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Using UV Light to Bring Out Surface Details

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#1 Andrea B.

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Posted 29 June 2021 - 00:03

It is well known to us here on UVP that Ultraviolet light brings out more surface details of a subject than does Visible light. Today I made use of this for a flower identification. I don't think any forensics teams are likely to need to identify flowers, but I'm sure they make use of UV light both as a surface enhancing light and as a fluorescence-inducing light to identify many other things.

The flower, a white Solanum from the Nightshade family.
Attached Image: solanumEleagnifoliumWhite_vis_flash_20210626elDorLosCompadres_24367.jpg



I found the white Solanum flower growing locally. I tried to ID it, but I could not find any white Solanum like this in my various New Mexico field guides or on the usual Southwestern botanical websites I consult. However, the flower, except for its white color, looked quite like the blue/lavender Solanum eleagnifolium I recently photographed.
LINK: Solanum eleagnifolium

After more stumbling around online, I eventually found that S. eleagnifolium could have a rare (or at least, very unusual) white variation. One key point of identification for S. eleagnifolium is the presence of stellate hairs on the back (abaxial) side of the flower. So I needed to look for that on the white flower to confirm the ID.

Yes, flowers and their stems and leaves can be hairy -- a fact which I did not appreciate fully when I started out on this UV botanical adventure. There are fifty-eleven zillion different kinds of flower/stem/leaf hairs and an entire dictionary's worth of jargon to describe them.
LINK: Trichome

But to stay on topic, a stellate (star-shaped) hair is actually a circular array of hairs growing from a center point. So I needed to consult the photos of the back side of the flower to look for stellate hairs.
LINK: Google search for images of Stellate Hair

The abaxial side of S. eleagnifolium.
Attached Image: solanumEleagnifoliumWhite_vis_skylight_20210626elDorLosCompadres_24414pnBig.jpg



I zoomed in on the topmost point of the white flower to begin looking. Here is a crop of that portion of the corolla which has not been resized. Nothing starry is immediately obvious. So I added some sharpening but still was not able to clearly make out anything stellate except perhaps in one location.
Left: Unresized crop, Visible. Right: Sharpened, unresized crop, Visible.
I can make out one stellate hair in both photos. Do you see it?
Attached Image: solanumEleagnifoliumWhite_vis_skylight_20210626elDorLosCompadres_24414pnCrop.jpgAttached Image: solanumEleagnifoliumWhite_vis_skylight_20210626elDorLosCompadres_24414pnCropHiPass.jpg



Ultraviolet to the rescue! In the corresponding unresized, unsharpened crop from the UV version of the white flower, those stellate hairs were immediately obvious. A locally sharpened (brushed in over the hair clumps) version is also shown, but was not really necessary.
Left: Unresized crop, UV. Right: Sharpened, unresized crop, UV.
At least 20 stellate hairs are easily visible.
Attached Image: solanumEleagnifoliumWhite_uvBaad_sb140_20210626elDorLosCompadres_24418Crop.jpgAttached Image: solanumEleagnifoliumWhite_uvBaad_sb140_20210626elDorLosCompadres_24418CropShrp.jpg


Conclusion: Given that all morphological characteristics, including stellate hairs, matched between the blue and the white Solanums, I could safely say that I had the rare white variant of Solanum eleagnifolium.


Side Note: UV light is used industrially with CCD cameras to inspect surfaces of materials for quality control. Most of the lenses sold for such industrial use are not chromatically corrected and thus not too useful for broadband UV photography.
Andrea G. Blum
Often found hanging out with flowers & bees.

#2 Andy Perrin

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Posted 29 June 2021 - 01:57

Nifty use of UV!

Andrea, back in 2016, I discovered some kind of white nightshade that looks very similar, except mine didn't just have hairs — it had VICIOUS needle-thin thorns! A truly deadly nightshade.

Here are my pics:

Attached Image: IMG_3569 vis1.jpg

Attached Image: IMG_3566 vis2.jpg

Attached Image: DSC02073 UVP.jpg

Attached Image: DSC02098 UVP.jpg

Edited by Andy Perrin, 29 June 2021 - 02:02.


#3 colinbm

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Posted 29 June 2021 - 02:52

'Don't tread on me'
Good, thanks for showing Andrea & Andy

#4 UlfW

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Posted 29 June 2021 - 07:00

There is even flowers with very hairy reproductive parts.
At first I thought it was mould, but looking them up in the flora I found out that it was normal.
A few years ago I have identified it as some kind of Verbascum and now forgotten exactly what sort.
Filter: a BG3-S8612 stack
Attached Image: Screen Shot 2021-06-29 at 08.43.46.png

Edited by UlfW, 29 June 2021 - 07:01.

Ulf Wilhelmson
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#5 Andrea B.

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Posted 29 June 2021 - 19:44

Andy, that is Horsenettle, Solanum carolinense, which can be lavender or white, neither color rare.

Make a botanical post with it if you have time entitled: Solanum carolinense [Horsenettle]: White
The Horsenettle I posted a couple of years ago is Lavender.


Ulf, that is really a lot of hair! Have you made a botanical post for it?
Andrea G. Blum
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#6 UlfW

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Posted 30 June 2021 - 08:19

No, I don't think so.

I think that the plant is a Verbascum speciosum Schrad, Hungarian Mullein.
At first I feared that it was the, here protected, Verbascum lychnitis L, White Mullein, but ruled out that possibility.

I will check if the images I have are good enough for a formal botanical post.
If I remember correctly there are some focus issues for different filter-combinations.
I wanted to redo photographing this flower later by stacking and using my less noisy Sony A7III.

There is no entry of this species in the botanical section yet.

Edited by UlfW, 30 June 2021 - 08:29.

Ulf Wilhelmson
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#7 nfoto

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Posted 30 June 2021 - 08:33

With no disrespect to Andrea's initial post, albino forms of flowers are not very unusual. A lot of red- or blue-coloured flowers show this variation, as colour coding and development apparently is controlled by a very small subset of genes (even 1?).

The approach of using UV to "throw light" (pun intended) on enigmatic surface details is highly recommended of course.

#8 Andy Perrin

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Posted 30 June 2021 - 16:52

Ulf, I think you misread Andrea’s reply. My flower is the Solanum carolinense, not yours. She did not ID yours.

#9 UlfW

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Posted 30 June 2021 - 19:27

No Andy that I understood directly.
I was only referring to the hairy flower in my picture, that I identified again.
The "No I don't think so" was about making a botanical post of it.
Sorry for my confusing answer.
Ulf Wilhelmson
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#10 Andrea B.

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Posted 01 July 2021 - 17:23

Birna: With no disrespect to Andrea's initial post, albino forms of flowers are not very unusual.

Agreed, generally speaking.
But my New Mexico floras and field guides do mention the "rarity" of the white version for this particular Solanum. Our local roadsides are rampant with the blue S. eleagnifolium. But I've only seen the white version this once in a small location.
Andrea G. Blum
Often found hanging out with flowers & bees.