Plants green above, deep purple below and along margins, which are undulate and slightly ascending; branching by numerous short intercalary lateral branches that arise beneath main thallus; dichotomous branches few. Thalli 10 30 ´ 2 4 mm; epidermis smooth, cells 30 40 ´ 20 30 µm, the walls slightly thickened, trigones small or lacking, oil cells few, scattered; air pores scarcely elevated, with 2 3 tiers of 7 8 cells around the opening; ventral scales deep purplish red with scattered oil cells; appendages 1 2 purplish or hyaline, lanceolate to acuminate. Sexual condition autoecious, sex organs on short latero ventral intercalary branches; androecia on very short clavate branches, the androecia ovate, without surrounding scales; gynoecia on short, obcordate branches, stalks reddish, 1 3 cm with sparse hair like scales at apices, few or none at bases; carpocephala high domed and bell shaped, 2.4 4 mm across, usually 4 lobed, the lobes directed obliquely downward; pseudoperianths white or reddish tinged, 10 12 cleft, the segments connate at apices. Sporophyte capsules yellowish brown; spores yellow to pale brown, 65 100 µm; elaters yellow to pale brownish, 2( 3) spiral, 150 220 µm.

Capsules mature Mar.--May. Soil of shaded banks; Calif., sw Oreg.

The presence of frequent, short, intercalary branches and paucity of dichotomous branching distinguishes this species from others of the genus in the flora. The principal thalli often curl when dry, exposing the dark purple underside. Asterella bolanderi subsp. acrogyna R. M. Schuster named from a single Texas collection (R. M. Schuster 1985), was a specimen of Reboulia, later treated (R. M. Schuster 1992) as Reboulia hemisphaerica subsp. acrogyna (R. M. Schuster) R. M. Schuster.