Malvaceae

Malvaceae, the hibiscus, or mallow, family (order Malvales) containing some 243 genera and at least 4,225 species of herbs, shrubs, and trees. Representatives occur in all except the coldest parts of the world but are most numerous in the tropics. A number of species are economically important, including cotton (various Gossypium species), cacao (Theobroma cacao), linden (Tilia species), durian (Durio species), Hibiscus, and okra (Abelmoschus esculentus). See also list of plants in the family Malvaceae.

Taxonomy

Genera now included in Malvaceae were long thought to be very closely related, but, until DNA studies were done at the end of the 20th century, they were placed in four different families: Malvaceae, Bombacaceae, Tiliaceae, and Sterculiaceae, that group of families alone constituting Malvales for some earlier botanists. DNA evidence has shown that many of the genera in those families form evolutionary lineages, leading the 2009 Angiosperm Phylogeny Group (APG III) to include them in a larger single family rather than maintain artificial lineages (ones that do not share a common ancestor).

Physical characteristics

Members of the family are usually readily recognizable even when sterile by their combination of fibrous bark, alternate leaves with toothed margins and stipules (leaflike appendages at the base of the leaf stalk), more or less palmate venation, and multicellular hairs that are stellate to scaly. The base of the flower is often supported by an epicalyx, the outer series of what appears to be a double calyx, and is formed from the bracts or floral leaves of a reduced inflorescence. The sepals meet each other at the edges and are often fused at the base, and closely packed hairs at the base inside secrete nectar. When the nectary is on the inside of the calyx, it probably ensures that the corolla is fused at most only basally. Pollinators—birds and long-tongued insects are common—reach the nectar held in the calyx cup by probing between the bases of the corolla. The edges of the petals overlap regularly. The stamens are often numerous and variously fused or in bundles. The inside wall of the fruit and the surface of the seed are often hairy.

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Plants: From Cute to Carnivorous

Major genera and species

Hibiscus (about 550 species), Pavonia (some 200 species), and Sida (150–200 species) are all widely distributed, Sida being particularly diverse in the New World. Nototriche (about 100 species) is native to South America. An epicalyx (whorl of leaflike bracts that surrounds the sepals) is particularly common among those genera, and the stamens are typically fused into a tube. They are temperate to tropical plants, often herbs or shrubs, with spiny pollen.

Hairs from the ovary wall from genera such as Bombax (about 20 species) and Ceiba (some 11 species) yield the fiber kapok. Ochroma is the source of balsa wood. Several genera, including the Old World baobabs (Adansonia), are cultivated for their flowers and the distinctive appearance of the trees. Members of those genera are typically stout trees with thin, often green bark, and several have stout spines. The leaves are frequently palmately compound.

Grewia (about 290 species) is mostly Neotropical. Microcos (nearly 60 species), Corchorus (40–100 species), and Triumfetta (about 150 species) are pantropical. Two Corchorus species are used as a source of jute fiber. The African hemp (Sparmannia africana) is native to Africa and Madagascar and is grown as an ornamental houseplant. Byttneria (about 135 species) is pantropical but especially South American. Hermannia (some 100 species) is especially common in Africa. Melochia (55 species) is mainly New World. Ayenia (about 70 species) is found in tropical and warm temperate regions of the New World.

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Theobroma (about 20 species) is native to the Neotropics. The flowers are often very distinctive. The petals of that genus are often broad at the base, then narrowed, and finally with another broader, often dangling portion. There are often fewer than 15 stamens, and the complicated flowers are pollinated by small flies and midges that are attracted in part by the dangling petals. Cacao (T. cacao) is the main source of cocoa, and the fruits of other species from the Amazonian region yield delicious pulp for juices or sorbets (e.g., T. grandiflorum).

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The pantropical Sterculia (150 species) and the African Cola (125 species) were part of the former family Sterculiaceae, whose members were noted for having separate male and female flowers borne in often quite large and branched inflorescences. Those genera have sepals that are fused; there are no petals; and the stamens and ovary are borne on a stalk. The individual carpels are free. Caffeine-containing seeds of Cola are used in cola drinks.

Tilia (23 species) grows in north temperate regions. Certain Tilia species (known as linden or basswood trees in the United States and as lime trees in England) are often planted along streets for their beautifully scented flowers or grown for their valuable wood. Dombeya (about 225 species) is extremely diverse on Madagascar; it is sometimes cultivated for its flowers. Melhania (60 species) grows in the tropics. Helicteres (40 species) grows from Asia to the New World. The small genus Thespesia contains about 14 species of trees and shrubs, the flowers of which are often similar in appearance to those of Hibiscus. The flor de maga (T. grandiflora) is recognized as the national flower of Puerto Rico.

Durio (27 species) grows from Southeast Asia to western Malesia. The famous durian fruits are obtained from D. zibethinus. The massive spiny fruits are opened to reveal large seeds surrounded by a creamy fleshy covering, or aril. Some people cannot stand the smell or taste of durians, whereas others think they are one of the world’s finest delicacies.