Trees with green bark can be quite striking, setting them apart from the more common brown or gray trunks. This distinctive characteristic is uncommon, making these trees intriguing. Understanding why certain trees exhibit this vibrant coloration and identifying these species reveals unique adaptations.
The Science Behind Green Bark
The green coloration in tree bark is primarily due to chlorophyll, the pigment that gives leaves their green hue. Unlike most trees where photosynthesis occurs in leaves, some species have chloroplasts within their bark cells. This allows them to produce energy directly through their trunks and stems. This process, known as bark photosynthesis, is particularly evident in younger stems and thin-barked trees.
Bark photosynthesis offers a significant advantage, especially when leaves are absent, such as in winter for deciduous trees or during drought for desert species. This auxiliary food production provides an energy boost, helping trees survive harsh environments or recover from stresses like defoliation or fire. It contributes to the tree’s carbon gain and supports growth, even when primary photosynthetic organs are not active.
Trees with Distinctive Green Bark
Several tree species are known for their green bark, each with unique features.
Palo Verde
The Palo Verde (Parkinsonia genus), whose name means “green stick” in Spanish, is a prominent example. Native to Southwestern U.S. deserts, these trees have vibrant green bark that actively photosynthesizes. This crucial adaptation helps them thrive in arid conditions by shedding small leaves during drought to conserve water. The Blue Palo Verde (Parkinsonia florida) typically displays bluish-green bark, while the Foothill Palo Verde (Parkinsonia microphylla) tends to have yellowish-green bark.
Quaking Aspen
The Quaking Aspen (Populus tremuloides) is renowned for its green bark, particularly on younger growth. Its smooth bark often appears greenish-white to gray-white, with the green tint from chlorophyll. This bark photosynthesis allows aspens to produce sugars even in winter, providing a food source for wildlife. As aspens age, their bark can become rougher and fissured, sometimes developing black scars from self-pruned branches.
Striped Maple
The Striped Maple (Acer pensylvanicum) is identified by its smooth, green or greenish-brown bark with long, pale, vertical stripes, earning it the name “snakebark maple.” These stripes are most prominent on younger stems and branches, though they may fade or turn reddish-brown as the tree matures. As an understory tree native to North America, its green bark contributes to photosynthesis even in shaded environments before leaves fully emerge in spring.
Corkscrew Willow
The Corkscrew Willow (Salix matsudana ‘Tortuosa’) features smooth, greenish bark, notably on its twisted and contorted branches. This ornamental tree, native to China and Korea, is prized for its curly growth habit, which provides year-round visual interest. Its green bark, combined with its distinctive form, makes it a popular choice in landscaping and floral arrangements.
American Sycamore
The American Sycamore (Platanus occidentalis) often reveals green patches on its trunk. Its outer bark peels away in irregular plates, exposing lighter, often greenish, cream, or white inner bark. This mottled appearance is a hallmark of the sycamore, making it recognizable. While the trunk may not be uniformly green, the exposed patches provide a vibrant contrast.
Tips for Identification
Identifying trees with green bark requires observation, as superficial coverings like moss or algae can also give bark a green appearance. To distinguish true green bark, examine its texture; genuine green bark is smooth, thin, and the color is inherent to the bark tissue, not a surface growth. Moss and algae often appear patchy, fuzzy, or slimy, and can be scraped off.
Beyond bark coloration, tree identification involves looking at multiple features. Consider the tree’s overall shape and size, whether it grows as a single trunk or a multi-stemmed shrub, and its habitat. Observe the leaves, noting their shape, size, margins, and arrangement (opposite or alternate). Flowers, fruits, and even the smell of the bark can provide further clues. In winter, when leaves are absent, studying twigs, leaf buds, and bark patterns is useful for identification.