arum (redirected from aroid)

arum, common name for the Araceae, a plant family mainly composed of species of herbaceous terrestrial and epiphytic plants found in moist to wet habitats of the tropics and subtropics; some are native to temperate zones. The family is characterized by an inflorescence consisting of a single spadix (a fleshy spike bearing small flowers) and a usually showy and flowerlike bract (modified leaf) called a spathe, which surrounds the spadix. The titan arum (Amorphophallus titanum) of Sumatra, which also is grown in a number of botanical gardens, has one of the largest inflorescences of any plant, the spadix reaching a height of 10–15 ft (3–4.6 m) above the ground.

Common Species

Commonly cultivated for their showy inflorescences are the arum lilies, or callas (genus Zantedeschia), native to tropical and S Africa; the common florists' white-spathed calla lily is Z. aethiopica. The wild calla, or water arum (Calla palustris), of E North America and other northern regions is similar to the calla lily but smaller and is not usually cultivated.

Several plants of the arum family are grown (often as house plants) for their ornamental foliage, e.g., species of the genera Monstera, Philodendron, and Caladium, all native to the American tropics. Monstera is a vine popular for its perforated and deeply lobed leaves. Philodendron, usually a climbing shrub in the tropics, is now one of the most popular house plants. Caladium, noted for its multicolored foliage, is sometimes mistakenly called elephant's-ear, a name properly applied to taro (Colocasia esculenta) or dasheen.

Taro, with its large, starchy corms or rootstocks (characteristic of the arum family) is a major source of food in the Pacific islands and East Asia; in Hawaii it is the main ingredient of poi. Some 1,000 varieties are now cultivated in many warm regions, including the S United States; as a food plant it is known by many local names.

Plants of the arum family native to the United States are found chiefly in the eastern and central states; all species are bog or aquatic plants except Arisaema, which grows in moist woodlands. The jack-in-the-pulpit, or Indian turnip (A. triphyllum), has a spadix (jack) enveloped by a purplish-striped spathe (the pulpit). Its starchy corms were eaten by the Native Americans, as were those of the tuckahoe or Indian bread, sweet flag (Acorus calamus), and skunk cabbage (Symplocarpus foetidus). The latter two and the jack-in-the-pulpit were sources of medicinal substances. Sweet flag, found in many north temperate regions, yields flavorings and calamus, a perfume oil.

Skunk cabbage, found in both E Asia and E North America, is one of the most abundant and earliest-blooming northern wildflowers. The unpleasant odor noticeable when the plant is bruised is produced by the acrid sap, which contains needle-shaped crystals of calcium oxalate, called raphides, that are formed as a metabolic byproduct. This acridity, characteristic of the arum family, is removed from the corms by cooking.

Classification

The family is classified in the division Magnoliophyta, class Liliopsida, order Arales.