Araceae

• 1. Introduction

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  Araceae is a family of flowering plants whose flowers are never born in the usual way. Instead of petals arranged on a stem, they emerge on a dense, spike-like column called a spadix, most often wrapped in a leaf-like sheath called a spathe. That unusual arrangement is the calling card of about 3,750 known species spread across 114 genera, from tropical rainforests to the shallows of ponds. Their common names read like a catalogue of the strange: titan arum, skunk cabbage, voodoo lily, dumb-cane, and duckweed. What binds them is a set of shared structures and a shared chemistry that can reward or punish anything that gets too close. How does a plant family that includes the smallest flowering plant on Earth also produce the largest unbranched inflorescence in the world? How do these plants heat themselves like warm-blooded animals? And why have they fed millions of people for generations while remaining almost invisible to the global food trade?

• 2. Heat, Smell, and Deception

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  Amorphophallus titanum, the titan arum, can raise its spadix temperature to 45 degrees Celsius, even when the surrounding air is far colder. That ability to generate heat is shared across many members of the arum family, and it serves a precise purpose. Beetles are attracted by warmth; the plant offers heat as a reward in exchange for pollination. In colder climates, the same heat production protects sensitive tissue from frost damage. The eastern skunk-cabbage, Symplocarpus foetidus, is one of the best-known thermogenic aroids in North America, capable of melting through late-winter snow to bloom early. Other thermogenic members include Amorphophallus paeoniifolius, the elephant-foot yam; Helicodiceros muscivorus, the dead-horse arum lily; and Sauromatum venosum, the voodoo lily. The titan arum and the dead-horse arum lily take the strategy a step further by releasing a powerful odor resembling rotten meat. That smell attracts flies rather than beetles, and the heat produced by the plant helps carry the scent outward through the air. Pollination in these plants depends entirely on the animal being fooled, warmed, or rewarded into cooperation.

• 3. A Dangerous Chemistry

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  Calcium oxalate crystals, formed into needle-like structures called raphides, run through the leaves and tissues of nearly every plant in this family. Raw consumption of aroid vegetation can cause edema, vesicle formation, and dysphagia, accompanied by a painful burning sensation in the mouth and throat that can persist for up to two weeks. In smaller exposures, people describe the feeling as sand or glass moving through the esophagus and mouth, a sensation that can last up to 48 hours. In severe cases, anaphylactic shock can cause the throat to swell enough to restrict breathing. Dieffenbachia earned the folk name "dumb-cane" because ingesting it can temporarily rob a person of speech. That nickname, though attached to one genus, could fairly apply to virtually any member of the Araceae. Cooked preparation changes the picture. Genera including Alocasia, Colocasia, and Xanthosoma can be safely consumed once cooked. The ripened fruits of Monstera deliciosa are also edible. The line between food and hazard in this family runs through cooking temperature, not through the plant itself.

• 4. Feeding the World Quietly

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  Colocasia esculenta, known as kochu, taro, or dasheen, feeds millions of people across Asia, the Pacific, and parts of Africa. Xanthosoma, called cocoyam or tannia, plays a similar role in Latin America and West Africa. Amorphophallus paeoniifolius, the elephant-foot yam, and Typhonium trilobatum are also cultivated as food crops. The main product from these plants is the corm, a starchy underground storage organ, though leaves and flowers also find their way into local cooking. The Crop Trust has called the food aroids "orphan crops": little traded on international markets, largely ignored by commercial plant breeders, yet widely grown and essential to subsistence agriculture across the tropics. Monstera deliciosa, now a familiar houseplant in wealthier countries, also produces an edible fruit known as Mexican breadfruit. The global food system has not invested heavily in these plants, but the communities that depend on them have cultivated them for generations.

• 5. Centuries of Classification

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  Theophrastus recorded observations of plants now placed in Araceae in his work Enquiry into Plants, making his notes among the earliest written descriptions of the family. Despite that ancient notice, the Araceae were not recognized as a distinct plant group until the 16th century. In 1789, Antoine Laurent de Jussieu sorted all climbing aroids into a genus he called Pothos, while placing terrestrial aroids into either Arum or Dracontium in his book Familles des Plantes. The first major formal classification came from Heinrich Wilhelm Schott, whose Genera Aroidearum appeared in 1858 and whose Prodromus Systematis Aroidearum followed in 1860. Schott organized the family around floral characteristics and favored a narrow definition of each genus. Adolf Engler published a rival system in 1876 and refined it steadily through to 1920. Engler anchored his groupings in vegetative characters and anatomy rather than flowers, and the his approach attracted more followers in the years before molecular methods changed the field. A comprehensive taxonomy produced by Mayo and colleagues arrived in 1997. Modern gene-sequence studies confirmed that the Araceae, including duckweeds formerly placed in their own family Lemnaceae, form a single monophyletic group. The APG III system of 2009 folded the Lemnaceae into the Araceae. The 2010 New Flora of the British Isles resisted that merger, keeping Lemnaceae separate, but the 2019 edition incorporated Lemna and its relatives into the family.

• 6. Extremes Within One Family

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  143 genera are currently accepted within the Araceae, and the range of forms they contain is hard to hold in a single picture. Wolffia, a duckweed included in the family after the merger with Lemnaceae, is the smallest flowering plant on Earth and also produces the smallest fruit. The titan arum, Amorphophallus titanum, holds the opposite record: the largest unbranched inflorescence in the world. That plant is sometimes mistakenly described as the world's largest flower, but the inflorescence is a collection of many small flowers arrayed on the spadix, not a single bloom. Philodendron is a keystone genus in neotropical rainforest ecosystems and also a fixture of home interiors worldwide. Anthurium, Epipremnum, Monstera, and Zantedeschia are among the most recognized ornamental genera. The aquatic genera Anubias, Bucephalandra, and Cryptocoryne are prized by aquarium hobbyists. The recently described Lagenandra of India is beginning to draw interest in the aquascaping community. A comprehensive genomic study of the duckweed Spirodela polyrhiza was published in February 2014, continuing work on the family's smallest members even as the titan arum commands attention at the other end of the scale.

• 7. Ancient Roots in Stone

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  The fossil record of the Araceae reaches back to the Early Cretaceous, placing this family among the oldest documented angiosperms. Three notable Early Cretaceous fossils have been identified: Spixiarum kipea, an aroid recovered from the late Aptian of Brazil; Orontiophyllum ferreri, a leaf fossil from the late Albian of Spain; and Turolospadix bogneri, a preserved aroid spadix also from the late Albian of Spain. Those specimens show that the distinctive spadix structure was already in place during a period when dinosaurs still walked the Earth. The family's long fossil history, combined with modern genomic evidence placing the Araceae as the first diverging group within the order Alismatales, suggests a lineage that has been adapting its unusual flower architecture for a very long time. The aquarium plant Cryptocoryne, cultivated today by hobbyists around the world, belongs to the same ancient order.