Cytological Study of Tetraploid Species of Magnolia subgenus Yulania (Magnoliaceae)

Cytological studies were conducted on five tetraploid species plus two varieties of Magnolia subgenus Yulania and a hybrid between two of these species. Two different chromosome configurations in meiosis are observed in this article. The first group was typical for M. acuminata, M. liliiflora and their relatives which share several cytological characteristics including chromosome configurations and behavior in meiosis. The cytological evidence indicate autotetraploid origin for these species, despite the homologous chromosomes likely having changed their structures causing the formation of heteromorphic multivalents, chromosome bridges and fragments during meiosis. The second group of chromosome configuration was found in M. cylindrica and M. concinna. These species were characterized by very rare trivalents and tetravalents. These observations suggest these taxa as allotetraploids which may have been formed from hybridisation between hexaploid and diploid parents as deduced from trivalents observed at some rate. Multivalent formation and possible translocations and inversions of chromosomes in M. liliiflora influence its propagation by causing low fertility. M. liliiflora is probably a comparatively new species with an unstable chromosome constitution and is growing only in small populations at low elevation. It is vulnerable, and the species could already be extinct in nature. On the other hand, M. acuminata shows a more regular chromosome behavior and fewer abortion spores than M. liliiflora, and should be a more stable species with longer evolution time. Thus, the superior fertility of M. acuminata has enabled it to develop a stable and extensive distribution from NE to SE USA.