Philadelphus mexicanus Schlecht.

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P coulteri S. Wats

This species, which is probably not in cultivation, differs from P. mexicanus in its acute or obtuse, not acuminate leaves, and in having the calyx and pedicels densely covered with white hairs. Native of Mexico. For P. coulteri Hort., see P. mexicanus ‘Rose Syringa’. A plant grown under the name P. coulteri was used by Lemoine in creating the hybrids of the Purpureo-maculatus group and was distributed by him commercially. The Irish gardener W. H. Gumbleton received a plant from Lemoine under the name P. coulteri in 1893. This flowered in 1896, and from his description it would seem that Lemoine’s P. coulteri was, like ‘Rose Syringa’, a blotched form of P. mexicanus. Gumbleton added: ‘I believe M. Lemoine has used this new Philadelphus for crossing with other varieties… but none of his seedlings from these crosses has yet flowered’. (Gard. Chron., Vol. 19 (1896), p. 752.)

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P maculatus (Hitchcock) S. Y. Hu

This species or natural hybrid is probably not in cultivation and is only mentioned because Dr Hu, in her monograph on Philadelphus, states positively that the Rose Syringa of Irish gardens belongs to P. maculatus. In fact, this plant differs from P. maculatus in every way that P. mexicanus does.

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'Rose Syringa'

Petals mostly with a purplish-pink mark at the base (P. coulteri Hort., not S. Wats.; P. mexicanus var. coulteri Burbidge). This philadelphus first came to botanical notice in 1891, when F. W. Burbidge, Curator of the Trinity College Botanic Garden, Dublin, sent a specimen to Kew. In the accompanying letter he wrote: ‘Can you kindly give me the name of the enclosed? I cannot find it in the books. It exists in one or two old gardens here, where it is called Rose Syringa. Its sweet fragrance and purple-centred flowers are remarkable.’ What reply he received is not known, but writing some years later in The Gardeners’ Chronicle he referred to this plant as P. mexicanus coulteri and it is by this name, or as P. coulteri, that this philadelphus has been grown for the past seventy years. In fact, it is not P. coulteri S. Wats.; nor is it P. maculatus (Hitchc.) S. Y. Hu, as has recently been suggested (see below). Burbidge quite rightly referred to it as a variant of P. mexicanus, and was wrong only in identifying it with P. coulteri S. Wats.Since this philadelphus lacks a valid distinguishing name, it seems reasonable to take up the traditional garden name and call it ‘Rose Syringa’. The old plant at Tresco Abbey in the Isles of Scilly agrees in every detail with the example at Kew, except that the leaves are larger (up to 3 in. long), but this discrepancy can be explained by its greater size and vigour. These plants in turn agree with the Irish specimens in the Kew Herbarium. The origin of ‘Rose Syringa’ is not known, but it may well have been introduced by Hartweg at the same time as normal P. mexicanus. It agrees well with a specimen of this species collected by him and preserved in the Kew Herbarium, in which the flowers have a dark stain at the base, possibly indicating that they were blotched as in ‘Rose Syringa’. It is, however, very likely that the plants cultivated as P. coulteri are not the old variety of Irish gardens but a similar, perhaps indistinguishable, clone, distributed by Lemoine under that name (see further below).This variety is grown at Kew on the Temperate House Terrace and also in the University Botanic Garden, Cambridge, in a sheltered bay outside the greenhouses. In both gardens it makes a small plant, but would grow taller if there were room to train it.