PLANTAGINACEAE (plantain family)

Plants annual, biennial, or perennial herbs (shrubs elsewhere). Leaves alternate, opposite, or less commonly whorled, sometimes also or only basal, short- to long-petiolate. Stipules absent (the bases of the pair of leaves at a node often connected by a narrow membrane in Callitriche). Leaf blades unlobed or less commonly lobed, variously shaped, the margins usually scalloped or toothed. Inflorescences terminal or axillary, clusters, racemes, spikes, or panicles, sometimes of solitary flowers; bracts and/or bractlets sometimes subtending the flowers, these sometimes inconspicuous. Flowers perfect or less commonly imperfect (monoecious in Callitriche, occasionally incompletely monoecious in Plantago), hypogynous. Cleistogamous flowers absent (except sometimes in Plantago). Calyces actinomorphic or somewhat zygomorphic (absent in Callitriche), (3)4- or 5-lobed, persistent at fruiting. Corollas actinomorphic (in some Plantago) or slightly to strongly zygomorphic and sometimes bilabiate (absent in Callitriche), variously colored, 4- or 5-lobed, the tube variously short to long, sometimes with a basal nectar spur. Stamens 2 or 4 (1 in Callitriche), the filaments attached in the corolla tube (sometimes near its base), sometimes of 2 lengths, the anthers exserted or not, attached near their midpoints or basally, sometimes appearing U- or V-shaped, variously colored. Staminodes absent or present, then 1, well differentiated from the fertile stamens. Pistil 1 per flower, of 2 fused carpels. Ovary 2-locular, with 1 or 2 to more commonly several to numerous ovules per locule, the placentation axile (occasionally appearing basal in Plantago). Style 1 (2 in Callitriche), often persistent at fruiting, the stigma 1 per style, club-shaped to capitate or occasionally linear, entire or 2-lobed. Fruits capsules, variously dehiscent (indehiscent and separating into 4 achenelike nutlets in Callitriche). Seeds numerous or occasionally reduced to 1 or 2 per locule, mostly minute. About 104 genera, 1,820–1,900 species, nearly worldwide.

Many of the genera now included in the Plantaginaceae formerly were classified as members of the Scrophulariaceae. Molecular studies showed that the traditional circumscription of Scrophulariaceae included many genera that had closer affinities to other plant families than to the relatively few genera related to Scrophulariaceae (as reviewed by Tank et al. [2006]). The family that experienced the biggest generic expansion in the order Lamiales as a result of these studies was the Plantaginaceae (Albach and Chase, 2004; Albach et al., 2005; Oxelman et al., 2005), which sometimes was called Veronicaceae in the molecular literature before the issue of nomenclatural priority was clarified. In addition to genera transferred from the Scrophulariaceae, molecular work resulted in the inclusion of two small families of aquatics in the Plantaginaceae, the Callitrichaceae and the non-Missouri family, Hippuridaceae. The resultant expanded circumscription of Plantaginaceae thus includes plants with a variety of pollination syndromes (wind, water, insects, birds) and a related suite of adaptations in floral morphology. For further discussion of the break-up of the former Scrophulariaceae, see the treatment of that family.

As currently circumscribed, Plantaginaceae contains a number of horticulturally important genera, including Angelonia Bonpl. (angelonia, summer snapdragon), Antirrhinum (snapdragon), Chelone (turtlehead), Collinsia (blue-eyed Mary), Digitalis L. (foxglove), Linaria (butter and eggs), Penstemon (beard-tongue), Russelia Jacq. (firecracker plant), Veronica (speedwell), and Veronicastrum (culver’s root). Conversely, some of the genera, including Kickxia, Plantago, and Veronica contain species that are weeds of crop fields and pastures or invasive in rangelands and native plant communities. Several genera have been used medicinally. The Old World genus Digitalis is a rich source of cardiac glycosides, such as digoxin, which can be potent toxins but in proper dosage form the basis for important medications to control the heartbeat.