Alnus cremastogyne Burkill

Along with Alnus lanata and A. ferdinandi-coburgii, A. cremastogyne belongs to Section Cremastogyne, a distinct group characterized by single female flowers, fruit held in the leaf axils, leaves all broadest at the apex and coming to an abrupt acute tip, and distinct black scaly buds. Of these three species A. cremastogyne is readily distinguished with its more or less glabrous leaves and twigs, and by its soft, resinous fruit borne on long pendulous peduncles. A. lanata by contrast is densely white-buff hairy, especially on young shoots and leaf undersides. A. ferdinandi-coburgii has erect fruit borne on very short peduncles and is also more or less glabrous. The ranges of these species overlap, and it is possible they may hybridise, with all recorded as being tetraploid except A. cremastogyne (tetraploid and diploid). Although the general consensus is that these three species are distinct, further inventigation is warranted.

This is a highly adaptable alder, with a short juvenile period, high seed yield, and rapid growth rate. This is represented in its genetic diversity and wide geographical range (Guo et al. 2019). It is grown in quantity in its native range and makes a fast-growing tree, valued for firewood, timber, for soil stabilisation and agroforestry, and as a green manure (Li 2001; Wang 1986). It primarily grows in temperate regions, in habitats with ample sunlight and summer heat. In cultivation in cool-temperate regions it is susceptible to damage by early and late frosts, but in regions with mild winters and summer heat it grows quickly into a tall straight tree. In all cases it grows best in damp conditions protected from cold winds, and in optimal sites is occasionally semi-evergreen.

Alnus cremastogyne was discovered by Augustine Henry in Sichuan in 1899 and introduced by Ernest Wilson in 1907. Material traceable to Wilson’s introduction has probably died out, but it continues to be represented by several subsequent introductions. Nevertheless it remains a rare tree in cultivation outside its native range, with plants known only from major collections such as Kew, Ness and a few others in the UK. The plants at Kew and Ness were raised from seeds received from the Chinese Academy of Forestry in 1976 or 1977, while others are traceable to collections made on the SBEC expedition of 1980, in Sichuan. These collections have so far made straight single-stemmed trees to 7–10 m tall. There is a question as to the hardiness of A. cremastogyne in cultivation, often showing cold damage to early flushes of foliage and inflorescences, but the tallest examples in cultivation are younger than those mentioned above, suggesting provenance has an important bearing on performance: trees at Howick from H&M 2102 were 18.5 m in 2019; one planted at Tregrehan in 1989 was 18 m in 2014; and in Ray Wood at Castle Howard, North Yorkshire, a tree planted in 1990 has made a beautiful straight-stemmed specimen 17.6 m in 2019 (The Tree Register 2021). A. cremastogyne is susceptible to Alder Leaf Beetle and is frequently badly damaged or defoliated (T. Baxter pers. obs.).