Chinese wisteria
Wisteria sinensis is a woody climbing legume native to Central China. The long tresses of lilac flowers are unmistakable and have been a favourite of British gardeners since the early nineteenth century. Wisteria sinensis was first introduced to Britain in 1816 by John Reeves, Chief Inspector of Tea at Canton, as cuttings from a plant growing in the garden of a Chinese merchant in Canton. In Britain, the plants flowered as early as 1819 and cuttings were selling for about six guineas each. By 1835, wisterias were so common in Britain they were selling for less than two shillings per plant. Trained up walls and along pergolas, wisterias take time to reach their full magnificence.
The genus, comprising about six species, has a disjunct distribution between east Asia and North America, and is a so-called Tertiary relic. The generic name Wisteria commemorates the late eighteenth-century, North American anatomist Caspar Wistar. Unfortunately, when he named the genus, Thomas Nuttall misspelled Wistar's name. The international rules of botanical nomenclature mean Nuttall's orthographic error will be with us forever.
Two wisterias, Wisteria sinensis and the Japanese wisteria (Wisteria floribunda), have become popular in cultivation; the two species are readily distinguished. Wisteria sinensis has anticlockwise climbing stems, scentless flowers and few than 11 leaflets per leaf, whilst Wisteria floribunda has clockwise climbing stems, scented flowers and more than 12 leaflets per leaf. In their native habitats, these species are geographically isolated. However, once they meet each other in cultivation they may cross with each other to produce prolific hybrids. Individual plants, with woody stems up to 20 m long and more than 30 cm in diameter clambering over forests can become serious weeds. For example, over the last 40 years, hybrid wisterias have become a major concern in the southeastern United States.
In addition to their ornamental interest, wisterias are also of evolutionary interest. Besides nuclear DNA, plant cells also contain DNA in their organelles such as chloroplasts and mitochondria. These organelles, essential for photosynthesis and respiration, are inherited through the maternal line in most flowering plants, i.e., seeds get these organelles from their mothers. However, wisteria is unusual in that chloroplasts are inherited from a seed's father (pollen parent) and mitochondria are from a seed's mother (egg parent). Wisterias, and its close relatives, are also distinguished from the many thousands of other legumes since they have a major deletion in the chloroplast DNA.
Further reading
Hu Y et al. 2005. Potential cytoplasmic inheritance in Wisteria sinensis and Robinia pseudoacacia (Leguminosae). Plant Cell Physiology 46: 1029-1035.
Trusty JL et al. 2007. Identity of naturalised exotic Wisteria (Fabaceae) in the south-eastern United States. Weed Research 47: 479-487.
Stephen Harris