Large for a moss, with large leaves. Plants are of two kinds,usually occurring togehter. Fertile plants are upright, with leaves forming a tuft, from which arises the capsule containing the spores. In upright plants, largest leaves are at the top. Vegetative (sterile) plants are flattened, with leaves spreading to either side. Largest leaves are generally near the bottom.

The picture at right show, left to right, a fertile plant, a sterile plant, and a fallen spore capsule with its stalk. At left you can see fertile plants (above) and vegetative plants photographed in the field. The fertile plants had produced capsules earlier, some of which were fallen between the plants. Below left shows a fertile plant photographed in the studio, while the middle photo is a similar picture of a vegetative plant

Leaves are identical in both kinds of plants. They are about 1 mm long, oval, with a pointed tip. Each leaf has a prominent midvein (called a costa in mosses) that extends all the way to the tip and beyond as a little hair. Each leaf has several tiny teeth above the middle, although these are very difficult to see without a microscope. Tiny teeth and and the little hair at the tip are visible in the picture below right, which was taken under a microsocpe at 100x magnification.

Grows on rocks, logs, tree bases and the ground in wet to moist woods. Found pretty much all over North America and also in Europe and Asia. In Wildwood, common on rocks in the floodplain of Connelly's Run, especially near the South Bridge.

The common name thyme moss comes from its mimicking a sprig of an herb. The common name baby tooth moss presumably refers to its tiny teeth.

Saber tooth moss (P. ciliare) is a close relative that looks very similar. It has long teeth along the entire edge of the leaf from base to tip. That species is also very common and could occur in Wildwood. Another similar relative is P. drummondi, but in Virginia that species is found only in Fairfax and Chesapeake counties on the coast.