15. Plantago L. (plantain)

Plants annual, biennial, or perennial herbs (shrubs elsewhere), with taproots or fibrous roots (the roots somewhat fleshy in P. cordata). Aerial stems absent or very short (except in P. indica). Leaves basal and sometimes also alternate (opposite in P. indica), sessile or petiolate. Stipules absent, but the leaf bases sometimes somewhat expanded and sheathing. Leaf blades simple, the margins entire, wavy or toothed, sometimes with slender, rounded pinnate lobes, the venation pattern consisting of a more or less prominent midvein and often a series of only slightly less prominent, more or less parallel, lateral veins (these branching from near the blade base and rejoining the midvein near the blade tip). Inflorescences terminal (axillary in P. indica) spikes, usually elongate (sometimes shorter and somewhat headlike in P. indica), with numerous dense flowers, at least above the basal portion (more open in P. cordata), long-stalked at maturity. Flowers individually inconspicuous, actinomorphic or somewhat zygomorphic, hypogynous, perfect or occasionally incompletely monoecious (with functionally staminate and perfect flowers intermingled), each subtended by a scalelike bract. Cleistogamous flowers sometimes present (noticeable because the anthers and stigmas are not strongly exserted at flowering). Calyces deeply 4-lobed (appearing 3-lobed in P. lanceolata), persistent at fruiting, the 2 lobes adjacent to the bract sometimes fused entirely or to above the midpoint, the other lobes free nearly to the base. Corollas 4-lobed, papery, mostly persistent at fruiting, white to tan or slightly grayish-tinged, the short tube slender, the lobes (or 3 of them) abruptly spreading (except in cleistogamous flowers), overlapping in bud, sometimes slightly differing in shape. Stamens 2 or 4, alternating with the corolla lobes, the filaments attached in the corolla tube, the anthers exserted (except in cleistogamous flowers), often somewhat heart-shaped or horned, attached toward their midpoints (or at least above the base), yellow or occasionally dark purple. Pistil 1 per flower, of 2 fused carpels. Ovary superior, 2-locular, with usually 1 to several ovules per locule, the placentation axile or appearing more or less basal. Style 1, the stigma often 2-lobed, it or its lobes mostly linear to club-shaped. Fruits membranous capsules (achenes elsewhere), ovoid to narrowly ellipsoid, with circumscissile dehiscence. Seeds 1 to several per locule, often strongly mucilaginous when moistened. About 270 species, nearly worldwide.

A recent molecular study (Ishikawa et al., 2009) provided data that indicate that some of the polyploid taxa in the genus originated from hybridization events long ago, in some cases involving relatively distantly related species groups. The Missouri species of Plantago are wind-pollinated (except in cleistogamous flowers) and some of the more abundant, weedy species produce sufficient pollen to contribute to hayfever allergies. Steyermark (1963) noted that the young foliage of the broader-leaved species can be cooked as a vegetable.