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[UV, VIS] Rudbeckia - inside out

Dr Klaus Schmitt

Well-known member
Noticed today, how different the UV reflectance of a freshly unfolding flower (here Rudbeckia fulgida) could be, comparing the outside and inside of the flower petals. Totally invisible to the human naked eye, but surely not to pollinating insects!

Lumix GH1-UVIR, Cerco 94mm lens, Baader-U resp. UV/IR Cut filter

original.jpg


standardized UV color palette using ReflectionDisc:
original.jpg
 
Noticed today, how different the UV reflectance of a freshly unfolding flower (here Rudbeckia fulgida) could be, comparing the outside and inside of the flower petals. Totally invisible to the human naked eye, but surely not to pollinating insects!

Hi Klaus,

Isn't nature fascinating? How am I to read the interior's yellow on your UV scale? Is it a more saturated verion of (e.g. 360nm) brown?

Could it be that once the flower is fully in bloom, the UV reflection of the exterior petals changes?

Cheers,
Bart
 

Dr Klaus Schmitt

Well-known member
Bart, fascinating nature isn't it!?

The UV color palette was generated using monochromatic light to show how that sensor reacts to a certain wavelength. In nature there are non monochromatic UV reflections (at least I haven't found them yet), so the colors within an image will always be somewhat different and also the saturation and intensity will be different (which is not the case in that show palette).

So what I "read" from that image is, that the outside of the petals reflect around 380nm whereas the insides reflect around 360nm (makes sense, as bees peak sensitivity is around 360nm) - at that current stage this flower is in. It is part of a series of images I will do over a few days to see if the UV reflectance changes (my assumption is that it will).
 

Dr Klaus Schmitt

Well-known member
I have some theory about that different reflection:
I think it makes no (biological) sense that a flower attracts an insect when the flower is not ready yet, nor has anything rewarding to offer i.e. sending out (UV-) signals that would rather lead to "frustrated pollinators" which would most likely quickly learn not to visit such flowers anymore.

So, having the outside, less UV-reflective "shield" the opening flower, makes it less attractive to insects, unless the flower has fully opened and also has nectar, thus rewarding pollinators for their visit.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Klaus,

It would be interesting to see how this turns out in other plants.

something to look out for!

I wonder whether venus fly traps use UV signals to trick the prey to enter?

Asher
 

Asher Kelman

OPF Owner/Editor-in-Chief
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