The highest correlation was found between corolla diameter and flower tube length (0.53), which was also the only one being significantly different from zero.

P. S. Masinde, Ceropegia ahmarensis (Asclepiadaceae: Stapelieae), a New Species from Somalia, Kew Bulletin, Vol. 55, No. 1 (2000), pp. 225-228 ...

Jeff Mitton Natural Selections. Most of the 200 species of Castilleja share a common flower form and are easily recognized as Indian paintbrush, but I did not recognize painted cup as a paintbrush.