Brevianthus hypocanthidium M.A.M.Renner & J.J.Engel, 2015

Renner, Matt A. M., Engel, John J., Patzak, Simon D. F. & Heinrichs, Jochen, 2015, A new species of Brevianthus (Brevianthaceae, Marchantiophyta) from New Caledonia with unusual underleaf production, PhytoKeys 50, pp. 43-60 : 45-46

Brevianthus hypocanthidium M.A.M.Renner & J.J.Engel sp. nov. Figures 1 , 2

Diagnosis.

Distinguished from both subspecies of Brevianthus flavus by the triangular underleaves produced on small- to medium-sized shoot sectors, the consistently but shallowly bilobed leaves, the crenulate leaf margins formed by heavily thickened exterior cell walls, and the chlorophyllous marginal leaf cells similar in size to the medial cells.

Type.

New Caledonia, Province Sud, Mont Kouakoué, slightly west of base camp at helicopter landing site, without date, E.A. Brown 2006/17, holotype: NOU; isotypes: NSW, F.

Description.

Plants closely prostrate, creeping, shoots sinuous, dull whitish green, opaque, water repellent, axes cylindrical, vermiform, to 2 mm wide and 30 mm long, the axes slightly laterally flattened. Branches sporadic, lateral-intercalary. Stolons and flagellae absent. Stems wiry, narrow for plant size, densely papillose, cortical cells oblong, all walls heavily thickened, in cross section 7-8 cells high, cortex undifferentiated, cells same size as medulla, with massive, nodular thickenings either confluent or separated by short stretches of unthickened primary wall. Rhizoids scattered on ventral side of stem, colourless, non-septate, tips often branched. Leaf insertion strongly succubous, nearly horizontal at postical end, not recurved at antical end, extending to stem mid-line on ventral side of large, but not small shoots, not extending to dorsal stem midline, leaving 1-2 cell rows leaf-free. Leaves strongly dorsally assurgent, not connivent over the dorsal stem surface, the axis appearing channeled in dorsal view with the stem partly or completely visible, the leaves unistratose throughout, densely imbricate, concave, ovate-rotund, lacking a hyaline border; apex shallowly but distinctly bifid; margins crenulate by thickened cell walls; dorsal margin rounded, not or slightly decurrent, ventral margin rounded, the base weakly auriculate on small leaves and not auriculate on large leaves, not overlapping the ventral stem surface, not totally obscuring the stem in ventral view. Leaf cells not tiered, polygonal but typically hexagonal, isodiametric, with massive coarse, nodular trigones, confluent or separated by narrow stretches of unthickened primary wall, primary walls visible within trigones, 39-50 µm diameter; marginal cells thick walled, external wall heavily thickened, especially medially, trigones coarse, not confluent, consistently separated by unthickened primary wall, lumena not reduced, cells only slightly smaller than median cells, quadrate, 40-50 µm long and 27-36 µm wide, long axis parallel with margin. Intramarginal cells on abaxial surface covered with dense circular and confluent to bacilliform anastomosing ornamentation continuous over cell junctions; urceolate to clavate ‘papillae’ over cell junctions absent. Cells, both marginal and intramarginal, on adaxial surface with similar ornamentation, comprised circular and confluent to weakly anastomosing ornamentation. Underleaves present on small- to medium-sized shoot sectors, triangular, 4-6 cells wide at base and 8-9 cell tiers high, apex acute, formed by a single cell; 230-300 µm long by 9-140 µm wide at base, margins crenulate; ventral merophyte 0-2 cells wide. Asexual reproduction by leaf-borne regenerants arising from the adaxial leaf surface.

Sexual structures not seen.

Etymology.

hypocanthidium: υπο- hypo-, below; αχανθα- acantha (f.) spine, thorn, prickle; -ιδιον -idion, a diminutive suffix.

Distribution and ecology.

So far as known, endemic to New Caledonia. The type collection occurred on a ridge bearing forest 3 m tall with open canopy and high light at ground level, where it grew with Schistochila vitreocincta (Herzog) X.-L.He & Glenny at the base of the trunk on a 'mostly dead’ Leucopogon R.Br. The Schuster specimen occurred in an open, disturbed (old burn) Dacrydium araucarioides Brong. & Gris- Callitropsis Oerst. scrub.

