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UltravioletPhotography

Cistus incanus [Hairy Rockrose]


Andrea B.

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Blum, A.G. (2014) Cistus incanus L. (Cistaceae) Hairy Rockrose. Flowers photographed in visible and ultraviolet light. http://www.ultraviol...hairy-rockrose/

 

Boyce Thompson Arboretum, Superior, Arizona, USA

24 April 2013

Wildflower in botanical garden

 

Synonyms:

  • Cistus villosus
  • Cistus creticus
  • לוטם שעיר (Hebrew)
  • لبّـاد أحمر (Arabic)

Comment:

C. incanus leaves have glandular hairs which produce ladanum, a resin used in perfumes and incense. This was known to the Greek Herodutus in the 400s B.C.E. and is thought to be the Balm of Gilead mentioned in the Bible.

C. incanus is a plant of the Middle East and Mediterranean. It has naturalized in some areas of California. The petals keep their wrinkled look.

In UV each C. incanus petal has a large UV-dark, feathered, basal blotch against the UV-reflective corolla. The blotches form a central flower within a flower. There are also some UV-dark striations on the bright areas.

 

Reference:

1. Jepson eFlora (2014) C. incanus L. Jepson Herbarium, U. of Cal.-Berkeley, Berkeley, CA. http://ucjeps.berkel...JM.pl?tid=19512

 

Equipment [Nikon D600-broadband + Nikon 105mm f/4.5 UV-Nikkor]

 

Visible Light [f/3.5 for 1/2000" @ ISO 200 with Nikon Coolpix A]

First bloom in a large stand of C. incanus.

cistusVillosusVisSun_042413boyceThomArbSupAZ_691pfPnRes.jpg

 

Visible Light [f/16 for 1/250" @ ISO 400 in Sunlight with Baader UVIR-Block Filter]

cistusVillosusVisSun_042413boyceThomArbSupAZ_9162pfPnRes.jpg

 

Ultraviolet Light [f/16 for 1/100" @ ISO 400 with SB-14 UV-modified Flash and Baader UV-Pass Filter]

cistusVillosusUVBaadSB14_042413boyceThomArbSupAZ_9170proofPnCrop.jpg

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Wow. This one turns black & white. Interesting.

 

There are also some UV-dark striations on the bright areas.

 

 

Hmmm. I have grown to increasingly suspect that such "striations" within the bright part of petals are not actual UV characteristics of the flower, but rather a result of "creases" (tiny "ruffles" or deeply-indented textured surfaces, like "micro-canyons") which cause reflected UV energy to bend in a different direction. In other words, a UV "shadow" area, caused by the steep angles produced by such fine creasing, and not the actual physical traits of the flower. This hunch of mine could probably be tested, if there were some possible way to "flatten" the petals out (eliminated the tiny creases or "micro-canyons" indented into the petals), then retake the photo and examine if the "striations" disappear from the image.

 

(Of course, it is probably not feasible to do such a thing: "Flatten out" the petals.)

 

I could be easily wrong with this hunch, but just thoughts to ponder.

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This is a reasonable speculation, Igor.

 

There is indeed sometimes a simple dark shadow in a fold, crevice or "micro-canyon" of a petal when photographed in UV. Always make test shots at different angles and distances to test this while actually shooting.

 

This is advice which I myself need to remember. Sometimes I get too eager when confronted with a gazillion flowers in a botanical garden. I get my one good UV shot and move on to the next - forgetting to make some other documentary frames.

 

Very importantly, there is also to consider the iridescence effect from conical cells on the surface of a petal. This can make some parts of the petal appear light/dark in UV in opposition to the "actual" lightness/darkness. This Cistus may have its striation darkness caused by the placement of its conical cells.

 

The crocus flower is a prime example of the conical cell effect. It is a very UV-dark flower, but will always show large parts as UV-bright because of the strong effect from the conical cells which scatter the UV light. If the areas of lightness/darkness change with respect to angle of illumination or with angle of view, then you most likely have conical cell iridescence at play.

 

In the case of this Rockrose, strong UV-flash seems to indicate that the striations are not shadows.

 

In the abstract of the following reference, surface striations are mentioned. I would like to get a reprint of this article.

 

Pigment distribution, light reflection and cell structure in petals

Q. O. N. KAY, H. S. DAOUD and C. H. STIRTON

Article first published online: 28 JUN 2008

http://onlinelibrary...0129.x/abstract

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A few close-ups taken from different vantage points will (literally) throw light on this issue. Iridescence tends to make the corolla mottled or variegated such that some areas are bright, others are dark, and some are simply perceived matted or fuzzy.

 

Plenty of UV-bright flowers have UV-dark stripes or veins on their petals. Geranium is one out of many examples.

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Do you have a way to get a reprint of that paper, Bjørn?

I just spent an hour trying to track down Charles Stirton who is now in England. But not active at a University any longer, so no way to contact him for a reprint.

 

from the Abstract (bullet points and blue added by me):

 

Six basic kinds of petal epidermis anatomy were found, sometimes in combination;

  • papillate (112 species) and multiple-papillate (13 species),
    in which the conical-papillate form of the cells traps incident light and scatters emergent light,
    with surface striations aiding these functions in many cases;
  • reversed-papillate (4 species),
  • multiple reversed-papillate (29 species),
  • lenticular (32 species) and
  • flat (11 species),
    all with surface striations in some cases.

Light is usually reflected from petals mainly by an aerenchymatous unpigmented reflective mesophyll;

in certain species this is replaced by a reflective layer of starch grains in the upper mesophyll.

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This is very useful and valuable information, friends.

 

Thank you for posting those additions. Like I keep saying: I learn something new every day.

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