Plants large. Stems pinnate or irregularly 2-pinnate. Stem and branch leaves similar, ovate; margins serrulate in distal 1/5; costa single; medial laminal cells less than 4:1. Seta stramineous, rarely reddish tinged, to 1.5 cm. Capsule erect, symmetric; operculum inclined-rostrate; peristome somewhat reduced.
Bestia has a confusing taxonomic history, which causes difficulty in determining its family placement depending on which species of Bestia was examined and what combination of morphological characters was considered most important for inferring relationships (J. R. Shevock et al. 2008). H. A. Crum (1987) placed Bestia in close relationship to Isothecium, in Brachytheciaceae. Bestia vancouveriensis was transferred to Thamnobryaceae as Porotrichum vancouveriense and subsequently elevated to generic rank as Bryolawtonia vancouveriensis.
Although Bestia has been attributed to several families, recent DNA studies suggest that Bestia and Isothecium are closely related and belong to Lembophyllaceae. Bestia is morphologically similar to some species of Isothecium (especially I. myosuroides), but it has several distinguishing gametophytic features, primarily medial laminal cells uniformly short (less than 4:1) whereas the juxtacostal cells in Isothecium are elongate to 8:1. The long, straight, cylindric capsules with smaller peristome teeth differ markedly from the rather hypnaceous curved capsules in Isothecium.