2. Aureolaria Raf. (false foxglove)

Plants annual or perennial herbs, hemiparasitic, green or dark green, sometimes purplish-tinged, sometimes blackening upon drying. Stems erect or ascending, usually with several to many branches, rounded or bluntly 4-angled, glabrous (then often somewhat glaucous) or densely pubescent with glandular or nonglandular hairs, not roughened to the touch. Leaves opposite, sessile or short-petiolate, the petioles usually winged, sometimes nearly to the base. Leaf blades lanceolate to ovate in outline, more or less unlobed to deeply 1 or 2 times pinnately lobed or divided, the margins otherwise entire or toothed. Inflorescences open, terminal racemes with leafy bracts (these reduced progressively toward the axis tip), the flowers paired at the nodes, usually appearing as axillary flowers toward the stem tip, variously short-stalked to moderately long-stalked, the stalks somewhat thickened toward the tips, lacking bractlets. Cleistogamous flowers absent. Calyces 5-lobed, slightly to moderately zygomorphic, bell-shaped, the lobes slightly shorter than to longer than the tube, entire to toothed or lobed, persistent, becoming distended and slightly enlarged at fruiting. Corollas 30–60 mm long, 5-lobed, more or less bell-shaped, yellow, the tube somewhat curved or oblique, sparsely to densely short-hairy on the inner surface, the hairs not blocking the throat, the lobes shorter than the tube, spreading, their surfaces glabrous or glandular-hairy, hairy along the margins, the throat (also the outer surface of the tube) sometimes tinged with brownish markings. Stamens with the filaments of 2 lengths, hairy (at least toward the base), the anthers with 2 sacs, these more or less parallel, tapered to an awnlike base, light yellow to yellow, hairy. Style somewhat curved downward and often slightly exserted, the stigma club-shaped to more or less capitate, unlobed. Fruits 9–20 mm long, ovoid or ellipsoid, glabrous at maturity or glandular-hairy. Seeds 0.8–2.7 mm long, ellipsoid to oblong-ellipsoid or more or less trapezoid, usually slightly flattened, the surface with a fine to coarse network of ridges and pits, the ridges sometimes appearing winglike, brown to dark brown or black. Nine to 11 species, eastern U.S., Canada, Mexico.

The taxonomy of Aureolaria is in need of thorough revision. Pennell (1928) recognized eleven species, with most of the more widespread ones subdivided into a complex series of infraspecific taxa. Since then, there has been no comprehensive study of the systematics of the genus. However, some authors working on regional floras have eliminated some of the less widely distributed species or reduced these to infraspecific taxa under more widespread relatives. The treatment below is thus very preliminary, pending future studies.

Steyermark (1963) and many other authors also chose to treat this genus under the name Gerardia L. For further discussion, see the treatment of Agalinis above.

Species of Aureolaria have been documented to parasitize the roots of a number of woody species, including both pines and hardwoods, but have been documented most commonly on the roots of oaks (Quercus, Fagaceae) (Musselman and Mann, 1978; Werth and Riopel, 1979). The large, relatively open-throated flowers of Aureolaria are pollinated mainly by bumblebees (C. R. Robertson, 1891; Pennell, 1935). Ballard and Pippen (1991) documented a sterile putative hybrid between A. pectinata (as A. pedicularia) and A. flava in southern Michigan. Previously, Bell and Musselman (1982) had studied the breeding system and potential for hybridization among four Aureolaria species in Virginia. They found that interspecific hybrids among the perennial, obligately outcrossing species were generally fairly fertile. However, when pollen from the self-compatible annual or biennial A. pectinata (as A. pedicularia) was placed on the stigmas of perennial species, the crosses failed and when pollen from the perennial species served as pollen parents in crosses with A. pectinata, the resultant hybrid offspring had relatively low fertility. Although natural hybrids involving A. pectinata should be searched for in Missouri, they are likely to be very uncommon. Conversely, the degree of interspecific hybridization between A. flava and A. grandiflora has not been studied and may be relatively frequent. It may account for some of the patterns of pubescence and variation in leaf morphology exhibited by these two species. Members of the genus are mostly pollinated by bumblebees.