Herbs, annual or biennial. Stems heteromorphic, sterile prostrate or decumbent to ascending, glabrous, fertile erect, glabrous or glandular-pubescent distally. Leaves cauline, whorled on sterile stems, alternate, sometimes whorled proximally, on fertile stems; petiole absent or essentially so; blade not fleshy, not leathery, margins entire. Inflorescences terminal, spikelike racemes; bracts present. Pedicels present; bracteoles absent. Flowers bisexual; sepals 5, proximally connate, calyx ± symmetric, short-cupulate, lobes linear-lanceolate or lanceolate to narrowly ovate or oblong; corolla white to blue or pale violet, bilaterally symmetric, bilabiate and personate, tubular, tube base not gibbous, spurred abaxially, lobes 5, abaxial 3, adaxial 2, abaxial lip much longer than adaxial and strongly arched at palate; stamens 4, proximally adnate to corolla, didynamous, filaments glabrous; staminode 0 or 1, minute; ovary 2-locular, placentation axile; stigma capitate. Fruits capsules, 2–4.8 mm, dehiscence poricidal by 4 or 5 irregular valves in each locule. Seeds 100–200, black or gray, angled, wings absent. x = 6.
North America, Mexico, South America, introduced in West Indies, e Europe, Pacific Islands.
Species 4 (3 in the flora).
Species of Nuttallanthus native to the New World have been included historically in Linaria; F. W. Pennell (1919, 1935) included them in the invalidly published sect. Lectoplectron Pennell. Sutton erected Nuttallanthus to accommodate these species based on their corollas with larger abaxial lips relative to adaxial lips, weakly developed palates, and less well-developed spurs, and their angled, four- to seven-ridged seeds. M. Fernández-Mazeucos et al. (2013) presented molecular evidence for the monophyly of Nuttallanthus as a member of one of three basal clades within Linaria. Support for two of the three basal clades, including one containing Nuttallanthus, was sufficiently low that the authors concluded that further studies were needed to determine whether Nuttallanthus should be included in Linaria as a section. Consequently, Nuttallanthus is maintained here as a distinct genus. Nuttallanthus subandinus D. A. Sutton occurs in South America.
Nuttallanthus species usually grow in well-drained, sandy soil in native plant communities that experience disturbances and also in disturbed habitats, including former cropland. The species sometimes grow in mixed populations; the North American species are cross incompatible (P. T. Crawford and W. J. Elisens 2006).
In the descriptions, corolla length is the distance from the distal point of the medial lobe of the abaxial lip to the distal point of the spur. In addition to chasmogamous flowers, cleistogamous flowers are produced early and late in the reproductive cycle. Fruits produced by cleistogamous flowers are smaller and contain fewer seeds than do fruits produced by chasmogamous flowers (P. T. Crawford and W. J. Elisens 2006).
|1||Corolla spurs 0.1–0.5 mm; pedicels 6–14 mm in fruit, ascending, sometimes erect, hairs to 0.3 mm.||Nuttallanthus floridanus|
|1||Corolla spurs 2–11 mm; pedicels 1.8–8(–9) mm in fruit, erect, hairs to 0.1 mm.||> 2|
|2||Edges of seeds sharp, faces obscurely tuberculate; corollas 8–14 mm, spurs 2–7 mm.||Nuttallanthus canadensis|
|2||Edges of seeds rounded, rarely angled or irregularly dentate, faces prominently pointed-tuberculate, rarely with rounded ridges and scattered, rounded tubercles; corollas (11–)14–22 mm, spurs 4.5–11 mm.||Nuttallanthus texanus|