Brilliant Green: The Surprising History and Science of Plant Intelligence by Stefano Mancuso and Alessandra Viola (review)

Plants comprise over 99% of the biomass of the earth, and without them there would be no animal life on the planet. Moreover, the thriving of trees and other plants will be necessary for life on earth to survive, and continue to cope with, the negative consequences of human-induced climate change. The importance of plants is not just biological. Imagine the impoverishment of life in great cities like London, Paris, and New York without the green spaces and flowers of Hyde Park, the Tuileries Garden, and Central Park.

Metropolitan Washington, DC—my home environment—is graced by the presence of Rock Creek Park, an expansive woodland resource in the center of the city. In the first spring of my retirement, I have been walking the trails adjacent to the creek, admiring and transported by the profusion and beauty of plant life. A recent sojourn in the park brought to mind Wordsworth’s “Tintern Abbey” (1798), in which he relates that he is

A lover of the meadows and the woods,And mountains; and of all that we beholdFrom this green earth;

        … well pleased to recognizeIn nature and the language of the sense,The anchor of my purest thoughts, the nurse,The guide, the guardian of my heart, and soul. …

(ll. 105–12)

Wordsworth here and elsewhere suggests a spiritual connection between the plant world and the human psyche. In his famous poem about encountering daffodils “dancing in the breeze,” he exclaims that “A poet could not but be gay, / In such a jocund company” (“I wandered lonely as a cloud” [1815], ll. 6, 15–16). Indeed, the memory of the daffodils fills his heart with pleasure when at later times, “In vacant or in pensive mood,” he thinks of them (l. 20).

One doesn’t have to be a Romantic poet to feel a deep connection with plants. Walking many years ago in a quiet and remote mountainous grove of bristlecone pines, breathing the thin air and experiencing the sight of these ancient dwarfs had an effect on my atheistic self that I wouldn’t hesitate to call spiritual. It would be a sacrilege for someone to willfully damage them. To be sure, some are indifferent to the greenness of the earth; indeed, the existentialist philosopher and writer, Jean-Paul Sartre, according to his companion Simone de Beauvoir, was “allergic to chlorophyll” (Barnes 1959, 391). But this is unusual, and virtually anyone can appreciate what plants have to offer. Readers of Brilliant Green will have that appreciation greatly enhanced.

This short book is written by a professor at the University of Florence and director of the International Laboratory of Plant Neurobiology in Italy (Mancuso), and a science journalist (Viola). The authors pose the central question of their book in the first paragraph: “Are plants intelligent? Do they solve problems and communicate with their surroundings—with other plants, insects, and higher animals? Or are they passive, unfeeling organisms without a trace of individual or social behavior?” (1). In an entertaining and thought-provoking way, they endeavor to answer to this question by making the case for plants being intelligent, and even sentient. They proceed by describing and characterizing the behaviors—including the relationships between plant and animals—that plants rely on for reproduction, defense against predators, and even in some cases for nourishment.

Under the impact of Darwinian biology over the past 150 years, humans have embraced, or at least been forced to recognize, the continuity between their mental abilities and those of animals. The authors demonstrate that when the impressive abilities of plants are contemplated, the many similarities between plants and animals come into view. Plants, of course, are not inert like rocks; they not only grow and reproduce, but they respond to stimuli. Mancuso and Viola relate that “plants use their senses to orient themselves in the world, interacting with other plant organisms, insects, and animals, communicating...