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At the corner of my block there is a small lovely tropical-looking tree covered with candyfloss flowers of princess pink. Since I live in Brooklyn (which occasionally gets very cold), I have been wondering if the tree is a hallucination or some cunning model made of plastic, but it turns out that the tree is a mimosa tree (Albizia julibrissin), aka the Persian silk tree. Like the green parakeets which live in my neighborhood, this little tree is evidently not as tropical as it seems.
A member of the legume family, the small to medium-sized tree has a springy crown which spreads out like an irregular umbrella. Its delicate bipinnate leaves look like fern fronds (or like Mimoseae plants, to which the Persian silk tree is not closely related). The tree has smooth olive colored bark which becomes striped as it ages. It produces dense clusters of down-like pink flowers all summer. These flowers are attractive to bees and hummingbirds. Perhaps the most interesting aspect of the tree 9other than the pretty flowers) is how animated it is—during the evenings or rain storms the leaves close up and the tree takes on a hunched forlorn appearance. When it is sunny and warm it spreads out like a kid on a comfy sofa. Because of this habit the Persians call it “shabkhosb”—the night sleeper. Apparently its Japanese name is similar and the tree has become representative of sleepy summer evenings in Japanese literature and art.
The trees originally came from Asia and are native to a huge swath of the world from Persia to China. In the past two centuries people planted Albizia julibrissin trees everywhere as an ornamentals and, you guessed it, the species has become invasive. It can be found growing wild in the United States from Southern New York west to Missouri and south to Texas. I wonder if my neighbors even planted their specimen or whether it just showed up like all of the trees of heaven which live around every American city.
A tea made out of this tree is used in traditional medicine to ward off confusion and dark feelings and indeed a clinical study by Korean physicians found that the methylene chloride fraction of Albizzia julibrissin extract produced an antidepressant-like effect in mice (most likely by affecting 5-HT1A receptors—a neural receptor shared by humans).