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This was mentioned under B. caerulea-grandis (wrongly spelt with the once customary ‘oe’ in place of the more correct ‘ae’ actually used by Blanchard). It was thought to be a hybrid, with B. populifolia as one parent, B. caerulea-grandis or B. papyrifera as the other. Recent research has shown that the parentage is in fact B. populifolia × B. cordifolia (B. papyrifera var. cordifolia) and that B. caerulea-grandis, far from being a species, is itself a hybrid of the same parentage (Canad. Field-Nat., Vol. 81, pp. 116–217 (1967) and Canad. Journ. Bot., Vol. 48, pp. 2241–7 (1970)). Blanchard’s two names were published simultaneously, but clearly the name B. × caerulea is the one that should be used, since he himself reduced B. caerulea-grandis to varietal rank as B. caerulea var. grandis later in the same year.
specimens: (grown as B. caerulea-grandis): Alice Holt, Hants, pl. 1962, 50 × 2 ft (1980); University Botanic Garden, Cambridge, pl. 1925, 46 × 21⁄2 ft (1982); Westonbirt, Glos., pl. 1934, 58 × 21⁄2 ft (1981); Hergest Croft, Heref., 70 × 71⁄4 ft (1985).×