At this time of year, our eyes are immediately drawn to the brilliant orange, red and yellow pigments of Sugar Maple (Acer saccharum) leaves. However, there’s much to be said about the less flamboyant splashes of color adorning some of the species of trees that provide New England’s spectacular fall foliage. One such subtley-colored fall tree that often grows in upland forests along with Sugar Maples is White Ash (Fraxinus americana). One of the first trees to change color in autumn, White Ash can turn shades of yellow, orange and red, but deep red, maroon and purple are typically the grand finale of this species. Often its leaves progress from green to yellow and eventually maroon. While it might not be the first tree that catches your eye, make a point of looking for its colorful, compound leaves – you won’t be disappointed.
Despite their name, Green Frogs are not always green. They can be brown or tan, as well as many shades of green. Usually Green Frogs in the Northeast are a combination of these colors, but occasionally one sees greenish-blue coloring on a Green Frog. An understanding of what causes a frog’s green color sheds light on why sometimes all or part of a Green Frog may be close to turquoise than green.
Basically there are three types of pigment cells (chromatophores) which stack up on top of each other in a frog’s skin. The bottom layer (melanophores) of pigment cells contain melanin, a pigment that appears dark brown or black. On top of these cells are iridopores, which reflect light off the surface of crystals inside the cells. When light hits these cells, they produce a silvery iridescent reflection in frogs, as well as other amphibians, fish and invertebrates. In most green frogs, sunlight penetrates through the skin to the little mirrors in the iridophores. The light that reflects back is blue. The blue light travels up to the top layer of cells called xanthophores, which often contain yellowish pigments. The light that filters through the top cells appears green to the human eye.
The pictured turquoise-headed Green Frog most likely lacks some xanthophores in the skin on its head, and thus we see reflected blue light there.