Recognition.

The genus Brevianthus is highly distinctive among leafy-liverworts in the white or nearly white, water-repellent, cylindrical shoots with dorsally assurgent and succubously inserted leaves and no or inconspicuous underleaves, and scattered rhizoids. The shoots are typically sinuous in growth, either down or across the substrate, and lay closely appressed to it. They do not often overlap one another. This combination of macro-morphological characters facilitates field identification.

The three Brevianthus taxa recognized here all share these features, and are similar in their gross morphology. They differ primarily in micromorphological, microstructural, and anatomical details. However, characters vary in their manifestation with the stage of shoot stature and maturity, such that diagnostic differences must be sought within shoots of the appropriate age or size.

The triangular underleaves found only in Brevianthus hypocanthidium (Fig. 1L ) are a case in point. Not only are these partly obscured by adjacent leaves, they are produced only on small and medium sized shoot sectors. They are absent from the largest stature shoot sectors. As such, they are inconsistently present along a shoot, and may be entirely absent if the shoot examined is uniformly large. The other two Brevianthus taxa never produce underleaves, regardless of shoot stature.

Characters of the leaf apex and margins are useful in distinguishing the taxa of Brevianthus . The leaf apex of Brevianthus hypocanthidium (Fig. 1O ) is shallowly but distinctly bifid, and this is a consistent feature of leaves of all sizes, though on the smallest leaves of leaf-borne propagules this is obscure. In Brevianthus flavus subsp. crenulatus small leaves are bifid (Fig. 5O, P ), while medium and large leaves have an undivided apex (Fig. 5G-L ). In Brevianthus flavus subsp. flavus the leaf apex is always undivided and entire (Fig. 3E-J ).

The leaf margin provides several diagnostic differences between the three taxa that are of more consistent manifestation. In Brevianthus hypocanthidium the leaf margin (Fig. 1F ) is crenulate by virtue of its heavily thickened exterior cell wall, and the marginal leaf cells are chlorophyllous and similar in size to the medial cells. In Brevianthus flavus subsp. crenulatus the leaf margin (Fig. 5F ) is crenulate by virtue of bulging marginal cell lumena, and the marginal cells are colourless and smaller than medial cells. In Brevianthus flavus subsp. flavus the leaf margin (Fig. 3L ) is entire, the marginal cells are again colourless and smaller than medial cells.

Trigones in leaf-cells differ between species. In Brevianthus hypocanthidium (Fig. 1E ) they are block-like and angular with truncate ends and straight sides. In both subspecies of Brevianthus flavus (Figs 3L , 5F ) they are coarse to bulging but with curved sides, and never as large or angular as observed in Brevianthus hypocanthidium .

Leaf surface ornamentation may exhibit species-specific differences though there is intra-individual variation; our interpretation, however, may suffer from the relatively small number of observations we have made via SEM. Individuals of Brevianthus flavus subsp. flavus (Figs 3K ; 4C, D ) possess urceolate to clavate ‘papillae’ over the cell junctions on the abaxial leaf surface, at least between cells in the median-basal to basal portions of leaves, and at least sporadically on leaves along a single shoot. These ‘papillae’ have not been observed in individuals of Brevianthus flavus subsp. crenulatus (Figs 5E ; 6C, D ) or the type of Brevianthus hypocanthidium (Figs 1E ; 2C, D ). Parts of these structures are removable with chloroform, providing evidence that they partly consist of surface waxes ( Heinrichs and Reiner-Drehwald (2012)).

Other leaf characters differentiate the taxa. The interstices between cells also appears to exhibit species-specific differences. In Brevianthus flavus subsp. crenulatus (Fig. 6 ) leaf cell junctions appear recessed within the leaf such that the upper and lower parts of the cell appear surrounded by a narrow trench, which is less pronounced or absent in both Brevianthus hypocanthidium (Fig. 2 ) and Brevianthus flavus subsp. flavus (Fig. 4 ).

