Ultraviolet Flowers: Rudbeckia hirta

Rudbeckia hirta L.

Asteraceae

Visible light
(L37C filter)

UV light
(FF + CC20C, SB-140)

UV light
(U-360, SB-140, combined green and blue channels converted to B/W)

Nikon D1H, UV-Nikkor 105 mm f/4.5, @800 ISO

This species, one of the many species called "Black-Eyed Susan", native to North America and occurring only adventitious in Norway, has very prominently developed UV markings on the ray florets.

The inner two third of each ray flower strongly absorbs UV by the presence of flavonyl glucosides secreted by specialised epidermal cells. In the B/W image, it is readily apparent that UV absorbance is quite patchily distributed within the epidermis of the ray floret.