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Malvaceae, Cistaceae, and Muntingiaceae
Malvaceae consists of 243 genera and at least 4,225 species, which are largely tropical but include some plants from temperate regions. The largest or most important genera in the family include Hibiscus (550 species), Dombeya (225 species), Sida (200 species), Pavonia (150 species), Sterculia (150 species), Malva (56 species), and Gossypium (40 species, including cotton plants). Malvaceae now includes several formerly segregate families, mostly woody, with members such as Theobroma (cocoa, or chocolate), Ceiba (kapok), and Ochroma (balsa). Members of the family are usually readily recognizable even when sterile by their combination of fibrous bark, alternate stipulate leaves with toothed margins (the stipules are not sheathing), more or less palmate venation, and multicellular hairs that are stellate to scaly. An epicalyx, the outer series of what appears to be a double calyx, is common 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.
Cistaceae, or the rock rose family, contains 8 genera and 175 species, which are commonly found in temperate or warm temperate areas, especially the Mediterranean region. Among the major genera in the family, Helianthemum (80–110 species) grows from Europe and North Africa to Central Asia and in the Americas; Cistus (18 species) grows around the Mediterranean and on the Canary Islands; and Lechea (17 species) is native to the New World. Members of Cistaceae are aromatic shrubs, often with opposite leaves that are more or less joined by their broad bases. The inner three sepals are much larger than the two outer sepals. The free petals are crumpled when in bud, and there are numerous stamens. The seed coat is often gelatinous, the endosperm starchy, and the embryo more or less strongly curved, which is an odd combination of characters. Many shrubby species of Cistus have been introduced into North American gardens. C. ladanifer and other species yield pleasantly scented resins that are used in soaps and as scented additives to other products. Helianthemum species, which are all commonly called sun rose, are also occasionally planted by horticulturists.
Muntingiaceae is a small family of three genera and three species from the Neotropics. The family’s leaves are two-ranked, often unequal at the base, and with structures that look like stipules but are in fact the first leaves of the axillary shoot. The flowers are in small groups just above the leaf axil; the sepals meet edge on; the petals are shortly narrowed at the base and are crumpled in bud; and the stamens are numerous. The ovary is very variable, and the fruit is a berry. The Neotropical Muntingia calabura (calabura, jam tree, or Jamaican cherry) is fast-growing and can be used as a firewood crop.
Cochlospermaceae (with genera Cochlospermum and Amoreuxia) and Diegodendraceae (with genus Diegodendron) are former families that are now included in Bixaceae (which used to include only one genus, Bixa). The plants in Bixaceae have fibrous bark, canals containing exudate, branches that end at the inflorescence, large flowers, and seed coats with a very distinctive anatomy.
Bixa contains five species of trees and shrubs from the Neotropics. They have scalelike hairs, leaves with palmate venation, and stipules ensheathing the bud; there is red or orange exudate. The large flowers have anthers that disperse pollen through terminal pores. The ovules are borne on the walls of the ovary; the capsule is spiny; and the seeds have a pulpy coat. The pulp around the seeds of B. orellana yields annatto, a red dye used for both foods and body paint. The species has been planted throughout the tropics.
Cochlospermum (12 species), found throughout the tropics, and Amoreuxia (3 species), restricted to the southwestern United States and Central America, consist of herbs with stout roots to trees. The leaves in these genera are spirally arranged and palmately lobed, with narrow stipules. The flowers are large and usually yellow, and there are many stamens whose pollen sacs open by pores. The capsule wall separates into two layers and opens down the partitions to release the numerous hairy curved seeds. The plants often have a yellowish resinous exudate.
Diegodendron consists of a single species, D. humbertii, which is an evergreen tree that grows on Madagascar. The leaves are borne in two ranks on the stem and have pellucid dots; the stipules are large and encircle the stem. The style comes from the bottom of the ovary, and the fruit is spiny, the single large seed having a sticky coat.
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