Mahonia oiwakensis

This species has long been known by the name Mahonia lomariifolia, published by Takeda in 1917.[6] Under that name, it was considered to occur only in mainland China, while on Taiwan, a second species was found, known as M. oiwakensis. Modern taxonomic sources unite the two as a single species,[2] but as the latter name was published a year earlier by Hayata,[7] it has priority and is thus the accepted name. In recognition of the morphological differences between the Taiwanese and mainland Chinese plants, Shaw[8] recognized the two as subspecies of Mahonia oiwakensis: M. oiwakensis subsp. oiwakensis in Taiwan and M. oiwakensis subsp. lomariifolia in mainland China. In addition, a plant collected in Yunnan with especially narrow leaflets was described as a new variety: Mahonia oiwakensis subsp. lomariifolia var. tenuifoliola.[8]

Mahonia oiwakensis is a shrub or tree up to 7 m tall. Leaves are up to 45 cm long, compound with 12-20 pairs of leaflets plus a larger terminal one, dark green above, yellow-green below. The inflorescence is a fascicled raceme up to 25 cm long. The berries are egg-shaped, dark blue, sometimes almost black, up to 8 mm long.[2][7]

Mahonia oiwakensis subsp. lomariifolia is one parent of the important garden hybrid Mahonia x media, which includes popular cultivars such as 'Charity', 'Winter Sun' and 'Lionel Fortescue' (the other parent is Mahonia japonica).[9] It is also a parent of the cultivar 'Arthur Menzies', though with Mahonia bealei as the other parent.[10] In the wild in Taiwan, M. oiwakensis subsp. oiwakensis appears to hybridize with wild Mahonia japonica.[8]

Mahonia oiwakensis subsp. lomariifolia has gained the Royal Horticultural Society’s Award of Garden Merit.[11][12]