Under this name it is convenient to group the so-called ‘French’ hybrids, which arose from the crossing of two deciduous species – the tender, blue-flowered C. coeruleus of Mexico (introduced to Europe in 1818) and the hardy, white-flowered C. americanus. In 1838, Loudon had suggested that this cross would be ‘a very desirable acquisition’, unaware that it had in fact been made some years earlier in France – the result being C. ‘Delilianus’ (syn. C. arnouldii). Following Rehder, we take this as the typical form of the hybrid group C. × delilianus, to which many beautiful additions were made, all by French breeders, during the ensuing decades of the nineteenth century.
C. × pallidus Lindl. – The ceanothus so named by Lindley is thought to be the result of crossing C. ovatus (a white-flowered species closely allied to C. americanus) with ‘Delilianus’. Some of the ‘French hybrids’, in particular those with rose-coloured flowers such as ‘Marie Simon’, may be the result of similar crosses (though a paler flower colour, due to the dilution of the C. coeruleus blood, might also be expected from back-crosses within the C. × delilianus group).
However, from the horticultural viewpoint the distinction between the C. × delilianus and C. × pallidus is really of little moment. Together they form a most useful race of summer-flowering shrubs; all are deciduous and bear their flowers in panicles on the new wood. They must be hard pruned each spring in March or April, cutting back nearly to the base of the previous year’s wood. The following is a selection:
‘Ceres’. – Lilac-pink flowers in large panicles.
‘Delilianus’. – Flowers sky-blue.
‘Gloire de Plantières’. – Dwarf-growing, deep blue flowers.
‘Gloire de Versailles’. – Large panicles of powder-blue flowers. Perhaps the most widely cultivated of the group.
‘Henri Desfosse’. – Similar to ‘Gloire de Versailles’ but with deep blue flowers.
‘Indigo’. – The deepest blue of these hybrids but tender in some districts.
‘Leon Simon’. – Light blue flowers in clusters.
‘Marie Simon’. – Rose-pink flowers. A pretty variety.
‘Perle Rose’. – Bright carmine-rose flowers, but the colour is variable on some soils.
‘Topaz’. – An excellent variety with rich indigo-blue flowers.