Tuesday, 25 November 2014

The origin of the ‘King of Flowers’.


The Domestic Tree Peony, Paeonia suffruticosa, has a long history of cultivation in China, where records of the plant growing in gardens go back at least 1400 years. Domestic Tree Peonies are noted for their beauty and fragrance, and are known as the ‘King of Flowers’ in China. However the precise origin of the domestic Tree Peony is obscure, with most experts believing that it is a hybrid of two or more of the wild Tree Peony species found in China, but with no consensus as to which plants might be involved.

In a paper published in the Proceedings of the Royal Society: SeriesB, Biological Sciences on 5 November 2014, a team of scientists led by Shi-Liang Zhou of the State Key Laboratory of Systematic and Evolutionary Botany at the Institute of Botany at The Chinese Academy of Sciences describe the results of a genetic study of Paeonia suffruticosa and the nine wild Tree Peony species found in China, in order to determine the relationships of the domestic plant.

The ‘King of Flowers’, Paeonia suffruticosa, at Prague Botanic Garden. Karel Jakubec/Wikimedia Commons.

Zhou et al. found that Paeonia suffruticosais a hybrid of at least five wild species, Paeonia cathayana, Paeonia rockii, Paeonia qiui, Paeonia ostii and Paeonia jishanensis, with most of the cultivars obtained by hybridizing female Paeonia cathayana flowers with males of another species, though sometimes other plants had been used as the female, and many cultivars had been achieved by further hybridization.

Zhou et al. further note that all the wild Tree Peony species involved come from central China, the area in which the domestic plant was first cultivated, and that the majority are now rare or endangered. In particular they note that only a single specimen of Paeonia cathayana, the species that appeared to contribute the most to the origin of the domestic plant, could be found growing in the wild, in the mountains to the south of Louyang. Paeonia ostii also seemed to be reduced to a single wild specimen, this time on a cliff in central Anhui Province, and Paeonia qiui was found only in a handful of small populations in western Hubei Province. Paeonia jishanensis still has several relatively large populations, but this species is known to reproduce vegitatively (non-sexually), so it is unclear how genetically diverse these populations are (low genetic diversity populations can be extremely vulnerable to disease, and apparently large and healthy populations are sometimes wiped out suddenly). Only one species, Paeonia rockii, is still relatively widespread, being found across a large area of central and western China, but this is widespread population is largely composed of widely scattered very small populations and individuals, making this species also vulnerable.

The distribution of nine wild tree peony species. (1) Paeonia ludlowii; (2) Paeonia delavayi; (3) Paeonia decomposita; (4) Paeonia rotundiloba; circle, Paeonia rockii; diamond, Paeonia jishanensis; square, Paeonia ostii; triangle, Paeonia qiui; hexagon, Paeonia cathayana. Zhou et al. (2014).

Approximately one tenth of the dry land surface of the Earth has now been converted to agricultural purposes by Humans, and that while this has benefitted us enormously, it has come at great cost to many wild species, particularly the progenitors (wild ancestors) of most of our crops, which for the most part formerly grew in the best areas for growing their domestic relatives. This is known to present food security problems for Human populations, as domestic crops tend to be less genetically diverse and therefore more vulnerable to disease than their wild relatives, and the loss of these wild relatives reduces the available genetic diversity that might be needed to breed crops resilient to as yet unknown threats. Zhou et al. observe that in addition to this known problem with agricultural plants, the widespread cultivation of ornamental plants in parks and gardens presents an additional threat to biodiversity, that should also be a focus for botanists and conservationists.

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