Polyploid Complexes in Relation to Ecology and the History of Floras

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Abstract
Polyploidy may serve as a valuable criterion for determining the relative age of different spp. and hence of the plant formations which they compose. This is because polyploids are always or nearly always derived from diploid ancestors. Three types of polyploidy are recognized; strict auto-polyploidy, allopolyploidy involving 2 or more distantly related spp., and a series of intermediate situations in which polyploids are derived from hybrids between closely related diploid spp. or subspp. The latter condition leads to the formation of the polyploid complex. An example is given in the species Eriogonum fasciculatum sens. lat. 3 entities are discussed. One diploid, sub sp. typicum (2n = 40), occurs in coastal Southern California and Lower California, and is adapted to a mild equable, semi-arid climate. Another sub sp.polifolium (2n = 40) occurs in the interior mountains and deserts of Southern California, and is adapted to a climate exhibiting extreme variations of temp. and a prolonged summer drought period. The third, sub sp.foliolosum (2n = 80), is common in the valleys of Southern California, and is the only form of E. fasciculatum found in the central Coast Ranges. It is intermediate in morphological characteristics and, judging from its distribution, combines the climatic tolerance of subspp. typicum and polifolium. Subsp. foliolosum occurs mainly in areas only recently uplifted from the sea, while the 2 tetraploids occur at least in part on older land. This situation is typical of polyploid complexes.