Bazzania exempta J.J.Engel
Bazzania exempta J.J.Engel, J. Hattori Bot. Lab. 99: 197. f. 1, 2. 2006.
Holotype: New Zealand, North Is., Wellington Prov., Tongariro Natl. Park, Mangawhero River near juncture of Rimu Track and Forest Walk, just NE of Ohakune, 625 m, Engel 22709 (F); isotype: (AK).
Plants strongly anisophyllous, delicate and fragile, soft and flexuous, prostrate and growing very loosely on substrate, pale olive-green, the older shoots becoming more deeply so; shoots medium, to 3 mm wide. Branching common, monopodial and not pseudo-dichotomous, the branches nearly exclusively ventral-intercalary, either leafy and then often becoming leading shoots or stoloniform and geotropic, with very reduced scale-like leaves and underleaves; Frullania -type branches very rare (one branch seen). Stems ± slender. Rhizoids from stem at immediate bases of both underleaves and leaves of stoloniform branches or from basal cells of the underleaves and leaves; rhizoids sporadically developed on leading leafy shoots, from stem at immediate base of underleaves. Leaves caducous, subopposite, horizontal, spreading at ca. 90° from stem, approximate to barely and loosely imbricate, with much of stem exposed in dorsal aspect; leaves not vittate, 400–550 µm wide × 1200–1500 µm long, distinctly incubous, plane or the distal sector of the leaf weakly deflexed, the leaves symmetrically to asymmetrically sublinear-ligulate, straight or weakly falcate; apex straight or, often, moderately oblique, asymmetrically (2)3-dentate, the median tooth the largest or the 2 dorsal teeth subequal in size but larger than the ventral tooth, which is often basal in juxtaposition to the median tooth, the ventral tooth at times comprised of only a few cells, the teeth acute to subacuminate, terminating in a single cell or a uniseriate row of 2(3) cells, the terminal cell tapering to a rounded, thick-walled summit, the leaf apex otherwise entire; dorsal margin variable, not ampliate (the leaves then ± symmetric) to moderately ampliate and broadly and gently arched (the leaves then ± asymmetric), usually not extending to middle of stem, subcordate at base, the margin somewhat irregularly repand, otherwise entire; ventral margin straight, often irregularly weakly repand, entire. Cells of leaf differentiated into a broad band of enlarged, subisodiametric to at most slightly elongated cells in the median longitudinal portion of the leaf (a subvitta), the subvitta occupying most of leaf width; cells smaller and subquadrate near the margins; median cells slightly longer than wide, 23–29 µm wide × 24–34 µm long, thin-walled, with trigones lacking or at most straight-sided and inconspicuous, the cells surrounded mostly by the thin cell walls, the trigones somewhat more strongly developed near the margins and at the leaf apex (where they may be medium and straight-sided); surface smooth. Underleaves weakly to moderately spreading, free on both sides, the shape somewhat variable: quadrate to sporadically subcuneate, to suboblate and then broader than long, or subrectangular and then slightly longer than broad; apex ± regularly to somewhat irregularly 4–5-lobulate to ca. 0.1–0.2 and with sinuses often of unequal depth, the lobules rounded at the summit and terminating in a slime papilla, variable in size and at times reduced to a low bulge consisting of several laterally juxtaposed cells with a median-placed slime papilla, the lobe margins entire; apex hyaline (decolorate) distally, the hyaline sector variable in size, often restricted to a zone that includes only the lobes, at times occupying as much as the distal 0.35 of underleaf; margins of disc entire, often repand, occasionally with a tooth or lobule in median sector, often subcordate at the base; cells with walls thin, trigones and surface as in leaves. Asexual reproduction by caducous leaves, the complete leaf falling away, or, often, the leaf base remaining.
Androecia and gynoecia not seen.
Comments : This species differs from all other representatives of the genus by the near absence of terminal branching (only one seen). Branching is monopodial and nearly strictly ventral-intercalary, with both stoloniform and leafy branches present (Fig. 105: 1). The leafy branches are common and become leading shoots that, in turn, produce a ventral-intercalary leafy branch (Fig. 105: 1). Shoots may produce several leafy branches in rather close proximity, but no branching pattern of any sort ensues. Since the plants virtually entirely lack Frullania -type branching, the freely and repeatedly pseudo-dichotomous branching pattern that is so typical of the genus is absent.
The species is also unusual in having intramarginal cell walls uniformly thin and with trigones lacking or at most minute (Fig. 106: 1, 2). Trigones are developed only near the margins and at the leaf apex and in both loci they may be medium and straight-sided (Fig. 106: 2, 3). In both cases, however, the cells are surrounded mostly by the thin walls (Fig. 106: 1 right, 2, 3). The genus Bazzania typically has cell walls slightly to distinctly thickened, particularly in the subapical sector of the leaf, and trigones that are small to bulging and nodulose.
The leaves are caducous, but somewhat irregularly so—the complete leaf may fall away (Fig. 105: 1), or, frequently, the majority of the leaf may fall away and only the base remains. The arrangement and form of the leaf are distinctive. The leaves are horizontal, spread at about 90° from the stem and are essentially plane, although the distal sector at times is feebly deflexed (Fig. 105: 2). Leaf shape is somewhat variable and grades from symmetrically to asymmetrically sublinear-ligulate, even on the same axis (Fig. 105: 4–9). This variation is largely due to differences in the curvature of the dorsal margin: when the margin is not or only feebly ampliate, the leaves are then ± symmetric and oriented straight (Fig. 105: 7), but when the margin is moderately ampliate and broadly and gently arched, the leaves are then ± asymmetric and weakly falcate (Fig. 105: 4, 5).
