Hygroamblystegium macroneuron Grout, Bryologist 36: 1, figs. 1-5. 1933; Eurhynchium macroneuron (Grout) H. A. Crum; Oxyrrhynchium macroneuron (Grout) Wynns

Stems 5-14 cm, branches to 10 mm. Stem leaves 0.9-1.5(-1.8) × 0.4-0.8 mm; costa excurrent, percurrent, or ending 3-6 cells before apex, 1/5-1/2 leaf sometimes laterally spurred; alar cells almost undifferentiated; laminal cells partly 2-4-stratose, 30-65 × 6-9 µm; basal cells 7-10 µm wide. Branch leaves 1-1.5 × 0.1-0.8 mm.

Rock, shallowly submerged in calcareous springs at base of limestone slopes in narrow canyons; moderate elevations (600 m); Tex.

The single known locality of Donrichardsia macroneuron is Seven Hundred Springs in Edwards County. This locality was described in detail by R. Wyatt and A. Stoneburner (1980), who also tried to find more localities in similar habitats nearby, but without success. Donrichardsia macroneuron has a very broad costa reminiscent of Hygroamblystegium noterophilum. The latter species has short, oblong-rhomboidal cells, never linear and flexuose.