Where it can be found in cultivation or the wild, the fragrant epaulette tree is often prized for its year-round beauty. Its most acclaimed features are the beautiful pendant clusters of white flowers in the spring. The autumn-occurring hanging fruits undoubtedly sustain the tree’s elegance once the flowers have gone.
Online resources on the name of this species seem to vacillate between Pterostyrax hispidus and Pterostyrax hispida (the difference being in gender designation). The species is correctly named using the masculine suffix (-us). Native to Japan, it grows on forested sites in mountainous environments. A valued trait of the epaulette tree is the spread of the branches that nearly equals the height of the tree, providing a large area of shade. Trees can grow to 15m (50 ft.), but in cultivation or urban settings may take the form of a tall shrub (reaching ~6m (20 ft.)). According to the USDA’s hardiness zones, cold hardiness ranges from 5a to 8a, enough for it to be suitably planted throughout much of the warmer temperate world. Although it hasn’t historically been very common in cultivation, in 1993 it was awarded the Royal Horticulture Society’s Award of Garden Merit.
Fragrant epaulette, if not in the context of this tree, would imply an aromatic shoulder piece typical of military uniforms. Here however, it refers to the fragrant flowers (PDF, with photo) hanging to one side, significantly resembling these decorative symbols of many higher-ranked military officers. The small, bristled fruits that shine in the sun are described by the specific epithet, hispidus (bristly-hairy). These clusters of dry drupes tend to persist on the branches once the leaves have dropped for winter. It took me a few days of different sunlight and quite a few pictures to finally get a photo that I thought nicely reflected the charm of the fragrant epaulette tree. I’ll certainly keep an eye on it in the spring as the flowers come into bloom.
Pterostyrax is comprised of only four species, each native to east Asia and all quite similar in morphology. Styrax is a related genus in the storax family which includes numerous attractive garden plants, many of which can be found in UBC’s David C. Lam Asian Garden. One easy way to distinguish the two genera lies in the slightly winged fruits of Pterostyrax, hence the prefix “ptero”. When flowering in the spring, this family of plants can be a highlight in suitable gardens. As an aside, the genus Styrax contains around 130 species while no other genus in the family contains more than five species.
Studies on an oligophagous ladybird beetle in Japan looked at four different host tree species, including Pterostyrax hispidus. Significantly higher survivorship was found in larvae occupying Pterostyrax hispidus, even though it was deemed to be a lower quality food-host. These populations ultimately benefited from the epaulette tree’s abundant leaves and their persistence through a long growing season.