Malvaceae, or the mallows, is a family of flowering plants estimated to contain 244 genera with 4225 known species. Well-known members of economic importance include okra, cotton, cacao and durian. There are also some genera containing familiar ornamentals, such as Alcea, Malva and Lavatera, as well as Tilia. The largest genera in terms of number of species include Hibiscus, Sterculia, Dombeya, Pavonia and Sida.
Taxonomy and nomenclature
The circumscription of the Malvaceae is controversial. The traditional Malvaceae sensu stricto comprise a very homogeneous and cladistically monophyletic group. Another major circumscription, Malvaceae sensu lato, has been more recently defined on the basis that molecular techniques have shown the commonly recognised families Bombacaceae, Tiliaceae, and Sterculiaceae, which have always been considered closely allied to Malvaceae s.s., are not monophyletic groups. Thus, the Malvaceae can be expanded to include all of these families so as to compose a monophyletic group. Adopting this circumscription, the Malvaceae incorporate a much larger number of genera.
Subfamilies
This article is based on the second circumscription, as presented by the Angiosperm Phylogeny Website. The Malvaceae s.l. comprise nine subfamilies. A tentative cladogram of the family is shown below. The diamond denotes a poorly supported branching. It is important to point out the relationships between these subfamilies are still either poorly supported or almost completely obscure. There are continuing disagreements over the correct circumscription of these subfamilies, including the preservation of the family, Bombacaceae. The circumscription of the family may change dramatically as new studies are published. If looking for information about the traditional Malvaceae s.s., we recommend referring to Malvoideae, the subfamily that approximately corresponds to that group.
Synapomorphies
The relationships between the "core Malvales" families used to be defined on the basis of shared "malvean affinities". These included the presence of malvoid teeth, stems with mucilage canals, and stratified wedge-shaped phloem. These affinities were problematic because they were not always shared within the core families. Later studies revealed more unambiguous synapomorphies within Malvaceae s.l.. Synapomorphies identified within Malvaceae s.l. include the presence of tile cells, trichomatous nectaries, and an inflorescence structure called a bicolor unit. Tile cells consist of vertically positioned cells interspersed between and dimensionally similar to procumbent ray cells. Evidence of Malvean wood fossils have confirmed their evolutionary link in Malvaceae s.l., as well explained their diverse structures. Flowers of Malvaceae s.l. exhibit nectaries consisting of densely arranged multicellular hairs resembling trichomes. In most of Malvaceae s.l., these trichomatous nectaries are located on the inner surface of the sepals, but flowers of the subfamily, Tiliodeae, also have present nectaries on the petals. Malvean flowers also share a unifying structure known as a bicolor unit, named for its initial discovery in the flowers of Theobroma bicolor. The bicolor unit consists of an ordered inflorescence with determinate cymose structures. The inflorescence can branch off the main axis, creating separate orders of the flowers, with the main axis developing first. Bracts on the peduncle subtend axillary buds that become these lateral stalks. One bract within this whorl is a sterile bract. The bicolor unit is a variable structure in complexity, but the presence of fertile and sterile bracts is a salient character.
Names
The English common name 'mallow' comes from Latin . Malva itself was ultimately derived from the word for the plant in ancient Mediterranean languages. Cognates of the word include Ancient Greek μαλάχη or μολόχη, Modern Greek μολόχα, modern ملوخية and modern מלוחיה.
Description
Most species are herbs or shrubs, but some are trees and lianas.
Leaves and stems
are generally alternate, often palmately lobed or compound and palmately veined. The margin may be entire, but when dentate, a vein ends at the tip of each tooth. Stipules are present. The stems contain mucous canals and often also mucous cavities. Hairs are common, and are most typically. Stems of Bombacoideae are often covered in thick prickles.
Flowers
The flowers are commonly borne in definite or indefinite axillary inflorescences, which are often reduced to a single flower, but may also be cauliflorous, oppositifolious, or terminal. They often bear supernumerary bracts in the structure of a bicolor unit. They can be unisexual or bisexual, and are generally actinomorphic, often associated with conspicuous bracts, forming an epicalyx. They generally have five valvate sepals, most frequently basally connate, with five imbricate petals. The stamens are five to numerous, and connate at least at their bases, but often forming a tube around the pistils. The pistils are composed of two to many connate carpels. The ovary is superior, with axial placentation, with capitate or lobed stigma. The flowers have nectaries made of many tightly packed glandular hairs, usually positioned on the sepals.
Fruits
The fruits are most often loculicidal capsules, schizocarps or nuts.
A number of species are pests in agriculture, including Abutilon theophrasti and Modiola caroliniana, and others that are garden escapes. Cotton, kenaf, cacao, kola nut, and okra are important agricultural crops. The fruit and leaves of baobabs are edible, as is the fruit of the durian. A number of species, including Hibiscus syriacus, Hibiscus rosa-sinensis and Alcea rosea are garden plants.
