Noteworthy Allopolyploid Asters
Symphyotrichum subg. Ascendentes includes two allopolyploid species (Allen 1985, 1986) that are derived from species within subg. Symphyotrichum (x=8) and subg. Virgulus (x=5).
Symphyotrichum defoliatum (syn: Aster bernardinus) is also unique with a base number of x2=18 (13+5) having its origin in a putative back-cross allopolyploid event between S. ascendens and S. falcatum. It is native to southern California.
Also in southern California, Allen (1986) found additional allopolyploid populations with a chromosome number 2n = 42 (x = 21) that resulted from a backcross: S. ascendens (n=13) × S. spathulatum (n=8). Plants were insufficiently distinct morphologically from S. ascendens to allow recognition of a separate species.