Vittariaceae

Abstract

Epiphytic, less often epilithic, medium-sized to very small ferns; stem creeping or erect, protostelic (in the smallest forms) or solenostelic to dictyostelic, with transitional stages, dorsiventral if creeping, radial if erect, lacking sclerenchyma. Scales of stem clathrate, very often with metallic sheen, often seemingly toothed by marginally protruding radial cell walls; sometimes inconspicuous articulate hairs also present. Leaves simple, rarely forked or cleft, or pinnate, distichous or, on radial stems, polystichous, their bases non-articulate, with one or two vascular bundles, when mature without macroscopically evident epidermal appendages; petiole often short or virtually absent, otherwise mostly ill-defined, adaxially grooved like the costa but distinctly so only near the base. Costa present or not, percurrent or evanescent in the basal half of the lamina, rarely wanting; veins simple or forked and free, or pinnately branched and then joined by a submarginal commissure, or amply reticulate, the areoles open or closed at the margin; free included vein-lets never present. Stomata most often polocytic. Epidermis with characteristic mechanical cells containing silica spicules (“spicular cells”; Fig. 139F). Sporangia assembled in simple or branched soral lines, in one genus in roundish sori, in one other diffusely scattered over the surface; a true indusium always wanting but the soral lines often immersed in grooves of the leaf tissue, or protected by flanges of the lower leaf surface or by the revolute margin. Soral trichomes very often present, uniseriate, rarely branched, often with an enlarged and modified terminal cell. Sporangial stalk uni- or biseriate at the base, triseriate only at the extreme apex. Stomium four-celled, bow of annulus many-celled. Spores usually hyaline, smooth, without prominent perispore, trilete or monolete, sometimes both shapes present within a single genus.