This mountain ash is one of the smallest and most attractive of the white berry rowans. The seeds develop without pollination and the seedlings are identical clones of the mother. It seems to grow to a maximum of 2 metres in about twenty years.
The twigs are chocolate brown and the egg-shaped buds almost black. The compound leaves have on average 9-13 pairs of leaflets. The inflorescence is a loose white corymb. The white berries are quite large, about the same size as the mountain ash Sorbus aucuparia, with a touch of pink where the calyxes were.
Joseph Rock was an Austrian emigrant to the United States and a versatile naturalist; he collected this species in the Gansun province of China. It has been grown in continental Europe and Scandinavia since 1924, and is still usually called – mistakenly – S. koehneana; the true S. koehneana grows to five metres but is not grown in Europe at all, practically speaking.