Experimental Evidence for Systematic Placement of the Haplopappus phyllocephalus Complex (Compositae)

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Abstract
The Haplopappus phyllocephalus group consists of H. aureus Gray, H. annuus (Rydb.) Cory, and H. phyllocephalus DC. All are annuals with x = 6, campanulate involucres, and ray florets and were previously placed in H. M. Hall''s sect. Blepharodon. As a representative of the group, H. aureus was crossed to H. venetus H.B.K. subsp. venetus of sect. Isocoma, which consists of shrubs with x = 6, generally turbinate heads, and no rays. F-1 hybrids were vigorous and chiasma frequency was only slightly reduced. However, chiasma frequency and pollen fertility were not much reduced from that found in hybrids within the phyllocephalus group. Presence/absence of ray florets is controlled by a single dominant/recessive gene locus; a 3:1 ratio of rayed to rayless was found in 67 F-2 plants. The two groups have in common the same chromosome number and abruptly constricted disc florets and are now considered to be closely related and members of the same section of the genus, i.e., sect. Isocama.