Monographs Details: Hookeria
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants medium-sized to robust, in lustrous, light-green or rarely yellow-green, flat, often thin mats. Stems creeping, simple or irregularly and little-branched, the branches not differentiated, complanate-foliate; in cross-section all cells thin-walled, outermost cells not differentiated, central strand present, of somewhat smaller cells; rhizoids tufted at base of stems, from stems and leaf bases, bright brick-red, roughened; pseudoparaphyllia none; axillary hairs 2-3-celled, hyaline, with a short basal cell and 1-2 elongate apical ones. Leaves slightly or not contorted when dry, crowded, the lateral and dorsal leaves slightly differentiated, the lateral ones ± spreading, ± asymmetric, the dorsal ones ± erect, ± symmetric, all ovate to broadly ovate, obtuse to acute; margins obscurely bordered by a single row of longer, narrower cells, subentire or distantly crenulate, plane; costa none or obscurely short and double; cells lax, hexagonal, smooth, thin-walled, ± porose, becoming somewhat shorter in the extreme apex, not or only scarcely differentiated toward insertion; alar cells not differentiated. Asexual propagula rhizoid-like, produced on leaf apices and marginal and submarginal laminal cells, similar diameter, color, and ornamentation to rhizoids but with straight rather than diagonal crosswalls, perhaps acting as propagula. Autoicous. Perichaetia relatively small, inconspicuous; leaves few, lanceolate, with areolation similar to vegetative leaves. Setae elongate, smooth, dark-yellow to orange, ± straight but often geniculate at base and curved at apex; capsules ± erect to inclined or horizontal to ± pendent, ovoid to short-cylindric, symmetric; exothecial cells subquadrate to short-rectangular, strongly collenchymatous sometimes with additional median thickenings; annulus of large, very thick-walled cells, usually falling with the operculum; operculum conic-rostrate; columella broadly cylindric, ca. ½ the length of the urn; peristome double, attached at the mouth, exostome teeth bordered not shouldered, on front surface with a zig-zag median line, not furrowed, cross-striolate below, papillose above, trabeculate at back; endostome with a medium to high basal membrane, segments keeled, perforate, with baffle-like crosswalls, ca. as long as the teeth, cilia none. Spores spherical, finely papillose. Calyptrae mitrate, of large, short-rectangular cells, not lobed or with a few short lobes at base, naked, smooth.
Discussion:Discussion. Hookeria is characterized by relatively robust, complanate-foliate plants. The hexagonal leaf cells are very large and can even be seen with a hand lens The leaves are mostly ecostate and obscurely bordered. The setae are smooth and the capsules symmetric. The exostome teeth have a zig-zag median line and are cross-striolate below. The calyptra is remarkable in the distinct, short cells, rather than the typically obscure elongate ones. Like all other genera in the family, the calyptra is several cells thick at its base, as illustrated by Janzen (1917: 214).
The plants appear to lack pseudoparaphyllia. However, this is probably more closely related to the branching pattern of the plants than to any phylogenetic consideration. Frequently when pleurocarps grow in heavily shaded habitats they are little branched and rather put most of their growth into the primary stem. This occurs in species of Plagiothecium and Taxiphyllum as well as in Hookeria. It seems to be primarily an adaptation to habitat.
Hookeria has weakly differentiated cells in the center of the stem that, because of their position, are best interpreted as a central strand. However, they seem to differ from other stem cells only in size, although they occasionally have thinner walls than adjacent stem cells. There is no evidence they are functional. Even if they are not, there is some morphological evidence that most stem cells can potentially transport water, at least by capillary action. In cross-sections, end walls are sometimes chanced upon, and in every case the walls are perforate with (2-)5-10 holes; they are never solid. One can only assume that these aid in water conduction.