Excerpt From Book
Blue is not a common color in plant organs other than flowers. Our view of the world would be quite different if a segment of deciduous plants had brilliant blue-colored leaves included with the reds and yellows that dominate fall. Red as a fall color is the result of unmasking and intensifying anthocyanins as chlorophyll breaks down in the leaf. Since blue is one manifestation of anthocyanin pigments, I am not sure why it is not found in fall colors except that it may be related to the cellular pH in senescing leaves. It suggests that blue as a flower color has advantages for attracting pollinators that warranted its evolution in flowers.
Even so, some types ot plants normally have bluish leaves. They can complement species with blue flowers by repeating their color in the garden. Blue foliage color is more common in certain plant groups than others. It is most common in conifers such as fir (Abies). juniper (Juniperus), cedar (Cedrus), and spruce (Picea); ornamental grasses such as fescue (Festuca) and oatgrass (Helictotricon); and desert species such as Agave, Echeveria, and Euphorbia. It is even found in perennials like hostas and rue (Ruta). The blue coloring is not always due to additional anthocyanin pigmentation in the leaf. Rather, many of these plants have a glaucous bloom made of waxes. This bloom provides a "cloudy window" over the leaf. When seen through this covering layer, the normwal green color of the leaf appears blue. This ecological adaptation helps the leaf to reduce water loss in harsh environments.
Blue color can also appear in fruits. These are not as common and have more subtle appeal than the boisterous claims of red or orange fruits. My favorite choice in this category is the porcelain berry (Ampelopsis brevipedunculata). I first saw this plant trained in a zigzag pattern atop a railing alongside descending steps at Dumbarton Oaks Gardens of Georgetown, Washington, DC. This arrangement was a wonderful way to "tame" this vine to provide close inspection of the multicolored berries that appear in late summer into fall. Other plants with ornamental blue fruit include barberry (Berberis) fringe tree (Chionanthus), Clintonia, Clerodendrum, Juniperus, privet (Ligustrum), Oregon grape (Mahonia), Solomon's seal (Polygonatum), skunk cabbage (Symplocos), Vaccinium, and arrowood (Viburnum).
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