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This species, widely distributed in the Himalaya and the Far East, is closely related to the common spindle-tree, differing in having the anthers purplish or reddish purple instead of yellow. It is a deciduous or semi-evergreen shrub or a small tree up to 30 ft high. Leaves variable, in size, shape, and relative width, broadest at or slightly below the middle, but sometimes oblanceolate to obovate, 21⁄2 to 6 in. long, 3⁄4 to 21⁄2 in. or slightly more wide, shortly toothed, glabrous on both sides or downy on the veins beneath. Capsules pink, four-lobed; aril orange to blood-red, sometimes split and exposing the seed.
E. hamiltonianus is a taxonomically difficult group, in need of detailed study. It does not subdivide neatly, but plants from the north-eastern corner of its range are distinct in their slender leaves (see var. maackii). Plants from Japan, S. Korea, and Sakhalin have been separated from E. hamiltonianus as E. sieboldianus, but all the characters given by Rehder to distinguish this species can be found in Himalayan plants. Komarov placed E. sieboldianus under E. hamiltonianus as a variety and gave as the difference that in var. sieboldianus the flowers are heterostylous: those with long styles have stamens with short filaments and vice versa, whereas in typical E. hamiltonianus the tendency is for flowers with long styles to have long filaments and vice versa (C. Jeffrey, Bot. Mag., n.s., t. 548). It is possible that there are also statistical differences in size and shape of leaves and fruits, etc. The Japanese plants, like those of China and the Himalaya, are variable, and Koehne’s three “species” – E. yedoensis, E. semiexsertus, and E. hians – represent slightly differing forms and were described from cultivated plants. See further below, under var. sieboldianus.
Typical E. hamiltonianus is represented in cultivation by plants known by the synonymous name E. lanceifolius; these were probably all raised from Wilson’s No. 1105, collected in W.China during his expedition for the Arnold Arboretum. They are semi-evergreen, vigorous large shrubs or small trees up to 30 ft high, but do not fruit freely. Wilson also sent seeds from W. China when collecting for Veitch (W. 1202), and the material figured in Bot. Mag., n.s., t. 181, came from a plant at Kew raised from this number.
var. sieboldianus – This is given the rank of a subspecies of E. hamiltonianus by Dr Hara, distinguished by its larger fruits 7 to 10 mm long and 7 to 13 mm wide, shallowly depressed in the centre, against 5 to 8 mm by 7 to 10 mm in the typical state of the species, and the larger seeds.
The status of Chinese members of the complex is uncertain. But the Wilson introductions from Hupeh and western Szechwan, identified as E. lanceifolius in Plantae Wilsonianae, belong almost certainly to var. sieboldianus. As for E. lanceifolius itself, described by Loesener from a specimen collected by Henry in south-east Yunnan, this is certainly not a distinct species. It belongs to E. hamiltonianus sens. lat., and agrees with var. sieboldianus in having larger fruits than in typical E. hamiltonianus. Relative width of leaf is not in itself of any significance in this complex, since narrow-leaved forms occur throughout the range of the species, including Japan.
E. maackii Rupr.
E. europaea var. maackii (Rupr.) Reg
E. sieboldianus Bl.
E. hamiltonianus subsp. sieboldianus (Bl.) Hara
E. yedoensis Koehne
E. hians Koehne
E. semiexsertus Koehne
E. nikoensis Nakai
varieties based by Blakelock on the preceding four species
E. vidalii Fr. & Sav