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Opuntia Microdasys [Bunny Ears Pricklypear]

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#1 Andrea B.

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Posted 03 May 2018 - 23:34

Blum, A.G. (2018) Opuntia microdasys (Lehm.) Lehm. ex Pfeiff. (Cactaceae) Bunny Ears Pricklypear. Flowers photographed in ultraviolet and visible light. http://www.ultraviol...rs-pricklypear/

Desert Botanical Garden, Phoenix, Arizona, USA
22 Apr 2013
Wildflower in botanical garden

Synonym:
  • Cactus microdasys Lehm.
  • Opuntia macrocalyx Griffiths
  • Opuntia pulvinata DC
Other Common Names:
  • Polka Dot Cactus
  • Golden Bristle Cactus
Comment:
Native to Northern Mexico, this cactus has abundant yellow flowers with a contrasting bright green stigma. In Ultraviolet light, the lighter anthers and pollen stand out somewhat against the UV-dark petals. There is some strong iridescence in the petals, here seen in the base of the flower.

Reference:
1. Desert Botanical Garden (2013) Phoenix, Arizona, USA.
Attached Image: opuntiaMicrodasys_vis_flash_20130422desBotGardPhxAZ_228pn.jpg


Equipment [Nikon D600-broadband + Nikon 105mm f/4.5 UV-Nikkor]
Unless otherwise noted.

Visible Light [f/6.3 for 1/1250" @ ISO-100 in Sunlight with Coolpix A]
Attached Image: opuntiaMicrodasys_vis_sun_20130422desBotGardPhxAZ_233pn.jpg

Visible Light [f/11 for 1/160" @ ISO-100 in Sunlight with Baader UVIR-Block Filter]
Attached Image: opuntiaMicrodasys_vis_sun_20130422desBotGardPhxAZ_7593pn.jpg

Ultraviolet Light [f/11 for 1/2.5" @ ISO-400 with SB-14 UV-modified Flash and BaaderU UV-Pass Filter]
The interior of the very UV-dark flower was slightly lightened to better show the flower structure.
Attached Image: opuntiaMicrodasys_uvBaader_sb14_20130422desBotGardPhxAZ_7603pn2.jpg
Andrea G. Blum
Often found hanging out with flowers & bees.

#2 OlDoinyo

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Posted 04 May 2018 - 21:41

The flower is pretty much straight UV-dark, except for some long-wave reflectance around the stamens. What does this tell us about pollination? I seem to recall that some cacti are moth-pollinated.

#3 Andrea B.

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Posted 05 May 2018 - 04:54

There are indeed some night-blooming cacti which are pollinated by moths or by bats. The big Saguaros in Arizona are in that category.

Most of the big bowl shaped, day-blooming cactus flowers like in this photo are bee pollinated according to my various desert flower field guides. These flowers are alway swarming with beetles and bugs down in the base of the flower which they use as a temporary shelter. But it is the bees who get the actual pollination job done because they bump against the flower stigmas as they travel from flower to flower.

The UV photo is only one "channel" of bee vision. The bee does not see that cactus flower as dark. It is getting some visual stimulation from the reflected yellow and probably seeing the flower as a green or yellow-green.
Added: That is speculation on my part based on my own explorations of bee vision.
Andrea G. Blum
Often found hanging out with flowers & bees.