Radula notabilis M. A. M. Renner

[From NSW909500, NSW909501 and BRI-AQ722865] Forming loosely interwoven mats on tree trunks, branches and twigs, either tightly adherent on or hanging from substrate. Live plants nitid brown-green, fading to brown in herbarium. Shoot systems irregularly and often infrequently branched, female plants predominantly pseudodichotomous due to production of pairs of subfloral innovations below gynoecia. Shoot systems monomorphic, 1.4–2.0 mm wide and up to 40 mm long, branches initially smaller in stature than parent shoot but attaining similar stature by fourth of fifth pair of leaves. Older shoot sectors retaining leaf-lobes, though older leaf lobes may partially fragment on some shoots. Stems 135–160 µm diameter, with cortical cells in a single tier of 14–26 rows; outer half brown-pigmented, inner half tan-pigmented; external free cortical cell wall heavily and continuously thickened, radial longitudinal cortical walls thin or slightly thickened, inner tangential walls heavily and more or less continuously thickened by fusion coarse nodular trigones; medullar cells in 15–32 rows, with coarse nodular trigones, lacking thickenings between trigones, occasionally with heavily and continuous thickenings, all unpigmented or faintly yellow pigmented. Cortical cells on dorsal stem surface arranged in straight longitudinal rows on young and mature shoot sectors. Leaf insertion not reaching dorsal stem mid-line, leaving one or two dorsal cortical cell rows leaf-free; leaf insertion not attaining the ventral stem mid-line, leaving two ventral cortical cell rows leaf-free. Leaf lobes rotund-elliptic to elliptic-oblong, 950–1145 µm long by 610–820 μm wide, contiguous to imbricate, not falcate, acroscopic base not sharply deflexed away from stem, plane, not interlocking over the dorsal stem surface, stem visible between leaf lobes in dorsal view; lobe margins irregular and crenulate, the interior lobe margin sometimes minutely auriculate, not or only just reaching the opposite stem margin, antical margin shallowly curved, becoming substraight in larger leaf lobes, sharply curved through nearly 90° in exterior quarter, exterior margin shallowly curved or straight, sharply curved through nearly 90° in postical quarter, postical margin straight; angle between postical lobe margin and keel c. 135°. Lobules rhombiform when small, transitional as stature increases to trapeziform with exterior and interior margins nearly parallel, one sixth to one fifth the lobe area, 370–735 µm long by 260–480 μm wide, keel straight in rhombiform lobules, arched in trapeziform lobules, angle between keel and stem 135°, keel gradually turning through 90°, keel apex and postical lobe margin flush, interior lobule margin free for one quarter to one third its length, free portion weakly ampliate on rhomboid lobules to moderately ampliate on trapeziform lobules, extending at most half way across the ventral stem surface, acroscopic margin S-shaped to curved, apical portion inclined toward stem in smaller lobules, transitional to perpendicular to stem axis in larger lobules, apex acute in rhomboid lobules transitional to obtuse in trapeziform lobules, free exterior margin straight to shallowly curved, occasionally with a small knee above the lobe-lobule junction, margins plane, crenulate; lobe-lobule junction antical to the acroscopic end of stem insertion, lobule attached to stem along 0.66–0.75 of the interior margin, stem insertion more or less linear, gently curved at acroscopic and basiscopic ends, not revolute; a single papilla present at the lobule apex and another two papilla situated on the interior lobule margin above the stem insertion. Leaf lobe cells rounded-oblong, not arranged in rows, unequally sized, 16–26 µm long by 11–19 μm wide, thin walled with triangular trigones, medial wall thickenings absent; cells of lobe margin smaller than those of leaf middle, quadrate to rectangular, 9–15 µm long and wide, interior cell walls evenly and continuously thickened, exterior cell wall thickened differentially at midwall, causing exterior margin to be crenulated, cell lumen not bulging medially; leaf lobe cell surface unornamented, smooth. Oil-bodies not known. Asexual reproduction possibly by caducous leaf lobes but sporadic, older shoot sectors usually retaining most or all of their leaf-lobes, with fragmenting leaf-lobes tearing into several pieces, fragmentation scars jagged, irregular, typically leaving part of basiscopic leaf margin attached beyond keel, shoot primordia forming as irregular buds on leaf lobe after leaf fragmentation. Dioicous. Androecia on indeterminate branches that continue vegetative, androecial bracts in 4–8 pairs, lobules epistatic, keel deeply curved, bucket-like, free apical portion triangular, apex obtuse, moderately deflexed, lobes rounded, not caducous, antheridia not seen. Gynoecia terminal on leading shoots and branches, subtended by one or two full sized subfloral innovations that are again fertile, where a single subfloral innovation is present, a ‘resting’ shoot primordium occurs in place of the second subfloral innovation; archegonia 140–170 µm tall, up to 16–18 per gynoecium on a small raised disc of tissue, encompassed by the protoperianth, archegonia neck eight cell columns; female bracts in one pair, asymmetrical, tightly imbricate, oblong-obovate, larger lobe 665–720 μm long by 440–475 μm wide, smaller lobe 620–650 μm long by 350–370 μm wide, lobules rectangular, one half the lobe area, apex obtuse to broadly acute, keel arched, margins crenulate, insertion interlocking dorsally but not ventrally, insertion equitant. Perianths 2800–3800 µm long, conical and flared at mouth, mouth irregularly repand 880–950 µm wide. Perianth walls unistratose above, with bistratose bands extending up to half way up perianth, increasing in width toward base, becoming confluent, basal perianth walls progressively increasing in thickness, 2–3 stratose. Long stem perigynium present, 5-6 stratose, external cell wall thickened and brown-pigmented, internal walls unthickened and unpigmented. Calyptral perigynium present, base of calyptra bistratose at base, unistratose above, unfertilised archegonia elevated on surface of calyptra.

Radula notabilis is endemic to the Wet Tropics of north-eastern Queensland, where it is a common epiphyte in riparian rainforest in the tropical lowlands, from the edge of the coastal plain to approximately 300 m asl. Radula notabilis is rarely found far from running freshwater, and is usually encountered on tree trunks and branches over or adjacent to watercourses where itoften forms closely adherent mats or pendant-procumbent wefts on bark, and does not often inhabit dense multi-species epiphytic turfs.