Pterostyrax psilophyllus Diels ex Perkins

Pterostyrax psilophyllus is the rarest of the three Pterostyrax in cultivation, but is grown in collections throughout our area and is commercially available in North America, where Jacobson (1996) records an introduction in 1983 and a release to the market by Piroche Plants in about 1993. Its inflorescences are intermediate in length between those of P. corymbosus and P. hispidus, and appear consistently earlier than those of the latter (Clarke 1988). A 6 m, single-stemmed specimen seen at the Morris Arboretum in late May 2006 had finished flowering, while a tree of P. hispidus nearby was in full flower. At Quarryhill, a tree grown from SICH 0845, planted in 1993, was 8 m tall in 2004. This had also formed a single stem, and had greyish brown bark. Another collection was made on the Sichuan Expedition of 1999, under the number SICH 2012, from trees reaching 15 m in regenerating broadleaved woodland, and a specimen from this material grows at Kew. The species has also been collected in Hubei (by the 1994 NACPEC expedition, for example, under 96750), giving rise to specimens in several American collections. The earliest introductions, as recorded by Clarke (1988), however, came by the more prosaic route of the Index Seminum of Beijing Botanical Garden, seed from this source being received at Kew in 1963. The specimen at Wakehurst Place mentioned by Clarke (1988) is still alive, and had reached 7 m when measured in 1996 (Kew database). At Westonbirt there is a tree of c.10 m, derived from Shanghai Botanic Garden seed (S. Andrews, pers. comm. 2008).

In one of his last contributions to New Trees before his untimely death, Peter Wharton wrote from Vancouver (pers. comm. 2008): ‘We grow a number of collections of this species, notably two I made in 1994 in the Dashahe Cathaya Reserve, northern Guizhou under PW 6 and PW 59. In the wild this species has the capacity to become a large forest tree and is often a target for selective felling. Trees growing in the David C. Lam Asian Garden have been heavily damaged by voles gnawing at the lower trunks, severely reducing height growth. Two trees are now just over 4 m and appear to be growing away rapidly. We have also three trees derived from seed collected on Emei Shan by Shanghai Botanic Garden in 1992. These have proved to have immense vegetative vigour, growing to over 17 m, before being badly damaged by heavy snow in November 2006, when still in leaf. Although hardy here, Pterostyrax psilophyllus is weak-wooded, and the small terminal flowers are often hidden by heavy foliage.’