Plants in thin to dense mats, light- to yellowish-green, glossy. Stems to 20 ´ 1--2 mm, simple or irregularly branched; epidermal layer of stem cells somewhat large with thinner exterior walls than interior, 1-several layers of smaller inner thick-walled cortical cells. Leaves flaccid, close or sometimes distant, erect-spreading, occasionally secund, often appearing distichous, subconcave, smooth, 0.5 --1.5 ´ 0.2--0.4 mm, lanceolate to slenderly ovate-lanceolate, symmetric, gradually long-acuminate, margins plane to erect throughout, entire or sometimes minutely serrulate at apex, often with 1--2 cells distinctly serrulate in alar region; median cells 96--156 ´ 5--7 µm; alar cells differentiated only on margins, 1--3 quadrate to short-rectangular cells, 16--31 ´ 7--9 µm, sometimes lacking. Specialized asexual reproduction rarely present, propagules, 33--61 ´ 9--14 µm, composed of 2--5 cells, green to yellowish green. Sexual condition autoicous. Seta red to reddish brown, 1--2 cm. Capsule yellow to orange-brown, subcernuous to cernuous, rarely erect, straight to subarcuate, 0.5--2.5 mm, oblong to ovoid, contracted below mouth when dry; operculum conic to conic-apiculate, 0.2--0.3 mm. Spores 9–14 µm.

Capsules mature spring to late summer. Acidic cliff crevices, rocky banks, sometimes calcareous soil and soil on overturned tree roots, bases of trees, decaying wood; 15--2270 m; Greenland; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Nun., Ont., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Maine, Mich., Minn., Mont., N.H., N.J., N. Mex., N.Y., Oreg., Pa., S.Dak., Utah, Vt., Wash., Wyo.; Mexico (Veracruz); South America (Argentina, Chile); Europe; Asia; Africa; Pacific Islands (New Zealand).

Isopterygiopsis pulchella is autoicous, and often produces sporophytes, while the other two species of Isopterygiopsis are dioicous and usually sterile. This species is further distinguished by the erect-spreading, sometimes secund, lanceolate to slenderly ovate-lanceolate, gradually acuminate, nondecurrent leaves with entire or minutely serrulate margins at the apex and base.

The epidermal stem cells of I. pulchella and I. alpicola are scarcely enlarged, only somewhat thin-walled and not as distinctly differentiated from the interior cortical cells as those of the type species of Isopterygiopsis, I. muelleriana. All three species, however, have papillose rhizoids in the leaf axils, as well as clusters of 2–6 celled cylindrical or fusiform gemmae in the leaf axils, and both characters readily place them in Isopterygiopsis. Orthothecium intricatum (C. J. Hartman) Schimper and O. strictum Lorentz may be confused with I. pulchellum in the Arctic but both species are dioicous and rarely produce sporophytes. Also, plants of Orthothecium have mostly straight, erect-spreading leaves rather than secund leaves like I. pulchellum. The Utah record is that of S. Flowers (1973). William Weber (personal communication) noted that Orthothecium diminutivum (Grout) H. Crum, Steere &L. E. Anderson (Holmgrenia diminutiva Grout) described from Colorado is synonymous with I. pulchella because of its papillose rhizoids and its multicellular, cylindrical brood bodies.