Flora of North America species comparison

A small spur sometimes is present on the abaxial side of the petiole at the juncture with the stem, to which the specific epithet refers. It is not a spine and occasionally is absent.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Genera ca. 240, species ca. 4350 (52 genera, 250 species in the flora).

Malvaceae comprise taxa traditionally separated among four families: Malvaceae, Bombacaceae Kunth, Sterculiaceae Ventenat, and Tiliaceae Jussieu. Morphological characters distinguishing these previously recognized families are notoriously ambiguous and/or absent. Multiple tribes and genera (for example, Fremontodendron) have been transferred between families as taxonomic boundaries changed throughout history. Molecular phylogenies indicate that only one of the four previously recognized families (Malvaceae in the narrow sense) forms a monophyletic group (C. Bayer et al. 1999; W. S. Alverson et al. 1999) and the monophyly of an expanded familial circumscription, including all four previously accepted families, is well documented (W. S. Judd and S. R. Manchester 1997; Alverson et al. 1998; Bayer et al.). Based on morphological, molecular, and biogeographic data, Malvaceae now include nine subfamilies (Bayer et al.; Alverson et al. 1999), six of which are represented in the flora area; Malvoideae and Bombacoideae form a monophyletic group that is part of a larger clade that includes some

traditional components of Tiliaceae and Sterculiaceae (now Tilioideae and Sterculioideae). A second clade contains Grewioideae and Byttneriodeae. Not included in the flora are members of subfamilies Brownlowioideae Burret, Dombeyoideae Beilschmied, and Helicteroideae Meisner.

Malvaceae range widely in inflorescence structure; all members share a basic repeating bicolor unit (a terminal flower and three bracts or an epicalyx; C. Bayer 1999). Floral nectaries in the family are composed of dense multicellular, glandular hairs on sepals, petals, or androgynophore (S. Vogel 2000). These nectaries provide nectar to a broad range of cells in wood; M. M. Chattaway 1933) are restricted to Malvaceae but are not present in every taxon.

Representatives of Malvaceae are present on every continent except Antarctica; diversity increases in warmer regions. A majority of the genera in Malvoideae and Bombacoideae are native to the New World (P. A. Fryxell 1997); members of Byttnerioideae, Grewioideae, and Sterculioideae are more evenly distributed throughout the Tropics. Tilioideae are restricted to the Northern Hemisphere (C. Bayer and K. Kubitzki 2003).

Malvaceae have an extensive pollen fossil record and a majority of the subfamilies are represented in the Paleocene or Eocene. Tilia (Tilioideae) fossil pollen and leaves are present in western North American temperate forests (where it is now absent) from the mid Eocene (S. R. Manchester 1994; H. W. Meyer and Manchester 1997). North American fossil pollen deposits of Bombacoideae are plentiful in the Cretaceous (W. Krutzsch 1989; B. E. Pfeil et al. 2002 and references therein).

The hairy seed coat of cotton [Gossypium (Malvoideae)] is the most economically valuable product in the family and the historical and evolutionary importance of its domestication is well documented. The seeds of cacao [Theobroma cacao (Sterculioideae)] are the basis of chocolate. Okra [Abelmoschus esculentus (Malvoideae)] is a major vegetable crop in the southeastern United States. Tilia (Tilioideae) trees are planted throughout temperate regions to beautify streets and parks. The marshmallow, Althaea officinalis (Malvoideae), is a perennial herb found in northeastern North America and Europe; the mucilage from its roots was used to make the original marshmallow.

Key to Subfamilies of Malvaceae

(Discussion copyrighted by Flora of North America; reprinted with permission.)