The ligules of Coreopsis basalis bear an attractive reddish-brown spot at the base. The spot has been used as a taxonomic character of the species. But there is variation within populations at any one time, and within individuals at sequential times, for the size of the spot. A few individuals lack the ligule spot entirely. Variation in average ligule spot size in greenhouse-grown populations of C. basalis and an artificial hybrid is described. Average spot size declines as the blooming season progresses. Some individuals with spotted ligules early in the season bore spotless ligules late in the season. No correlation was found between the spot size and ordinary environmental parameters. The dependability of the ligule spot as a taxonomic character declines as the blooming season progresses.
Smith, Edwin B.
"Variation in Ligule Spotting in Coreopsis basalis,"
Journal of the Arkansas Academy of Science: Vol. 28
, Article 25.
Available at: http://scholarworks.uark.edu/jaas/vol28/iss1/25