Picea pungens

Bryant wrote and contributed the photograph for today’s entry. It’s my fault it’s late in being posted, but I’ve been catching up since going on a collecting foray late last week. He writes:

Continuing with the series on colour, I thought I would dip into the more structural side of things. In particular, I want to focus on blue colouration in foliage. Today’s photo is of a compact blue-needled selection of Picea pungens, taken in the E.H. Lohbrunner Alpine Garden here at UBC. Picea pungens is a high-altitude species, which grows at elevations between 1,750-3,000 meters in the southern Rocky Mountains. I chose this species because I was intrigued by David Lee’s fascination with blue foliage as described in his book, Nature’s Palette. Lee’s focus is mainly on iridescent blues found in tropical species such as Selaginella willdenowii.

The more subtle blue hues that are found in Picea pungens (commonly the Colorado blue spruce) are not produced by modified anthocyanin pigmentation like the blues found in many flowers. Species like the blue spruce produce a thin film of epicuticular surface waxes on their needles. These deposits diffract light at short wavelengths, which we perceive as a pale blue. This scattering of radiation is a physical phenomenon known as Tyndall scattering–the same reason why the sky and ocean are blue. The surface waxes are thought to reduce the absorption of photosynthetically-active radiation, reduce transpiration, influence gas exchange and lower leaf temperature (see: Physiological Effects of Surface Waxes). These results caused by the diffraction of light by epicuticular surface waxes can be advantageous or disadvantageous depending on the biogeoclimatic location of the individual.

In the case of the Selaginella examined by Lee, the multiple layers of convexly-shaped epidermal cells are what cause the diffraction of a more iridescent blue colour on the leaves. Selaginella willdenowii is a shade-dwelling plant, and the blue iridescence is only found on leaves that are rarely exposed to sunlight. Lee was curious as to why the fern would evolve structures that diffract much of the scarce light that is available to them. After thirty years of pondering this question, Lee’s explanation is that the iridescent shade leaves deflect short wave radiation and are thus able to absorb more long wave radiation. This is advantageous in the shaded understory of tropical rain forests, because long wavelength radiation is more available than short wavelength under the canopy.

Picea pungens

14 responses to “Picea pungens”

  1. James Singer

    The most beautiful of all “blue” plants–it’s like moonlight.
    Bismarckia noblis11c.jpg

  2. Lucinda

    Fascinating! Thank you!

  3. wendy

    Britain is after all known for its rainy dark climate… could we be on the track of the deeper reason why ancient Britons painted themselves blue?

  4. Sue Frisch

    Fascinating! How about the blues in grasses? Some of them are very pale blue.

  5. Deb Lievens

    Bryant, Excellent post. Ah, the physics of botany. You’ve given us a lot of good info to absorb. How about the reflective green of Schistostega pennata?
    By the way, can you tell me how to find the rest of your color series? I tried going to “tags” but couldn’t find anything there. I am a loyal reader, but sometimes I miss things. Thanks.

  6. Wes

    Ahhhhn yes…. those of us who make fresh christmas greenery learned long ago that using a waxy antidesicant (wiltpruf) on blue spruce foilage killed the “blue”. It keeps well in outdoor wreaths anyway.
    Same applies to Juniperous Virginiana berries…. you lose that wonderful light blue color if you treat them (you do get a somewhat less wonderful dark blue though (anthracynins showing thru).
    Thanks, for the thoughts

  7. Newman

    Love the Blue Series, that should take you a while 🙂

  8. Daniel Mosquin

    Deb, it’s the first tag — “colours in plants” series.

  9. Ginny

    Such an interesting write-up! David Lee’s book has been in my to-be-read pile for a few months; now I’m inspired to pull it out and put it on top.
    Many thanks to Bryant and Daniel.

  10. Ron B

    So nobody at the garden knows the cultivar of the spruce?

  11. Daniel Mosquin

    Ron — no, we do not. It was received as an unrooted cutting from the US National Arboretum somewhere around 1976. It came to us as Picea pungens ‘Compacta’, but as the folks at Coenosium Gardens explain, that cultivar is green, and has been lost to cultivation. We do have the US National Arboretum’s accession number: NA.21325.

  12. Ron B

    Probably from the Gotelli collection, home of assorted questionable identifications. I find no record of that accession on the USNA web site now, the only Picea pungens listed being one supposed to have been grown from wild-collected seed gathered in North Carolina(!).

  13. elizabeth a airhart

    growing up north in the usa looking for blue spruce trees
    come christmas was a lovely outing and wreaths for the front door
    when the sky turns different colors as on the astronomy day site
    today a breahtakeing post today does this not change the colors
    of plants and trees in some way – both sites are a must today

  14. Laura

    As a huge fan of Selaginella, I’d like to see a photo of species willldenowii. Please, NOT a fern! Thanks, Laura

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