Monographs Details: Isotachis
Authority: Fulford, Margaret H. 1963. Manual of the leafy Hepaticae of Latin America--Part I. Mem. New York Bot. Gard. 11: 1-172.
Description:Genus Description - Leafy stems small to robust, pale green or pale rose to dark red, magenta, or brown, prostrate, ascending or becoming erect, in tufts, mats, cushions, or scattered among other bryophytes, simple to irregularly branched below, the branches leafy, of unlimited growth, ventral-intercalary, in the axils of underleaves or as subfloral innovations from the female bracteoles; stem in transverse section with a medulla of thin-walled cells surrounded by one to three layers of smaller, usually thick-walled cortical cells. Rhizoids when present colorless, in fascicles from the basal part of the underleaves. Line of leaf insertion oblique, the leaves incubous. Leaves ovate, ovate-truncate, oval, or orbicular in outline, symmetric or asymmetric, bifid to one-half of their length into two equal or subequal triangular, entire to coarsely dentate or ciliate segments; cells of the lamina irregularly rectangular in outline, or quadrate near the margins and in the segments, the walls thin to more or less thickened, with or without trigones and intermediate thickening, the cuticle smooth to striolate-papillose. Underleaves nearly equal to the leaves or smaller, approximate or imbricate, occasionally reflexed, symmetric, bifid, the margins as in the leaves. Plants dioicous. Male inflorescence terminal becoming intercalary on the stem or branch, the bracts similar to the leaves, the lamina concave, the bracteoles similar to the underleaves; antheridia large, globose, mostly in pairs in the axils of the bracts, the stalk six to eight cells long. Female inflorescence terminal on the stem or branch, the bracts and bracteoles in three series, symmetric or nearly so, similar to the leaves, larger, often more deeply divided and more strongly toothed, the inner series sometimes smaller, often adnate and carried up on the perigynium; archegonia 8-10; sporophyte enclosed in a slender, hollow, cylindric, thick-walled perigynium with a very short, reduced perianth at the top. Shoot/sporophyte relationship a free, fleshy shoot-calyptra with old archegonia over its surface. Sporophyte capsule ovoid-cylindric, the four valves spirally twisted, the wall of three layers, the outermost layer of large cells with radially thickened walls, the two inner layers of smaller cells with both radial and tangential thickenings; seta long, thick; elaters long, tapering at the ends, bispiral, brown; spores small, brown, smooth.
Discussion:Type species: Isotachis lyallii Mitten in J. D. Hooker, Bot. Antarct. Voy. 2(2): 149. 1855.
A high degree of variability in size and color of the plants and in the size and configuration of the leaves and underleaves and the teeth of their margins is present in plants of many of the species. The latter was well illustrated by Hatcher (1960), who made a comparative study of large numbers of the leaves and underleaves of certain of the species.
Some of the species formerly included in the genus have the general appearance and stem structure of an Isotachis but they produce perianths. The genus Triandrophyllum was one of these groups of species. A few others have not yet been transferred since the problem of relationships has not satisfactorily been solved because the material is sterile. These latter, together with those species for which no type has been available, are listed after the descriptions of the species.