Radula imposita M. A. M. Renner

[From NSW896812] Forming tufts of overlapping and interlocking shoots on leaves and twigs, bright- to mid-green when fresh, fading to a glossy tan or brown in herbarium; shoot systems densely irregularly pinnately branched in female plants, with additional pseudodichotomous branching in fertile female plants due to production of pairs of subfloral innovations below gynoecia; monomorphic, 0.8–1.2 mm wide and up to 30 mm long, branches smaller in stature than parent shoot; older shoot sectors retaining leaf-lobes. Stems 80–130 µm diameter, with cortical cells in a single tier of 15–30 rows; cortical cell walls yellow-brown to brown pigmented; external free cortical cell wall heavily and continuously thickened, radial longitudinal cortical walls thickened or not, inner tangential wall more or less continuously thickened; medulla cells in 10–25 rows; cell walls yellow-brown pigmented, with medium-sized triangular to weakly bulging trigones, walls between trigones lacking thickenings or continuously thickened; cortical cells on dorsal stem surface arranged in straight longitudinal rows on young and mature shoot sectors. Leaf insertion reaching dorsal stem mid-line or not, leaving zero or one dorsal cortical cell rows leaf-free, in some shoots stem growth appears to have introduced an additional cortical cell row to the dorsal stem surface, in which case a single row of dorsal cortical cells is leaf-free, but this row is discontinuous between adjacent leaf pairs; leaf insertion not attaining the ventral stem mid-line, leaving two to four ventral cortical cell rows leaf-free. Leaf lobes elliptic-ovate, 430–700 µm long by 320–450 μm wide, larger on primary shoots, contiguous to imbricate, not to weakly falcate, acroscopic base not sharply deflexed away from stem, flat, patent, not interlocking over the dorsal stem surface, stem visible between leaf lobes in dorsal view; margins irregularly but minutely repand, crenulated due to medial wall thickenings on marginal cell walls, the interior lobe margin weakly ampliate, covering part of the dorsal stem surface but not often reaching the stem midline, and never exceeding the opposite stem margin, antical margin curved, exterior margin curved, postical margin curved to straight; angle between postical lobe margin and keel 45-60°. Lobules rhombic when small to almost quadrate, one sixth the lobe area, 175–345 µm long by 150–265 μm wide, larger on leading shoots; keel straight to curved, angle between keel and stem 135°, keel apex and postical lobe margin running into lobe margin smoothly or shallowly notched; interior lobule margin free for one eighth to one sixth its length, free portion not or weakly ampliate, not or hardly extending onto the ventral stem surface; acroscopic margin shallowly S-shaped, apical portion inclined towards stem; apex apiculate-rounded; free exterior margin straight to curved, margins plane, entire; lobe-lobule junction level with the acroscopic end of stem insertion in small and large lobules; attached to stem along 0.83 to 0.88 of the interior margin, stem insertion straight to curved, not revolute at acroscopic end; lobule apex bearing a single papilla, with another two papilla situated on the interior lobule margin above the stem insertion. Leaf lobe cells rounded-oblong, not arranged in rows, unequally sized, 11–22 µm long by 8–16 μm wide, walls slightly thickened their entire length, sometimes with small triangular trigones, medial wall thickenings absent; cells of lobe margin smaller than those of leaf middle, quadrate to rectangular, 9–14 µm long and wide, interior walls not differentially thickened, exterior walls with pronounced medial thickening, and medially bulging cell lumen; leaf lobe cell surface papillose, upper lobe wall differentially thickened over cell lumen forming a single low dome-shaped papilla over each cell. Oil-bodies not known. Asexual reproduction not known. Dioicous. Androecia not known. Gynoecia terminal on leading shoots, subtended by two subfloral innovations that are full-sized and again fertile; archegonia 145–160 µm tall, archegonia neck five or six cell columns, 6–8 per gynoecium on a small disc of tissue, encompassed by the protoperianth; female bracts in one pair, slightly asymmetrical with lobule on one larger than the other, imbricate, elliptic-ovate, lobe 520–570 μm long by 240–320 μm wide, margins irregular and crenulate; lobules rectangular-ovate, one half to two thirds the lobe area, apex rounded to obtuse, keel arched, irregular.

Known to date from four specimens, all growing over running streams on either leaves or bark including tree-trunks and branches. The specimens were collected in the North Coast of New South Wales, and in the Wet Tropics Bioregion of north-east Queensland.