VERBENACEAE (Vervain Family)

Plants annual or perennial herbs (shrubs or trees elsewhere). Stems usually branched, usually strongly 4-angled (square) in cross-section (occasionally 6-angled), often hairy, sometimes bristly or roughened, or some or all of the hairs gland-tipped. Leaves opposite (occasionally some of them whorled), well-developed, petiolate or more commonly sessile, the petiole often winged. Stipules absent. Leaf blades simple, but sometimes deeply lobed, the margins usually toothed, the surfaces usually hairy, the hairs sometimes with pustular bases, sometimes stiff and calcified, some or all of the hairs sometimes gland-tipped. Inflorescences terminal and/or axillary spikes, these occasionally short and headlike, occasionally grouped into terminal panicles, the flowers subtended by persistent bracts. Flowers zygomorphic, often weakly so, hypogynous, perfect; cleistogamous flowers absent. Calyces usually deeply 5-lobed (shallowly lobed elsewhere), the lobes then slightly unequal, in Lippia with only 2(4) incurved, usually shallow, keeled lobes, persistent at fruiting. Corollas 4- or more commonly 5-lobed, funnelform or more or less trumpet-shaped, often with a slender tube that is slightly expanded near the throat, less commonly 2-lipped, the inside of the throat sometimes with a band of hairs, but not appendaged. Stamens 4, the filaments attached in the corolla tube, short, the anthers not exserted, attached at their base, usually yellow, sometimes with a minute, glandular appendage; staminodes absent (staminode 1 elsewhere). Pistil 1 per flower, of 2 fused carpels (but often appearing 4-carpellate), sometimes 1 carpel aborting during development. Ovary often with a basal nectar disc or a very short, stout stalk (gynophore), entire to more commonly deeply 4-lobed, 2- or more commonly 4-locular, with 1 ovule per locule, the placentation basal. Style 1, usually not persistent at fruiting, situated at the tip of the ovary, not exserted, appearing broadly notched or with a pair of very short, unequal, triangular branches at the slightly expanded and often somewhat flattened tip, the stigma consisting of a swollen glandular area, usually along only 1 of the style branches (in Lippia, the branches very short and inconspicuous, the stigmatic region appearing terminal and more or less capitate). Fruits usually schizocarps splitting (sometimes tardily so) into (1)2 or 4 nutlets, these 1-seeded, indehiscent, with a hardened sometimes bony outer wall (drupes with 1, 2, or 4 stones elsewhere). About 35 genera, about 1,000 species, nearly worldwide, most diverse in tropical and warm-temperate regions.

In recent decades phylogenetic analyses based on both morphological (Cantino 1992a, 1992b; Judd et al., 1994, 2008) and molecular (Wagstaff and Olmstead, 1997; Marx et al., 2010) data sets has clarified the familial limits of the closely related families, Verbenaceae and Lamiaceae. Interestingly, the revised classification is similar to one first suggested more than 75 years ago (Junell, 1934). Traditionally, the two families were distinguished morphologically mainly based on the position of the style relative to the ovary: toward the ovary base in a deep central depression in Lamiaceae vs. at the tip of the ovary in Verbenaceae. This character has since been reinterpreted as a specialization within a more broadly circumscribed Lamiaceae. Separation of the two families now rests on variation of a series of subtle characters, including indeterminate vs. determinate inflorescence axes, differences in the attachment patterns of the ovules, ultrastructure of the pollen grains, and production of more or less discrete (often more or less globose), well-developed, stigmatic regions on 1 or both of the 2 stylar lobes in Verbenaceae vs. indistinct receptive areas near the tips of the style branches in Lamiaceae.

The result of this reclassification has been a considerable reduction in the size of the Verbenaceae, from the traditional view of about 100 genera and more than 2,600 species to only about 35 remaining genera with about 1,000 species. For Missouri, the effects of the changes have been relatively modest: the two woody genera, Callicarpa and Vitex, have been transferred to the Lamiaceae in the present treatment.

Several genera of Verbenaceae contain species that are cultivated as garden ornamentals or house plants. Some of the subtropical and tropical groups, such as Lantana L., are frost-tender perennials that are grown as annuals in Missouri. The wood of some tropical tree species of Citharexylum L. (fiddlewood) is prized for use in cabinetry, inlays, and musical instruments. Aloysia citriodora Paláu (lemon verbena) is used in herbal teas, as a flavoring, and as an ingredient in sachets and potpourri. Some South American species of Lippia have been used as spices as a substitute for oregano. Various species have purported medicinal properties.