Phytoneuron 2012-39: 38. 2012.
Annuals, filiform-taprooted. Stems prostrate to ascending-erect, sharply bent at basal nodes, simple or few-branched, 5–25 cm, glandular-puberulent to glandular-villous, hairs 0.1–0.8 mm, vitreous, flattened, multicellular, gland-tipped. Leaves basal and cauline, largest at mid-stem; petiole 6–30 mm; blade pinnately veined, broadly lanceolate to ovate, 10–35 × 10–30 mm, distinctly membranous, base cuneate to shallowly cordate, margins coarsely dentate to shallowly denticulate or entire, apex acute to obtuse, surfaces glandular-puberulent to glandular-villous, hairs 0.1–0.8 mm, vitreous, flattened, multicellular, gland-tipped, glandular. Flowers herkogamous, 1–6, from proximal to distal nodes. Fruiting pedicels divergent at right angles from stem, usually closely paired, 10–45 mm, negatively phototropic, causing capsules to pressed against a cliff face or crevice at time of dehiscence, glandular-puberulent to glandular-villous, hairs 0.1–0.8 mm, vitreous, flattened, multicellular, gland-tipped. Fruiting calyces angled, tubular-campanulate, slightly inflated, 5–7 mm, margins distinctly toothed or lobed, sparsely stipitate-glandular, lobes pronounced, erect. Corollas light yellow, throat and abaxial lobes red or purple-spotted, sometimes with small white patches, bilaterally symmetric, weakly bilabiate; tube-throat funnelform, 10–14 mm, exserted beyond calyx margin; lobes obovate-oblong, apex rounded to truncate or notched. Styles glabrous. Anthers included, glabrous. Capsules included, 3–6 mm. 2n = 32.
Phenology: Flowering Apr–Aug(–Sep).
Habitat: Steep, seasonally moist, basalt cliffs with west or southwest exposure, mesic coniferous forests.
Elevation: 800–1300 m.
Idaho, Mont., Oreg.
In the protologue, R. J. Meinke observed that plants of Erythranthe hymenophylla have reflexed fruiting pedicels that increase seed dispersal back onto the vertical cliff wall, the characteristic habitat of the species. The hanging habit of E. hymenophylla is reflected in a sharp (90º to 180º) bend in the basal nodes and the long pedicels that are closely paired and divergent in parallel at about right angles from the stem. The species also is characterized by it very short calyx to corolla length, relatively short capsules, and large seeds.