Despite its small size, Tetraphis pellucida is a distinctive moss. Unlike most mosses which have 8, 16, 32 or even 64 peristome teeth, Tetraphis has only four teeth. When not fruiting, it frequently reproduces asexually by means of few-celled gemmae produced in tiny bowl-like whorls of leaves --gemae cups --at the tip of its erect stems.


Tetraphis has two distinct personalities habitat-wise. It occurs either on well-decayed wood (and very organic soil that is actually mostly well-decayed wood) or (totally inorganic) moist shaded sandstone ledges!


Note: many mosses reproduce asexually by simple fragmentation. A few produce specialized asexual reproductive structures. When present, they are useful in identification.

• Gemmae are small and simple, consisting of clusters of a few cells each.
• Propagula (also called brood branchlets) are miniature shoots with leaves. 

Mosses are often described according to their overall growth form, as belonging to one of two broad categories: acrocarps ("cushion mosses"), which are erect with sporophytes at the tips (tops) of the stems, and pleurocarps ("carpet mosses"), which generally lay flat and are much-branched, with sporophytes produced at intervals in the axils of the branches. This distinction is a major division of the moss key, roughly analagous to the way leaf arrangement (alternate and opposite) figues so prominently in tree keys.

The Crum key is actually divided into 2 separate keys: acrocarps and pleurocarps.


After growth form (acrocarp vs. pleurocarp), the Crum key uses cell surface, i.e, smooth vs. papillose (or some other type of projection such as mamillosity) as the next major step. After that, there's a wide array of leaf, cell, and sporophyte features, including those described in earlier pages here.