The circumscription of the Malvaceae is controversial. The traditional Malvaceaesensu stricto comprise a very homogeneous and cladisticallymonophyletic group. Another major circumscription, Malvaceaesensu lato, has been more recently defined on the basis that genetics studies have shown the commonly recognised familiesBombacaceae,Tiliaceae, andSterculiaceae, which have always been considered closely allied to Malvaceaes.s., are not monophyletic groups. 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.
This article is based on the second circumscription, as presented by theAngiosperm Phylogeny Website.[5] The Malvaceaes.l. (hereafter simply "Malvaceae") comprise nine subfamilies. A tentativecladogram of the family is shown below. The diamond denotes a poorly supported branching (<80%).
Until recently, relationships between these subfamilies were either poorly supported or almost completely obscure. Continuing disagreements focused primarily on the correct circumscription of these subfamilies, including the preservation of the family Bombacaceae.[13] A study published in 2021 presented a fully resolved phylogenetic framework for Malvaceaes.l. using genomic data for all nine subfamilies.[14]
Regarding the traditional Malvaceaes.s., the subfamilyMalvoideae approximately corresponds to that group.
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 withmucilage canals, and stratified wedge-shaped phloem.[16] These affinities were problematic because they were not always shared within the core families.[17] Later studies revealed more unambiguous synapomorphies within Malvaceaes.l.. Synapomorphies identified within Malvaceaes.l. include the presence of tile cells, trichomatous nectaries, and aninflorescence structure called a bicolor unit.[18] Tile cells consist of vertically positioned cells interspersed between and dimensionally similar to procumbent ray cells. Evidence of Malvean wood fossils has confirmed their evolutionary link in Malvaceaes.l., as well as explained their diverse structures.[19] Flowers of Malvaceaes.l. exhibit nectaries consisting of densely arranged multicellular hairs resembling trichomes. In most of Malvaceaes.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.[20] Malvean flowers also share a unifying structure known as a bicolor unit, named for its initial discovery in the flowers ofTheobroma 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 thepeduncle 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 characteristic.[21]
The English common name 'mallow' (also applied to other members of Malvaceae) comes from Latinmalva (also the source for the English word "mauve").Malva itself was ultimately derived from the word for the plant in ancient Mediterranean languages.[22]Cognates of the word includeAncient Greekμαλάχη (malákhē) orμολόχη (molókhē),Modern Greekμολόχα (molókha), modernArabic:ملوخية (mulukhiyah) and modernHebrew:מלוחיה (molokhia).[22][23]
Stellate hairs on the underside of a dried leaf ofMalva alcea
Leaves are generallyalternate, often palmately lobed or compound and palmately veined. The margin may be entire, but whendentate, a vein ends at the tip of each tooth (malvoid teeth). Stipules are present. Thestems contain mucous canals and often also mucous cavities. Hairs are common, and are most typicallystellate.[citation needed] Stems of Bombacoideae are often covered in thick prickles.[24]
The flowers are commonly borne in definite or indefinite axillaryinflorescences, which are often reduced to a single flower, but may also becauliflorous, oppositifolious, or terminal. They often bear supernumerarybracts in the structure of a bicolor unit.[21] They can be unisexual or bisexual, and are generallyactinomorphic, often associated with conspicuous bracts, forming anepicalyx. They generally have five valvatesepals, most frequently basallyconnate, with five imbricatepetals. Thestamens are five to numerous, and connate at least at their bases, but often forming a tube around thepistils. The pistils are composed of two to many connatecarpels. Theovary is superior, with axial placentation, with capitate or lobed stigma. The flowers havenectaries made of many tightly packed glandularhairs, usually positioned on the sepals.[20]
^Heywood, Vernon Hilton; Brummitt, R. K.; Culham, A.; Seberg, O. (2007).Flowering Plant Families of the World. Richmond Hill, Ontario, Canada: Firefly Books.ISBN9781554072064.
Baum, D. A.; W. S. Alverson; R. Nyffeler (1998). "A durian by any other name: taxonomy and nomenclature of the core Malvales".Harvard Papers in Botany.3:315–330.
Bayer, C. and K. Kubitzki 2003. Malvaceae, pp. 225–311. In K. Kubitzki (ed.),The Families and Genera of Vascular Plants, vol. 5, Malvales, Capparales and non-betalain Caryophyllales.
