Rosa, DC.

I. Klášterský, 1968, 10. Rosa L., Flora Europaea, Volume 2, Rosaceae to Umbelliferae, Cambrdige: Cambridge University Press, pp. 35-42: 28

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Sect, caninae DC.  

Deciduous shrubs, with erect or arching stems. Rhizome short. Prickles usually numerous, hooked or straight; acicles usually absent. Flowers in bracteate corymbs. Outer sepals usually pinnatifid, deflexed, erect or patent, persistent or caducous after anthesis. Disc flat or conical, variable in size, narrow. Carpels long-stipitate. Styles free.

This section has long been recognized as critical, and very large numbers of taxa have been described. So far as is known, they are all polyploid, with 2n = 28, 35 or 42, and their reproduction is unusual. In the pentaploids, for example, 7 bivalents and 21 univalents are formed at meiosis. In the pollen the univalents are lost, so that most functional pollen-grains carry only 7 chromosomes; in the ovules, on the other hand, all the univalents go to one pole at the first meiotic division and the egg has 28 chromosomes. Thus, in sexual reproduction, most of the chromosomes of the offspring come from the seed-parent and have not paired at meiosis. Inheritance thus tends to be predominantly maternal, and this in turn means there is a tendency for the biotypes in Sect. Caninae   to be relatively constant, though hybridization can produce new biotypes, some of which may survive and become stabilized. The situation is analogous to facultative apomixis, though Rosa is not apomictic.

In the account of Sect. Caninae   which follows, an attempt has been made to cover the whole range of variation but to describe only a limited number of fairly well-defined species. It is recognized that many intermediates may occur. Because of the taxonomic difficulties, the geographical distribution of many of the species is imperfectly known, and can only be given in general terms.