Plants small, delicate, bright green, in dense to loose tufts. Stems 0.5--1 cm; erect, simple to sparingly branched. Leaves distant to laxly imbricate, erect to incurved when dry, erect-spreading to spreading when moist, 0.3--1 mm, ovate oblong to ligulate or ovate-lanceolate to ovate, apex broadly acute to rounded-obtuse; margins revolute throughout or plane distally and revolute proximally, bluntly serrulate by paired teeth; costa extending 7/8 of lamina or subpercurrent, rough abaxially distally; laminal cells lax, pellucid, thin walled, distal cells subquadrate to oblong rhomboidal, 20--30 × 10--12 µm, obscurely to clearly prorulose at distal ends, basal cells rectangular, 25--35 × 10--15 µm. Specialized asexual reproduction by occasional short brood branches in axils of distal leaves. Sexual condition dioicous. [Perigonia gemmiform, subtended by 1--5 branches, often appearing lateral. Seta ca. 20 mm. Capsule 1--1.5 mm, furrowed when dry; peristome as for genus. Spores reddish brown, 20--26 µm, papillose].

Moist, rocky, usually limey soil or in rock crevices; 0--1500 m; Ala., Fla., La., Miss., N.C., Kans., Okla., Tex; Mexico; Central America; West Indies; South America.

Sporophyte traits are as given by P.A. Florschütz (1964), who treated this species as a variety of Philonotis uncinata. Philonotis gracillima is distinguished in the floral range by the combination of a broad leaf apex (both broadly acute and rounded-obtuse apices may occur on the same plant), relatively short costa and the lax, pellucid leaf cells. Specimens of similar morphology have been collected from many parts of the Old World tropics under an older name, P. hastata (Duby) Wijk & Margadant. Further study is required to resolve this possible synonymy.