionysia are recognised as being difficult to grow, and a plant rarely lives longer than 10 years. We conserve and develop our collection by assiduously taking cuttings and exchanging them with other specialists. For home-harvested seeds we must have specimens with both types of "pin", a paintbrush with a single flattened hair and a steady hand.
Dionysia are heterostylous, just like our Swedish primroses. This means that they have two different types of flower – some have a longer pistil and short stamens, and others have a short pistil with long stamens closer to the opening of the crown. Both types prefer pollen from the other type to create seeds and prevent inbreeding.
Most of the cushion species have seed pods with few but quite large seeds some of which remain in the cushions after maturing. What it is that spreads the seeds out over the vertical naked cliffs that they conquer is still uncertain. The larger species produces a wealth of tiny seeds that are spread by wind and weather.
Dionysia are cultivated in a substrate mostly consisting of volcanic products, clay granules and sand – in clay pots sunk into a sand bed. Plant food is supplied by watering. Even though many Dionysia can stand the cold down to minus 15°C, we keep the collection frost-free and allow them plenty of extra lighting. We are testing new, energy-saving, high effectivity LED lighting with good results.
Specialists on Dionysia
The Gothenburg Botanical Garden's horticultural curator Henrik Zetterlund is a specialist on Dionysia, and he tells us why this genus fascinates him:
"Naturally it's the purely scientific aspect, but also that they're the most difficult plants to grow if one wants to devote oneself to working with alpine plants. They also grow in very exciting places. Last but not least, they are so incredibly beautiful!"
Marika Irvine is the gardener in Botaniska responsible for the propagation section, where she works with Dionysia among other plants.