1831 xvi. 207 The flowers..having their rays ligulate, and the disk flowers tubular.
1870 J. D. Hooker 185 Asteroideæ..Disk-flowers 2-sexual.
1954 C. J. Hylander 453 The conical receptacle..bears disk-flowers which are purplish in colour.
2006 187 42/2 If the head was flowering, we further recorded the stage of the disk flowers.