Stachyuraceae, a family of shrubs distributed from the Himalayas through China to northern Indochina and Japan, comprises a single genus, Stachyurus. Stachyurus praecox was discovered by the German explorer and physician Philipp von Siebold in Japan, and formally described by him, in collaboration with another German physician, Joseph Zuccarini, in their Flora Japonica (1836). As East Asia was gradually explored during the nineteenth and twentieth centuries, additional Stachyurus species were discovered. Today, Stachyurus comprises about eight species, half of which are endemic to China.
The taxonomic position of Stachyurus has been enigmatic since it was first described. In 1882, when only two Stachyurus species had been discovered, Joseph Hooker, Director of the Royal Botanic Garden Kew, claimed 'the most remarkable character in both species is that which misled botanists as to the affinity of the genus'; he appeared unconvinced by claims Stachyurus could be contained within the Theaceae. Towards the end of the century a separate family was created to accommodate the problem of Stachyurus. However, the relationships of Stachyuraceae remained a source of academic controversy during the twentieth century; suggested relatives included the Actinidiaceae, Hamamelidaceae and Violaceae. In the early twenty first century, analyses of multiple regions of chloroplast DNA revealed an unexpected relationship among the families Stachyuraceae, Crossosomataceae and Staphyleaceae. This group was formally recognised as the order Crossosomatales, and is where the Stachyuraceae currently rests.
Stachyurus praecox is a deciduous, endemic pioneer shrub, common along forest edges in warm temperate Japan. The species' scientific name reflects some of its biological characteristics; Stachyurus (literally 'tail-like spike') is a reference to the catkin-like inflorescence, whilst praecox ('early') is a reference to the shrub's very early flowering. The yellow, cup-shaped flowers mature on bare stems in early spring. In natural populations, the flowers of individual shrubs are either hermaphrodite or female. Field-based studies have shown individuals with hermaphrodite flowers mainly produce pollen and behave as if they are male, whilst individuals with female flowers produce fruit and are female. That is, Stachyurus praecox has functionally separate male and female plants (i.e., dioecious). In its native range, the primary pollinators are probably hover flies and solitary bees that are active early in the season.
Horticultural plants that flower early in the year are at a premium in European and American gardens. Hence it is unsurprising Stachyurus praecox found its way into British gardens fewer than thirty years after its initial discovery.
Further reading
Hooker JD 1882. Stachyurus praecox. Curtis's Botanical Magazine 108, t.6631.
Soltis DE et al. 2005. Phylogeny and evolution of angiosperms. Sinauer Associates, pp. 203-204.
Tetsuto ABE 2007. Sex expression and reproductive biology of Stachyurus praecox (Stachyuraceae). Bulletin of the Forestry and Forest Products Research Institute 6, 151-156.
Stephen Harris