The Night-Blowing (Blooming) Cereus, which Linnæus dubbed Cactus grandiflorus, now called Selenicereus grandiflorus, begins the fourth and final canto of Darwin’s poem, The Botanic Garden (1791). It provides a fitting transition from the previous third canto, which depicted sorrow and fear through plants that are spooky, stinging, parasitic, and intoxicating. (Darwin, perhaps embarrassed after a drunken naked rant, strongly advocated abstinence from alcohol, consequently chiding the vintner for “converting perfectly good food into poison”).

He also describes plants that are perfectly poisonous on their own, without any need of the vintner’s intervention. One plant he mentions is the Upas Poison-Tree from Java. His depiction of it is so jarring that it inspired the British painter Francis Danby to compose a work based on it. Darwin’s incredible description is contained in the footnote to this plant’s verse. He recounts that criminals on the island of Java are sent to the tree to retrieve its juice, which was used to make poison arrows. If they returned, they were pardoned. But only 1 in 4 returned. Darwin continues, “Not only animals of all kinds, both quadrupeds, fish, and birds, but all kinds of vegetables also are destroyed by the effluvia of the noxious tree; so that, in a district of 12 to 14 miles round it, the face of the earth is quite barren and rocky, intermixed only with the skeletons of men and animals; affording a sense of melancholy beyond what poets have described or painters delineated” (p. 110n). Perhaps accepting the challenge posed in Darwin’s final line, Danby depicts this very scene—a barren, uncanny land, in which two criminals approach the tree. Seemingly, only one will escape its noxious effluvia.

Darwin’s third terrifying canto begins with Circaea or Enchanter’s Nightshade, a plant used, as its name implies, in witchcraft, and often found growing on the “mouldering bones” beneath fresh graves. Whereas this plant’s macabre habitat brings the reader into the darkness of night, the Night-Blowing Cereus provides a light to lead her out of it, for this plant has the peculiar quality of blooming at night—and only at night.

Since the previous day, the flower has laid in preparation. Then, it begins opening on a July evening, around 7 or 8 o’clock, and reaches its peak bloom at midnight. Hence, in Robert John Thornton’s illustration of the cactus (pictured above), the artist has included a clock in the background whose hands read just past midnight. Thornton commissioned additional versions of this illustration. For example, in another edition (also pictured on this page), although still striking, much of what made the above one so remarkable is omitted. The moon no longer peeks out from behind the branches, the building no longer bears the large gilded clock showing the time, and a menacing creature no longer perches near the turret. A still additional version of the illustration serves as the frontispiece to Thornton’s Juvenile Botany, in which a father and son discuss botany (1818).

The Cactus grandiflorus is worthy of attention for the fact that it blossoms at night. These blooms are also notable because, as the name implies, they are quite large, nearly a foot in diameter. In the eighteenth century, this species was thought to possess the largest flower of all the cacti, hence receiving the name, grandiflorus or “large flower.” However, it is now recognized that the blossom size of the species is relatively modest. Nevertheless, the beauty of this flower is not diminished in the least. Quite the contrary, for once it does bloom, the cactus emits a fragrance that perfumes the air with a heady fragrance, redolent of vanilla.

Darwin notes that botanists have not yet explained why the cactus blooms at night, yet he proposes that the plant, just like some animals, could be nocturnal, resting during the day and thus avoiding the heat of the sun. The famous German naturalist, Johann Friedrich Blumenbach, draws the same analogy, arguing that plants like the Night-Blowing Cereus sleep during the day in order to recover their energy, just as some animals. For Darwin and Blumenbach as well as many other eighteenth-century botanists, this hypothesis follows from a much more widely discussed and observed phenomenon: many plants sleep at night. Recently, European researchers confirmed this activity, or lack thereof, in trees. They employed laser scanners to measure the droop of branches and leaves at night: trees of around 5 meters in height drooped around 10 cm at night and then returned to their original position in the morning. Research on the mechanisms responsible for this day-night rhythm, which likely include changes in turgor caused by the presence and absence of light, are ongoing. For more on how Darwin and others understood the sleep of plants, see the exhibition note for Mimosa pudica.

Even if we granted Darwin and Blumenbach’s hypotheses, they do not explain too much, for we are left asking why some plants are nocturnal or “noctiflora,” while others are not. We are still left with the nagging question of why the Selenicereus grandiflorus blooms at night. The answer to this question is not one that would have been readily understood in Darwin’s time because botanists were only beginning to understand the specific relationships that exist between flowers and their pollinators. Yet, in his Juvenile Botany, Thornton hits on this very idea:

Son.—I have seen some butterflies, which like bats, only fly at night.

Father.—These are called Moths, whose bodies resemble butter more than the butterfly, and there are flowers, which open at night, to furnish them with food, as the Evening Primrose (Aenothera), and the Night-blowing Cereus (Cactus Grandiflora).

Thornton was, in fact, precisely right, for it is now recognized that this cactus blooms at night because of its relationship with its pollinators, which must also be nocturnal, that is, bats and moths. In addition to its sweet scent, the opalescent white petals of the Night-Blooming Cereus reflect moonlight that directs these pollinators toward the flower. Whether these bats and moths are so smitten with these blooms that they hold viewing parties in their honor is still yet to be known.