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A CYTOGEOGRAPHIC STUDY OF CHAENACTIS DOUGLASII (COMPOSITAE, HELENIEAE)
Author(s) -
Mooring John S.
Publication year - 1980
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1980.tb07763.x
Subject(s) - ploidy , biology , polyploid , meiosis , hybrid , range (aeronautics) , population , glacial period , botany , chromosome , salamandridae , ecology , caudata , genetics , paleontology , materials science , demography , sociology , gene , composite material
Analysis of 512 plants derived from 200 populations shows that the widely distributed western North American Chaenactis douglasii species‐complex consists of diploids ( n = 6), triploids, tetraploids, and hexaploids. Microsporocytes were the source of most of the chromosome counts. About 9% of all plants examined had one or more full‐sized extra chromosomes. Multivalents, usually a ring or chain of four chromosomes, were almost entirely restricted to polyploids, where one or more were identified in 38% of the tetraploids and 33% of the hexaploids. With two exceptions, diploids and polyploids were not found in the same population. Frequencies of diploid, triploid, tetraploid, and hexaploid populations were, respectively, 34, 1.5, 55 and 9.5%. With significant exceptions, diploid populations predominate in the Pacific and Rocky Mountain Systems, whereas polyploid ones are most frequent in the intervening plateaus. Ploidy level is correlated with age of substrate, rather than with climate, elevation, vegetation, or soil type. Range, morphology, ploidy level, and meiotic behavior suggest that var. achilleifolia tetraploids and hexaploids are descendents of hybrids between other variants of the complex. The diploid‐tetraploid‐hexaploid geographic distribution and the age of the substrates where each tends to occur suggest that the complex evolved in late Cenozoic time in response to major climatic and geologic changes that induced migration and hybridization. The hybrid derivatives, stabilized by polyploidy and tolerant of increasing aridity, came to occupy newly available habitats in areas disturbed by volcanic activity and glacial or glacial‐related processes.