Iroha-momiji: leaves, winged fruits and cultivars

Iroha-momiji is a deciduous Japanese maple generally listed as Acer palmatum, the name also associated with Chinese jizhuaqi. In narrower treatments it corresponds to A. palmatum subsp. palmatum. Kew recognises two further subspecies, amoenum and matsumurae. “Japanese maple” is a wider horticultural expression and can also refer to related species.

A leaf is deeply divided into five to seven pointed lobes, with uneven double teeth along the margins. These are connected parts of one simple leaf, rather than separate leaflets. Leaves grow in opposite pairs on a twig. A familiar explanation of iroha-momiji links the name to counting the lobes with the first seven syllables of the iroha sequence.

The tree flowers as well as producing colourful leaves. Japanese botanical accounts place its small dark-red flowers around April and May. They are followed by paired samaras, each fruit bearing a thin wing. The Kyushu branch of Japan’s Forestry and Forest Products Research Institute records ripening in September and October; young winged fruits can be visible well before then.

Winged fruits descend while rotating and can be dispersed by wind. A species account published by the Japanese Society of Revegetation Technology uses that spinning descent to explain wind dispersal. Germination is a separate stage: seeds are already dormant when they leave the parent plant, and moist, cold conditions can help break that dormancy. A fallen samara is therefore not evidence that a seedling will emerge immediately.

In Japan, wild iroha-momiji occurs in warmer parts of Honshu, Shikoku and Kyushu, including woodland and waterside settings. Its planted range is much wider. Kew currently gives A. palmatum a native range in southwestern Korea and central and southern Japan. Broader accounts that include China and other regions do not necessarily delimit the taxon in the same way.

As autumn advances, green chlorophyll breaks down and red anthocyanin pigments are produced. Timing varies with location and year. Tokyo’s Institute for Nature Study reported many iroha-momiji areas at their best on 11 December 2024—a dated local observation, rather than a calendar for the whole country.

Chiba City’s comparison separates the smaller, usually five- to seven-lobed iroha-momiji from yama-momiji, usually with seven to nine lobes. Both have double teeth, while ō-momiji has finer, single teeth. Size ranges overlap. Fruit form and leaf margins add useful evidence, while the botanical rank used for these relatives depends on the classification.

Cultivars offer different combinations of leaf colour, depth of division and growth habit. Some have finely cut foliage; others form weeping crowns. A horticultural cultivar is a selected form maintained for particular traits, whereas a subspecies is a botanical category. The two names answer different questions.

Japan’s National Museum of Nature and Science names Seigen (清玄) as a small cultivar suited to bonsai. The Royal Horticultural Society describes its rounded, multibranched habit and small, usually five-lobed leaves: bright red when young, light green in summer, then orange and gold in autumn. The example combines growth habit with seasonal colour. Red young leaves should not be mistaken for autumn colouring, and a cultivar name does not designate a new wild subspecies.

Grafting helps retain a selected cultivar. A shoot from the chosen plant is joined to a rootstock so that the two grow together; seedlings may not reproduce the parent cultivar’s traits. The Royal Horticultural Society lists A. palmatum among commonly grafted ornamentals and also describes propagation by softwood cuttings. Wild trees and all cultivated trees should not be assumed to have the same propagation history.

Grafting joins living tissues. The cambium is a dividing layer between the wood and phloem; the scion’s cambium must meet the rootstock’s. Tokyo University of Agriculture explains the general process for cut grafts in woody plants: wound tissue forms and fuses, then connecting cambium and vascular tissues develop, allowing water and nutrients to pass between the parts. The scion retains its cultivar traits while the rootstock supplies the roots. The joined plant is not a seed-grown offspring of the two trees.

Edo horticultural books recorded and circulated distinctions in maple foliage. Chiba University holds three manuscript collections by Itō Ihei Masatake, covering 36, 36 and 28 forms, with coloured leaf illustrations, descriptions and associated waka poems. Its catalogue dates Koka-sen kaedeshū to 1710; the surviving manuscript’s individual leaves are not independently dated by that catalogue year.

Nagai Botanical Garden identifies the late Edo and early Meiji periods as active times for cultivar development, while warning that a historic and a modern plant with the same name may not represent an identical line. Modern living collections combine preservation with production. The Japan Nurserymen’s Association’s maple programme seeks to collect native maples and historic cultivars and exchange material internationally; its stated collection goals cover maples broadly.

Iroha-momiji is used in gardens, parks and bonsai, and can form shaded walks such as the named avenue at Koishikawa Botanical Gardens. Moisture and drainage matter in cultivation. The Royal Horticultural Society notes that insufficient soil moisture or excessive exposure may cause leaf scorch. Cultivar and growing conditions therefore influence how a garden tree looks through the seasons.