A group of some 60 species of deciduous trees and a few shrubs, all except three found in the temperate latitudes of the northern hemisphere. They have normally opposite, equally pinnate leaves, but in some species and varieties the leaflets are reduced to one, and the leaves are sometimes in whorls of three, and on odd shoots not infrequently alternate. The inflorescences vary considerably in beauty in different species. In the most ornamental group, the ‘flowering’ ashes, both corolla and calyx are present, and the flowers are borne very numerously in panicles from the end of the young shoot and from the axils of the terminal pair of leaves. This is the section Ornus (manna ash group). In F. chinensis and its Japanese ally the flowers are borne as in the manna ash, but they lack petals (section Ornus, subsection Ornaster). In the second and larger section of the genus – section Fraxinus (Fraxinaster) – the flowers are produced before the leaves from lateral leafless buds on the previous season’s shoots, and are without petals (except in the anomalous F. dipetala). In the subsection Bumelioides, to which our common ash (F. excelsior) belongs, the calyx, too, is lacking.
The flowers are sometimes perfect, sometimes unisexual; and perfect male and female flowers may be found either altogether or separately on one tree. It is said that the flowers of a tree may sometimes be all or mostly one sex one year, and the other sex the next. Stamens usually two. Fruit one- or two-celled, one- or two-seeded, developing at the end a long, flattened wing or membrane, usually from 3⁄4 to 11⁄2 in. long and 1⁄4 to 1⁄3 in. wide. Many of the species hereinafter described do not flower in this country, and even those that do, like the common ash, do not carry crops of fruit every year. From all its allies in gardens, except Jasminum and one species of Syringa, Fraxinus is distinguished by its pinnate leaves.
In gardens and parks, the ashes are welcome for their stately form and fine pinnate foliage. Some of them, like F. excelsior and F. americana, yield an admirable timber. They are frequently found in nature on a limestone formation, and should be especially noted by those whose ground is so situated. For the rest, they are gross feeders, and like a good soil and abundant moisture. They should always, if possible, be raised from seeds, which may be sown in cold frames or shallow boxes, and thinly covered with soil. Grafting for the weeping, coloured, and other garden varieties has, perforce, to be resorted to, but the stock should always be of the species to which the variety belongs. The ashes produce a very fibrous and extensive root system, which renders their transplanting safe and easy. The only species at all unsatisfactory in cultivation are those like F. nigra and F. mandshurica, which, being excited into growth by unseasonable warmth early in the year, are almost invariably cut back by later frost. Some species, like F. dipetala, need rather more warmth than our climate affords. But given a good soil, and not too exposed a position, the ashes generally are satisfactory.
The following is a selection of the more desirable species:
F. angustifolia; F. americana; F. excelsior diversifolia, ‘Jaspidea’ and ‘Pendula’; F. latifolia (oregona); F. mariesii; F. oxycarpa; F. pennsylvanica; F. ‘Raywood’; F. spaethiana; F. velutina.
The only important modem work on the ashes is Gertrude N. Miller’s study of the North American species (Cornell Univ. Agric. Exp. Stn. Mem. 334, February 1955).
From the Supplement (Vol. V)
The taxonomy and nomenclature of some east Asiatic species are clarified by Toshiyuki Nakaike in ‘A Synoptical Study on the Genus Fraxinus from Japan, Korea and Formosa’, in Bull. Nat. Sci. Mus. Tokyo, Vol. 15(3), pp. 475-512 (1972).
A valuable study of the cultivated species by H. Scheller appeared in the Mitteilungen of the German Dendrological Society (Mitt. Deutsch. Dendr. Ges.), No. 69, pp. 49-162 (1977).