Leaf shape, orientation and imbrication also differ. In both Brevianthus flavus subsp. crenulatus (Fig. 5D, M ) and Brevianthus flavus subsp. flavus (Fig. 3D ) the leaves are imbricate over the ventral stem surface, obscuring stem tissue in ventral view, while in Brevianthus hypocanthidium (Fig. 1D, L, M ) the ventral stem surface is often partially visible between the leaves. The leaves of Brevianthus hypocanthidium (Fig. 1A, G-K ) are ovate-rotund, and when viewed in situ laterally, have their antical margin orientated more or less perpendicular to the stem. Brevianthus flavus subsp. flavus (Fig. 1A, E-I ) has ovate to oblate leaves whose antical margin is inclined in lateral view, with the lowest part of the margin closest to the shoot apex. The same is true of Brevianthus flavus subsp. crenulatus (Fig. 5A, H-L ) though the angle of inclination is not so steep.

Conservation status.

That Brevianthus hypocanthidium is known from two gatherings precludes inference of its likely distribution and abundance, we therefore recommend the species be considered Data Deficient.

Additional specimen examined.

New Caledonia, Montagne des Sources, above St. Louis: Pic Buse and vicinity, 650-750 m, R.M. Schuster 57820 (F).

Figures

Figure 1. Brevianthus hypocanthidium: A lateral view of shoot B dorsal view of shoot C habitus D ventral view of shoot E abaxial leaf cell surface F cell margin at leaf apex, one leaf-lobe featured G-K leaves dissected and flattened L underleaves M ventral view of shoot showing underleaf absence from largest shoot sector (middle of image) N regenerants on old shoot sector O leaf apex P stem transverse section Q ventral view of regenerant attached to adaxial side of single cell at shoot base, showing variable expression of triangular underleaves on distinct ventral merophyte R lateral view of stem, with apex to left, leaves removed showing linear succubous insertion, J-shaped at ventral end, note cells of stem insertion projecting ventrally S transverse section of stem showing dense ornamentation on dorsal stem surface. All from NSW 791547. Scale: 500 µm (A, B, D, G-K, M); 3000 µm (C); 50 µm (E, F, S); 200 µm (L, O, P, R); 1000 µm (N); 250 µm (Q).

Figure 2. Brevianthus hypocanthidium: A leaf apex B cells at base of sinus on abaxial leaf surface C abaxial leaf surface at mid-leaf D abaxial leaf surface scale E adaxial leaf surface scale F adaxial leaf surface detail scale. All from NSW 791547. Scale: 40 µm (A); 20 µm (B, E, F); 10 µm (C, D).

Figure 3. Brevianthus flavus subsp. flavus: A lateral view of shoot B dorsal view of shoot C habitus D ventral view of shoot E-I leaves dissected and flattened J leaf apex K abaxial leaf cell surface L leaf margin at apex. All from NSW 892112. Scale: 500 µm (A, B, E-I); 3000 µm (C); 1000 µm (D); 200 µm (J); 50 µm (K, L).

Figure 4. Brevianthus flavus subsp. flavus: A leaf apex scale B cells below apex on abaxial leaf surface scale C abaxial leaf surface at mid-leaf scale D abaxial leaf surface scale E adaxial leaf surface F adaxial leaf surface detail. All from NSW 89112. Scale: 60 µm (A); 40 µm (B); 20 µm (C, F); 10 µm (D).

Figure 5. Brevianthus flavus subsp. crenulatus: A lateral view of shoot B dorsal view of shoot C habitus D ventral view of shoot E abaxial leaf cell surface F cell margin at leaf apex, one leaf-lobe featured G leaf showing crenulate hyaline cells prominent on dorsal margin H-L leaves dissected and flattened M ventral view of shoot N leaf apex O dorsal view of regenerant showing bulging cells and bifid leaf apices P lateral view of regenerant attached to adaxial side of single cell near the leaf margin at shoot base Q lateral view of stem, apex to left. All from NSW 745726. Scale: 500 µm (A, B, D, H-M); 3000 µm (C); 50 µm (E, F); 250 µm (G, O, P, Q); 200 µm (N).

Figure 6. Brevianthus flavus subsp. crenulatus: A leaf apex B cells below apex on abaxial leaf surface C, D abaxial leaf surface at mid-leaf E, F adaxial leaf surface. All from NSW 745726. Scale: 20 µm (A, B, E, F); 10 µm (C, D).