Osteospermum hyoseroides [Dassiegousblom]

[nfoto]

Rørslett, B. 2022. Osteospermum hyoseroides (DC.) Norl. (Asteraceae). Dassiegousblom. South-African flowers photographed in ultraviolet (UV) and visible light. LINK

Photographed near Kamiesberg, Northern Cape, where it grew on dry slopes of upland hills.

 

This species is found in the Cape Provinces (map from http://www.ville-ge.ch/musinfo/bd/cjb/africa/details.php?langue=an&id=100239),

 

 

The habit is a small, straggling herb with deep yellow flower heads,

 

The flower head seems from below,

 

The orange hue is more visible on the underside of the ligules.

 

Seen in ultraviolet (UV), the ligules have a UV-dark basal patch, and this pattern repeats for the corolla of the disc florets. The anther column likewise is UV-dark, whilst the pollen appears much brighter.

 

 

The underside of the ligules have 5 distinct UV-dark stripes. The phyllaries are quite UV-dark as well,

 

 

 

All photographs on this page are copyright Birna Rørslett and may not be used without explicit permission from the author.

 

Literature for species identification:

SNIJMAN, D.A. (ed.). 2013. Plants of the Greater Cape Floristic Region, Vol. 2: the Extra Cape
flora. Strelitzia 30. South African National Biodiversity Institute, Pretoria.

 

[Published 13 February, 2022]

 

 

[Andrea B.]

Another pretty dual bulls-eye.

[Wayne Harridge]

Thanks for this and the other postings over the last week of these plants from South Africa.  I was just wondering, from the colours recorded on the images is it possible to map back to the reflectance spectrum of particular parts of the flowers?  What do you use as the basis for white balancing these images?  I notice that foliage always seems to display as various shades of grey.

[nfoto]

To the first question, don't go there as it is like opening a can of worms. Or worse.

 

For the "UV white" balance, I  use a disc of white PTFE ('Teflon'), which reflects fairly flat across the UV band of interest.

 

Foliage is usually grey in UV, but can be very dark almost jet black. Sometimes leaves are very bright however, usually when there is a cover of hair on them.

[Fandyus]

I can't wait for my a6000 to get back. I'll get some yellow flowers over at the florist's and do something similar :)

[Andrea B.]

Wayne, you can read about white balancing here: 

<> Sticky :: White Balance in UV/IR Photography <>

 

As for the other question...

The UV waveband in which we photograph with our broadband UV-pass filters is only 100 nm wide. Wideband UV-pass filters usually peak around 350-360 nm. UV in sunlight rapidly drops from a peak at 400nm to almost nothing at 300nm. So the typical reflected UV photo we post here is typically representing mostly the upper half between 350-400 nm. To attempt to match a UV false color to a particular reflected wavelength within a 50nm band is really not easy. Nor can it ever be accurate. Setting a white balance depends on the converter, filter, camera, lens, choice of white balance material and more. Also the reflected wavelength may be affected by iridescence or prismatic effects of the subject or other characteristics. Nevertheless, we do have some topics here on UVP where one of our scientist members has attempted to match raw color to reflected wavelength. Let me go find links and put them here: 

LINK1  LINK2

[Wayne Harridge]

On 2/16/2022 at 8:04 AM, Andrea B. said:

Wayne, you can read about white balancing here: 

<> Sticky :: White Balance in UV/IR Photography <>

 

As for the other question...

The UV waveband in which we photograph with our broadband UV-pass filters is only 100 nm wide. Wideband UV-pass filters usually peak around 350-360 nm. UV in sunlight rapidly drops from a peak at 400nm to almost nothing at 300nm. So the typical reflected UV photo we post here is typically representing mostly the upper half between 350-400 nm. To attempt to match a UV false color to a particular reflected wavelength within a 50nm band is really not easy. Nor can it ever be accurate. Setting a white balance depends on the converter, filter, camera, lens, choice of white balance material and more. Also the reflected wavelength may be affected by iridescence or prismatic effects of the subject or other characteristics. Nevertheless, we do have some topics here on UVP where one of our scientist members has attempted to match raw color to reflected wavelength. Let me go find links and put them here: 

LINK1  LINK2

Thanks for those links Andrea, quite a lot to wade through, it helps that I majored in physics.  I now have a good understanding of the problem of mapping false colours to UV wavelengths so I think I'll just enjoy the colours I see and leave it at that.  I have a PTFE target and I'm able to white balance to that easily enough now after a bit of "playing around" with a few raw converters - this gives the characteristic grey foliage.

[Doug A]

@nfoto I like that you also capture the underside of the flower. It adds a lot of information about the plant. This is a special plant with bullseye and stripes.

 

Thanks for sharing,

 

Doug A