Detailed description: Plants typically small, shoots to 750 µm wide, variously pigmented but often brown to red-brown or almost black; Frullania-type and Lejeunea-type branching; leaf-lobe with entire margins and acute or acuminate to apiculate apices; underleaves with entire lateral margins or at most with minor angulations or rarely with 1 pair of very small inconspicuous teeth; lobules ± remote from the stem (lobule attached to stem by 23 cells) and at angles of (25) 4575º with the stem so that lobules tilted outwards; lobules with a conspicuous projecting, angular cell, inserted directly above the lateral slit (mouth); styli conspicuous, triangular to rectangular, large, broad based; and leaf-lobes without a conspicuous group of basal ocelli; bracts and bracteole of 1-2 pairs, entire, marginal teeth absent; a single archegonium per gynoecium; perianth freely emergent at maturity, 3-keeled with the keel margin sharp to obtuse, and contracted toward the apex into a cylindrical beak; asexual reproduction; none known.
Affinities and notes: Frullania truncatistyla has very close morphological affinities with the two South American representatives of F. sect. Amphijubula, F. lobulata and F. microcaulis. Unlike these species, F. truncatistyla has a large, distinct, rectangular stylus with an almost truncate apex that immediately differentiates it from either of these species (Fig 3.4, 3.6). The dioicous state, the large size of the lobules in comparison to the lobe (Fig 3.3, 3.4) and the sparingly branched growth pattern, also distinguish F. truncatistyla from F. microcaulis. Frullania truncatistyla may easily be confused or overlooked as a small form of the Australasian F. rostrata, but the latter can always be separated from F. truncatistyla by the absence of the conspicuous projecting cell above the lobule mouth and the smaller triangular styli. Interestingly, this is one of a suite of taxa that appear to be very uniform and lack any notable variability. The distinctive Chevalieri-type initial branching appendages (vide von Konrat & Braggins 2001) may vary in terms of their frequency but the plants otherwise appear to be fairly uniform.
Useful references: von Konrat, M.,J. Hentschel, J. Heinrichs & J.E. Braggins. (2011). Deep Southern Hemisphere Connections: A Revision of Frullania sect. Amphijubula. The Bryologist. 114(1): 52-66.