Robinia × holdtii Beissn.

A hybrid between R. luxurians and R. pseudoacacia whose racemes are looser and longer than in R. luxurians and the flowers of a paler colour. The keel and wing-petals are almost white, the standard pale red with white markings. Habit and vigour of growth similar to those of R. pseudacacia. Pod rather glandular. Obtained by Mr Von Holdt, Alcott, Colorado, and put into commerce about 1902. The same hybrid was raised in Späth’s nurseries, Berlin (see ‘Britzensis’). The tree named R. coloradensis by Dode was one of six raised by Vilmorin at Les Barres from seeds collected by E. L. Berthoud at Golden, Colorado, probably from a tree of R. × holdtii. Another of the seedlings is described in Fruticetum Vilmorinianum (1904), p. 54, as ‘R. neomexicana var.?’.

Mr Bean’s statement that this hybrid grows as vigorously as R. pseudoacacia ought to have been amended: two specimens in the Kew collection, over eighty years planted, measure only 48 × 33⁄4 ft and 52 × 23⁄4 ft (1981). The cultivar ‘Britzensis’, however, planted at Borde Hill, Sussex, in the 1930s, has reached 62 × 41⁄4 ft (1984) (Clarke 1988).