Phytoneuron 2012-39: 44. 2012.
Annuals, shallowly fibrous-rooted or slender-taprooted, sometimes rooting at proximal nodes. Stems erect or basally ascending-erect, simple or few-branched, becoming fistulose in larger plants, (2–) 10–30 (–100) cm, delicately short glandular-villous to stipitate-glandular, often glabrous below inflorescence. Leaves usually cauline, basal sometimes persistent, distal connate-perfoliate, often bractlike; petiole: proximals 4–10 (–15) mm, distals 0 mm; blade: proximals sometimes subpinnately veined, usually with (1 or) 2 pairs arising from midvein above base, becoming palmately veined distally, ovatelanceolate to ovate or broadly ovate-elliptic, mid cauline 12–40 (–50) × 10–25 (–45) mm, base rounded to truncate or cuneate, margins shallowly dentate-serrate to serrate, teeth 7–12 per side, apex rounded to obtuse, surfaces glabrous, sometimes with sharp-pointed hirtellous, vitreous-flattened, or gland-tipped hairs. Flowers herkogamous, (1–) 3–14, usually from mid-stem and distally, chasmogamous. Fruiting pedicels 10–40 mm, delicately short glandular-villous to stipitate-glandular, often glabrous below inflorescence. Fruiting calyces nodding 30–90º, broadly campanulate, inflated, sagittally compressed, 9–13 (–15) mm, sparsely glandular-villous to stipitate-glandular, throat closing, adaxial lobe distinctly longer. Corollas pale-yellow, palate and abaxial throat dark yellow, drying blue-green, red-spotted, bilaterally symmetric, bilabiate; tube-throat funnelform to subfunnelform, (7–) 9–14 mm, exserted 3–4 mm beyond calyx margin; limb broadly expanded (8–17 mm pressed), palate densely bearded. Styles hirtellous. Anthers included, glabrous. Capsules included, 5–8 mm. 2n = 28.
Phenology: Flowering Jan–Jun.
Habitat: Stream and canal sides, pool edges, canyon bottoms, sand, gravel, and mud, riparian habitats, pine-oak forests.
Elevation: 200–2000 m.
Ariz., N.Mex., Mexico (Chihuahua), Mexico (Sonora)
Erythranthe unimaculata is recognized by its annual duration (fibrous-rooted, without stolons or rhizomes), delicate-glandular vestiture, mostly sessile to subsessile, often widely spaced leaves, closed fruiting calyces, and relatively large, pale yellow to nearly white corollas with a dark yellow palate that commonly dries blue-green. The breeding system is allogamous. Plants commonly are single-stemmed and usually erect but sometimes produce decumbent-ascending stems branching from the base, these sometimes rooting at proximal nodes.
Erythranthe unimaculata is known from Cochise, Gila, Pima, and Santa Cruz counties, Arizona, and from Doña Ana County, New Mexico.