In Bloom: ‘Inazuma’ Japanese Maple, The Thunderer

The striking foliage shapes lends to its uproar of a name.   Acer palmatum ‘Inazuma’, The Thunderer.  Photo: Aleks Monk.

The large upright Japanese maple just past the gatehouse, on the right side of the path, is Acer palmatum ‘Inazuma.’ This cultivar (cultivated variety) has been recorded in Japan since 1882, but here it’s still somewhat rare and difficult to find. Most sources translate its name as “the thunderer” or “the thunder,” but there are also references to Inazuma, a goddess of lightening in Japan’s original religion, Shinto, which saw gods in all of nature.

‘Inazuma’ is included in the Matsumurae Group, one of seven groups that are used to categorize Japanese maples. This system is useful for distinguishing among the hundreds of cultivars that have been developed, not only in Japan, but throughout the world, with new introductions occurring every year.

Five of these seven groups are based on how the leaf lobes are divided: broad lobes that are moderately divided, up to 2/3rd of the way to the leaf base (Amoenum Group); broad lobes even more deeply divided, like the fingers of a hand/palm (Palmatum Group); somewhat narrower lobes that are very deeply divided (Matsumurae Group); narrow, straplike lobes deeply divided to the leaf base (Linearilobum Group); narrow lobes very deeply divided and deeply dissected into sublobes (Dissectum Group). The final 2 groups are catchalls: dwarf cultivars – those with a mature height of about 6 feet or less (Dwarf Group); and cultivars that don’t fit into any of the first six groups (Other Group).

The size, shape and color of its foliage give ‘Inazuma’ a very striking appearance. Each large leaf consists of seven lobes that are long and “ovate-lanceolate” in shape (combining an egg-shape with that of a lance), with a short reddish petiole (leaf stalk). The lobes are deeply divided, almost to the leaf base, and have strongly toothed edges. Emerging spring leaves are deep red or purple-red in color — maturing in summer to a dark purple, tinged green, with green veins. In shady conditions, and in very hot weather, the summer color tends toward green, rather than purple. Fall color is vivid crimson.

‘Inazuma’ is a striking presence at the entry to the garden. Photo: Aleks Monk.

‘Inazuma’ is a very cold-hardy, strong growing tree, with a mature size (at 20-25 years) of about 30 feet tall by 20 feet or more in width. It develops a rounded canopy, and its branches and foliage have a somewhat cascading habit. It has also been known under the names of ‘Dissectum Inazuma’ and ‘Pendulum Inazuma,’ although these names are misleading and don’t accurately reflect the categories discussed above.

Like all Japanese maples, ‘Inazuma’ grows best in moist, fertile, well-drained soil, in full sun or part shade, and with regular watering during our dry summers. Best color develops when grown in full sun, which it tolerates well in our climate – as long as it’s not subjected to the stress of significant reflected heat.

‘Inazuma’ is a beloved maple in our Seattle Japanese Garden — a powerful presence as we walk through the entry gate and leave the everyday world behind.

Corinne Kennedy is a guide for Seattle Japanese Garden and a contributor to the garden’s blog.