Evergreen Tree
Distylium, Genus, racemosum, Species,
- Genus & species
Isu tree
Southern Japan, Ryukyu Islands, and adjacent East Asia
Overview
Distylium racemosum is a dense, broadleaf evergreen tree that grows 15–30 feet (4.6–9 m) tall and 10–20 feet (3–6 m) wide in cultivation, and 50–80 feet (15–24 m) tall in native forests, with a rounded crown and many densely twigged branches. Leaves are alternate, elliptic to obovate, 2–4 inches (5–10 cm) long, leathery, glossy dark green, with entire margins and a short petiole. Flowers are small, without petals, in short racemes 1–2 inches (2.5–5 cm) long, with red stamens and anthers, in early spring. Fruits are woody, hairy capsules 0.4–0.5 inch (10–13 mm) long that split to release shiny black seeds. Aphids form rounded galls 0.5–1 inch (1.3–2.5 cm) across on leaves and twigs, which are left empty after the insects leave. Hardiness is USDA zones 7–10. Growth is slow to moderate, adding 6–12 inches (15–30 cm) per year. The wood is dense and hard.
Native Range
Distylium racemosum is native to southern Japan, the Ryukyu Islands, and adjacent parts of East Asia, where it grows in evergreen broadleaf forests and coastal woodland. It is common along the Pacific coast of Japan from Honshu southward.Suggested Uses
Distylium racemosum is used as a clipped hedge, windbreak, and screen in coastal and mild-winter regions, with spacing of 3–5 feet (0.9–1.5 m) between hedge plants. It is also planted as a specimen and street tree in Japan, and the wood is used for combs, tool handles, and instruments.How to Identify
Appearance
Size & Dimensions
Height15' - 30'
Width/Spread10' - 20'
Bloom Information
Distylium racemosum blooms in early spring, typically March to April, with racemes lasting 2–3 weeks. Flowers have no petals, and red stamens supply the visible color. Wind and insects carry pollen, and capsules ripen in autumn.
Detailed Descriptions
Flower Description
Red stamens, no petalsFoliage Description
Glossy dark greenGrowing Conditions
Sun Requirements
Requires 4-10 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Distylium racemosum grows in full sun to part shade, with 4–8 hours of direct light, in moist, well-drained soil of pH 5.5–7.0. Plants tolerate clay, sand, salt spray, and short dry periods once established. Hardiness is USDA zones 7–10, with leaf damage below 15°F (−9°C). Young plants need 1 inch (2.5 cm) of water weekly in the first 2 years. A 2–3 inch (5–8 cm) mulch layer limits root drying. Aphid galls, scale insects, and sooty mold occur occasionally.Pruning
Pruning takes place in late spring after new growth hardens, shearing hedges to the desired height and shaping individual plants. Plants regrow from old wood after cutting to 12–18 inches (30–45 cm). Dead and crossing branches are removed in late winter.Pruning Schedule
Prune: May–June
late spring
