It never gets old. First the larches (Larix) burst out with colorful cones, then comes Douglas fir (Pseudotsuga), the spruces (Picea) and firs (Abies), and finally the pines (Pinus). This year, the spruces and firs have been unbelievable, and right now, these colorful future seed cones are close to their peak visual intensities. The absolute highlight for me last week was stumbling upon a young Himalayan fir from India (Abies pindrow,41-2008*A; left image) in the conifer collection. Just about my height, the top half of the small tree was covered with the most intensely purple cones that I have ever seen.
The curious thing to contemplate is why young seed cones in some conifers have such intense and transient pigmentation (it typically goes away in a matter of a week or two). The pink, red (for example, the Sakhalin spruce, Picea glehnii, 16485*N; lower right) and purple colors are created by a class of pigments called anthocyanins, the very same chemicals that turn many leaves red in the autumn and that can make pink to red to purple colors in flowers. In flowers, these pigments are typically invoked to attract animal pollinators. But, in conifers, all of which are wind-pollinated, these pigments clearly do not serve this role. Morever, some species of conifers produce young seed cones that are green: for example, the Korean fir (Abies koreana, 557-86*C; upper right) and the golden larch (Pseudolarix amabilis).
There appears to be a bit of a correlation between the amount of red pigmentation in young cones and altitude. Populations and species that grow at higher elevations appear to be on the redder side, and those at lower elevations, on the greener side. But, why? Some have hypothesized that the pigmentation may protect the young delicate cones from high levels of UV; others have suggested these pigments may protect the cones from too much light (which can damage the photosynthetic apparatus). I’m not buying this, since these cones are right next to the delicate young leaves which are decidedly not red-pigmented. Others have noted that the red pigmentation can help raise the temperature of the cones (but for what purpose?). In the end, no one really knows. So, get out there and simply enjoy what nature has put on display at the Arnold Arboretum.
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