A densely-branched shrub to 2 m tall. Shoots often reddish, glabrous or minutely hairy. Leaves ovate or elliptic, 0.5–17 × 0.5–3.8 cm, base rounded to cuneate, tip acute to caudate; glabrescent above and hairy especially under the vein axils; margin coarsely serrate, wavy, and often purple-tinged; petiole 1–3 mm. Inflorescence in April–June, a terminal pair of flowers on a peduncule 0.5–5 mm long. Calyx of 5 spreading reddish sepals 5–12 mm long. Corolla 1.1–2.8 cm long, white, red, sometimes yellowish or pink, lower part of tube narrowly tubular (1–2 mm wide), gradually becoming bell-shaped towards the mouth; bearded and with strong orange markings; upper lip 2-lobed, lower lip 3-lobed. Stamens nearly as long as the corolla tube; filaments sparsely hairy towards the base; ovary slender, 5–10 × 1 mm, longitudinally ribbed. Style 1.3–2 cm, sometimes slightly exserted, sparsely hairy. Fruit ripening September-November, linear, long-pointed. (Landrein & Farjon 2020).
Distribution Japan Honshu, Kyushu, Shikoku South Korea South Gyeongsang
Habitat On rocky sometimes limestone soils in hills and mountains, in woods and open places.
USDA Hardiness Zone 6
RHS Hardiness Rating H6
Conservation status Least concern (LC)
Like Diabelia serrata, this is a common and variable shrub in the southern half of Japan, which has also been collected (once) from the far south of South Korea. In addition to the common var. spathulata Landrein, Landrein and Farjon recognise var. colorata (H. Hara & S. Kuros.) Landrein, with pink to dark pink flowers, and var. miyagii Landrein, with entire leaves and often white flowers (Landrein & Farjon 2020). A plant of var spathulata with some double flowers (but not exclusively) was collected by T. Matsuzawa in 1991 and named f. duplexa Ohba (Landrein & Farjon 2020), while M. Yokoi and Y. Hirose (Yokoi & Hirose 1978) mentioned a Japanese garden form with white-mottled leaves.
The species was introduced to the UK by Charles Maries in 1880 and proved hardy, growing well at Leonardslee in West Sussex (Bean 1976) and forming a bush 2 m tall at the Sir Harold Hillier Gardens (Dirr 2009). Given the current nomenclatural instability, it is unclear whether any forms remain in cultivation in the west.