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Page 110 · DO #4708 · 231_Rogers_Bx3FF31_r
- Collection
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David James Rogers (1918–2007) papers
- Item/Folder
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Graduate Students Garrido, Johnston, McArthur & McCarthy, 1974–1979
- Digital Object
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DO #4708,
page 110
- Collection-level dates
- 1948–1977
Page transcription
The chromosome numbers in Table 1 have been compiled from Dansereau (1955),
Gustafsson (1946-7), and a variety of other sources.
In several of the genera that Rydberg and others (e.g., Dansereau 1955)
have segregated from Potentilla, generative apomixis is unknown. All investigations of breeding structure in Pentaphylloides, Comarum, Drymocallis, and Argentina have shown them to be sexual, outcrossing, and self-incompatible; Pentaphylloides and Drymocallis are largely diploid (Løve 1954; Clausen, Keck,
& Hiesey 1940; Clausen & Hiesey 1958), whereas Comarum and Argentina are predominantly tetraploid with rare, sporadic populations at higher ploidy levels. The closely related genus Fragaria (probably closer to Potentilla s.s. than Pentaphylloides, Drymocallis, or Argentina are) is entirely sexual, outcrossing, and self-incompatible, with different widespread species at diploid, tetraploid, hexaploid, and octoploid levels (Staudt 1968). In Fragaria, there is a clear correlation between ploidy and degree of dioecy, the octoploids being completely dioecious; there is some evidence that the higher polyploidy in this genus has been produced by pre-meiotic reduplication of the chromosomes, which accords with the studies showing genetic segregation of several loci in the manner of autopolyploids (Staudt 1968, Asker 1971). In this regard, it is significant that all the intergeneric hybrids successful between Fragaria and Potentilla have been with species of Pentaphylloides and Drymocallis: the crosses attempted between Fragaria and Potentilla s.s. have all failed (Ellis 1962, Asker 1969). The breeding system of Potentilla s.s. seems strikingly different from that of related genera.
The chromosome numbers in Potentilla are mostly euploid, that is, at integral multiples of the basic number, x = 7. There is a small aneuploid series in the group Tormentillae, and long series with very high numbers in the groups Graciles and Multijugae; in these groups there have been no diploids or tetraploids reported. The chromosome numbers reported in Multijugae to date have been: