Iowa State Journal of Science: Volume 35, pp. 255-256 (1960)
Some notes on the use of Rosa laxa as a source of hardiness in rose breeding
Griffith Buck

The tetraploid species, Rosa laxa, Retzius, which is indigenous to the dry steppes of central Siberia, is such a species. It has never been a popular garden subject, for it is lacking in many of the qualities demanded of ornamentals. The plants of R. laxa which are currently available in the United States have been derived by seed and asexual propagation from plants grown from seed collected by Hansen in the Altai region of Siberia in 1913. This collection was given the name 'Semi' to distinguish it from earlier ones. This species is closely allied to R. cinnamomea and is included in the section Cinnamomeae. The name 'laxa' has been given erroneously to two other roses; one, a form of R. blanda and the other, a form of R. canina. Seedling populations of R. laxa show variation in plant height, degree of armature, presence and degree of pubescence on the foliage, and degree of remontance. Plant habit, flower color, foliage retention, disease tolerance, and hardiness are remarkably constant characteristics. The plants are very hardy, having survived, without protection of any kind, -30 °F. without injury. The plants are erect, vigorous, and range in height from four to eight feet. The young canes are yellow-green, changing to greenish-yellow with maturity. Bristles are plentiful on the basal portion of the canes. The flowering canes are free of bristles but have paired, curved infrastipular spines. Suckering is moderate. The large foliage is moderately susceptible to rose blackspot and tolerant of powdery mildew. However, the foliage matures and is lost early so that the plants are bare, except for the immature growth at the tips of the canes, by mid-September. The two-inch, five-petalled, white flowers are borne in clusters of five, terminally on lateral shoots arising from canes of the previous season's growth. Flowers later in the season are borne on secondary laterals from stems bearing the June bloom. Although the plants flower profusely in late May and continue intermittently until frost, the small size of the flower and flower cluster contribute to the effect of sparseness.