The Plantsman 6 (2): 123-4. (1984)
ORIGIN OF BOURSAULT ROSES
E. F. Allen and A. V. Roberts

THE BOURSAULT roses form an interesting small group of hybrids developed early in the last century. They are commonly said to have been the results of the cross R. pendulina x R. chinensis but Ann Wylie (1955) has written 'the existing varieties which have been examined are diploid, hence R. pendulina (tetraploid) can hardly have been one parent'. In this paper we re-examine the evidence for the origin of these roses and present chromosome counts for three cultivars.

William Paul (1848) listed seven Boursault varieties, all with double or semi double flowers. He described the shoots as long, flexible, very smooth, in some instances entirely free from thorns. They resemble R. pendulina in the bare shoots being markedly red in winter. Of the four or five cultivars which have survived to the present day three can be recognised as being included in Paul's list. They are 'Amadis', with crimson purple flowers, 'Blush Boursault' (syn. 'Calypso'), which is grown as a wall climber at Melford Hall, Long Melford, Suffolk; and 'Inermis', which we now call 'Morletti' (also 'Morlettii') a fine vigorous shrub of which three specimens are grown in the Royal National Rose Society's gardens, at St Albans, in the South Border. Also cultivated at St Albans is the early flowering 'Mme de Sancy de Parabere', described with such enthusiasm by Tess Allen (1965) and well illustrated by E. F. Allen (1973). A fifth variety is possibly distinct from 'Amadis' but, as grown at Copdock, its foliage colours very much better in autumn. This, however, may be a cultural character.

Cytology

Squash preparations were made from root or shoot meristems using the Feulgen staining procedure (Darlington and La Cour 1963), in conjunction with phase contrast microscopy. Before fixation, meristems were immersed in 0.1% colchicine solution for three hours.

The Boursault cultivars Morletti and Madame Sancy de Parabere were both diploid (2n=14). This result seems to exclude R. pendulina (tetraploid) X R. chinensis as their parentage as had been previously suggested. However, it is noted that the first generation derivative of this cross was the single-flowered R. x reclinata which had this parentage and that the 'Rosier Boursault' was a seedling raised from it, both having been raised by Cugnot. Thory further states that both of these hybrid roses had flowers of a delicate pink; they differed only in the one having single flowers while the other had a score of petals. By contrast Paul describes the Boursault as having 'flowers bright cherry when first opening, gradually becoming paler'.

Rowley (1960) found that three triploid Hybrid Musk cultivars set abundant crops of hips and that many other triploid cultivars are capable of setting moderate crops. Wulff (1959) demonstrated that diploids can arise as progeny of a triploid. Of one of the two fertile triploid roses studied by Wulff, he wrote, 'the further course of the reduction division is highly irregular. A pronounced elimination of chromosomes occurs, and the viable pollen grain and eggs cells of this triploid rose evidently received only seen chromosomes, for its offspring (six plants) were diploid'. It seems reasonable to suggest, therefore, that the diploid Boursault roses arose from a probable triploid R. x reclinata by a similar process.

It is not known if the single flowered R. x reclinata remained in cultivation long enough to have produced all of these hybrids. If not then some of the later ones, such as 'Mme de Sancy de Parabere', may have been seedlings from either the original Rosier Boursault or its progeny. Certainly 'Morletti' seems to produce a little good pollen and sometimes the occasional ripe fruit so perhaps this hybrid would merit the attention of rose breeders. Its flowers have a little scent and the bush is long lived and extremely hardy.

There remains the problem of the rose sometimes sold as "Rosa pendulina plena", which has been found also to be diploid. This has pale pink, semi double flowers (Tess Allen 1965) and the stem bases are spiny. Were it not for its sterility, it might have been considered as a possible parent of the Boursault roses, which it certainly resembles. On the evidence of its ploidy, it appears less likely to be a variety of the species R. pendulina, than a Boursault which needs a cultivar name.

References