Article from Bean's Trees and Shrubs Hardy in the British Isles
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'Alloberberis trifoliolata' from the website Trees and Shrubs Online (treesandshrubsonline.
See the genus entry for Alloberberis for a brief discussion of the taxonomy of this species. The text below is heavily adapted from Bean to take account of the latest understanding of the systematics.
An erect, rigid shrub 6 or 8 ft high, with only three leaflets to each leaf. Leaflets lustrous green, glaucous or almost white, shaped like a spear-head, 1 to 2 in. long, 1⁄4 to 3⁄5 in. wide, tapering to a long, spine-tipped point, and bulging at each side into one or two spine-tipped lobes. Flowers yellow, borne in short corymbs. Fruits oval or roundish, black with a blue bloom.
This rare shrub ranges from W. Texas to N. Mexico, and is only hardy against a sunny wall, or in exceptionally mild districts. There was once an old bush, 8 ft high, growing against the house wall at Bayfordbury in Herts.This variety differs from all the other cultivated mahonias in the glaucous-white leaves with only three leaflets. It was introduced to Britain in 1839 by Hartweg, who collected the seeds in Mexico on the road from Zacatecas to San Luis Potosi.
Bean worked on the assumption that the glaucous- or almost white-leaved plants familiar from cultivation and frequently seen in the wild belonged to var. glauca (I.M.Johnst.) C.C.Yu & F.K.Chung, and that the green-leaved plants confined (so Bean said) to southern Texas represented the typical state. However, the Flora of North America (2025) does not recognise infraspecific taxa for this species, noting that ‘weakly and strongly glaucous plants are often found in the same population’. Accordingly, we reduce var. glauca to synonymy with the type.