Theca

The thickness of exothecial cell walls in the descriptions of the genera presented here refers to that of the anticlinal walls. The superficial walls may be, and usually are, much thicker than the anticlinal walls (Pl. 59, f. 11; 79, f. 10). The stomates (Pl. 93, f. 8) are usually rather transparent compared to the other exothecial cells, but this is obvious only in split-open capsules. Stomates in the Pottiaceae are confined to the base of the capsule above or on the short neck, and their numbers are generally correlated with capsule size. They are seldom entirely absent, and variation among the genera is discussed by Paton (1957). The exothecial walls of Byroceuthospora, Eucladium, Trachycarpidium (Pl. 80, f. 9), Uleobryum (Pl. 89, f. 9) and species of Weissia are bulging, to a greater or lesser degree, while capsules of Ganguleea (Pl. 65, f. 10–11) and species of Weisiopsis (Pl. 67, f. 20) are distinctly plicate, or, in the case of Tetrapterum (Pl. 79, f. 10), are weakly winged.

Peristome

The peristomes of most taxa are either straight or nearly so, or are twisted to various degrees counterclockwise (as viewed from above with direction of twist coming upward); peristomes are seldom twisted clockwise. The counterclockwise direction of torsion is known as sinistrorse, and may also be described as the appearance of the threads of a standard, right-handed screw (right-handed because it is screwed in with an over-the-top right twist, not because the threads twist to the right). Of all genera studied, only Timmiella has, in some species, a peristome distinctly twisted clockwise; the peristome of Leptodontiella is either straight or very weakly twisted clockwise. Most genera have spiculose peristome teeth, while a few (e.g. Leptodontium) are characterized by smooth or striate peristome teeth. A basal membrane (Pl. 84, f. 12–13; 97, f. 16; 106, f. 9), may be differentiated in various genera.

Operculum

The operculum is usually rostrate and straight or weakly curved or inclined. When immature, rostrate opercula are often merely long-conic, e.g. as in Trichostomum brachydontium.

Calyptra

The calyptrae of Pottiaceae species are usually cucullate (Pl. 51, f. 11), but are sometimes mitrate (Pl. 42, f. 8) or conic-mitrate (Pl. 17, f. 17; 41, f. 9). Species of Microbryum, Hypodontium and Streptopogon may have papillose calyptrae.

Spores

A list of published electron micrographs of spores of Pottiaceae was given by Ireland (1987). In the present treatment the main character used taxonomically is relative size of the spores. Anisospory in the Pottiaceae is discussed in the treatment of Leptodontium.