Monday, 13 March 2017

Pleione Orchids

One of my interests has always been odd or unusual plants, and last year I decided to experiment with growing some of the near-hardy terrestrial orchids known as Pleione. After flowering some last year in the spring, I grew them on over the summer and have now produced a new set of flowers.

Pleione orchids grow in the Himalaya, much of China and Taiwan, usually at high elevations where they are exposed to low temperatures in the winter and high rainfall much of the year. The habitat is mostly deciduous woodland, with the plants growing in the thick carpet of moss and leaf litter on the forest floor.

Unlike the more familiar large orchids from the tropics familiar in garden centres, they have an annual life cycle similar to many deciduous plants. In all but a few species the growth cycle starts in spring with the plant throwing up a single, very large flower on a stalk a few centimetres tall, followed by a single, large leaf. A few species differ in producing two leaves or flowering late in the year.
Flowers in Pleione are most often shades of lilac and white, with some producing pure white flowers and a few even yellow. There are often markings on the lip, the central petal of the flower, in darker shades, or red. These act as nectar guides to the pollinators, almost certainly specific species of bumblebee. The seed pod matures over the summer and then opens to release thousands of the typical dust-like seeds of orchids, which are dispersed by wind.

Orchid seeds are unusual in that they contain practically no food reserves for the young plant. Instead, orchids enter into a symbiotic relationship with fungi, and the fungi supply nutrients to the developing young plant. After a few years the storage organ, called a pseudobulb, which is the perennial organ in this species is large enough to support flowering and the life cycle continues.

As well as propagation by seed, Pleione also multiply vegetatively. When conditions and nutrients are in good supply, a flowering pseudobulb may produce two or more successor bulbs for the following year. They may also produce multiple much smaller bulbils at the apex of the pseudobulb which can be dispersed by rain washing over the colony and grow to flowering size more quickly than seed does.

In cultivation, Pleiones are quite easy to grow in most cases. They need a free draining compost and feeding during the growing season, and once the leaves die down in the autumn they should be kept cold and dry until January, when they can be repotted. In the summer they need to be kept in shady conditions. A few species will even grow outside in the UK, but to best see the flowers they are probably better grown in pots or pans.

P.Volcanello "Honey Buzzard"
As with many orchids, a great range of hybrids within the genus has been produced in cultivation. The products of a cross between the same two plants is called a grex. Parents of a grex may be two wild species, or one or both may themselves be hybrids. Since a single cross may potentially produce thousands of plants, each slightly different, a selected form may be given a varietal name. For example, the flower shown above is Pleine Volcanello “Honey Buzzard”, where Volcanello is the name of the grex and Honey Buzzard is the cultivar name. How complicated the parentage of orchi varieties can be is hown by the family tree of this plant:

Pleione Volcanello is a cross between the wild species P.bulbocodioides and the cultivar P. Soufriere
P. bulbocodiodes
P.Soufriere is a cross between P. Versailles and the wild hybrid P x confusa
P. albiflora
P x confusa is a cross between P.albiflora and P. forrestii (the yellow flower above)
P x Versailles is a cross between P.formosana and P.limprichtii

P.formosana alba
The plant flowering on my windowsill therefore carries genes from no less than five wild species, and as hybridization continues future cultivars will contain even more.

As with many orchids, in the wild Pleione species, especially those with limited range, may be threatened by collection from the wild, deforestation, or climate change. Currently one species, P.forestii, is listed as Endangered, and two others as Vulnerable. 

(Images from wikimedia. P formosana, limprichtii and P. Volcanello are my photos)

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