Sorbus alnifolia (syn. Aria alnifolia), also called alder-leafed whitebeam, Korean whitebeam, or Korean mountain ash,Chinese: 水榆花楸; pinyin: shui yu hua qiu; literally: "water elm rowan", is a species of whitebeam native to eastern Asia in eastern and northern China, Taiwan, Korea and Japan.
Sorbus alnifolia is a medium-sized deciduous tree growing to 10–20 m tall with a trunk up to 30 cm diameter and grey bark; the crown is columnar or conic in young trees, becoming rounded with age, with branches angled upwards, and slender shoots. The leaves are green above, and thinly hairy with white hairs beneath, 5–10 cm long and 3–6 cm broad, simple, usually unlobed (but see varieties, below), broadest near the base, with serrated margins and an acute apex. The autumn colour is orange-pink to red. The flowers are 10–18 mm diameter, with five white petals and 20 yellowish-white stamens; they are produced in corymbs 4–8 cm diameter in late spring. The fruit is a globose pome 8–15 mm diameter, bright red, with a dimple at the apex; they are mature in mid autumn.
There are three varieties:
- Sorbus alnifolia var. alnifolia. Leaves unlobed. Throughout the range of the species.
- Sorbus alnifolia var. angulata S.B.Liang. Leaves weakly lobed; fruit oblong. Northeast China, Korea.
- Sorbus alnifolia var. lobulata Rehder. Leaves weakly lobed; fruit globose. Shandong Province.
It has sometimes been placed in a separate genus of its own as Micromeles alnifolia, differing from other whitebeams in the deciduous sepals on the fruit (persistent in other whitebeams), but genetic evidence places it close to Sorbus aria.