Schistochila gradsteinii Thouvenot, 2021

Thouvenot, Louis, 2021, Schistochila gradsteinii sp. nov., a new species from New Caledonia related to S. vitreocincta (Schistochilaceae, Marchantiophyta), with a key to the local species and a description of the gynoecium of S. integerrima, Cryptogamie, Bryologie 20 (2), pp. 11-18 : 13-15

Schistochila gradsteinii Thouvenot sp. nov.

( Figs 2; 3A, B )

DIAGNOSIS. — Stems with a one-layered cortex of thin-walled cells and unevenly thickened medullar cells; leaves conduplicate, the ventral lobes larger, oblong-lanceolate, acuminate, tapering to acute or apiculate apices, margins entire, the dorsal lobes inserted on the dorsal surface of the ventral lobes in a slightly curved line, the free margins not reaching the ventral lobe margins; leaf cells uniform with large three-layered trigones as in Schistochila vitreocincta ; underleaves lacking.

TYPE. –— New Caledonia. North Province, Hienghène, Ouaïème rocks, coordinates UTM 58 K: 0485 E, 7717 N, 22 Sept. 2019, Thouvenot NC2807 (holotype PC [ PC 0712100]; isotype in author’s private herbarium).

ETYMOLOGY. — This species is dedicated to Professor Stephani Robbert Gradstein, eminent specialist of the tropical liverwort flora, especially of the Lejeuneaceae . The author would like to express his gratitude for the invaluable support and friendly encouragement that Professor Gradstein provided him thorough his researches.

DISTRIBUTION. — Endemic to New Caledonia.

HABITAT. — Known only from the type, in North Province of New Caledonia, growing on the trunk of small trees in cloud forest, at 950 m elevation.

DESCRIPTION

Dioicous (?).

Plants

Light yellow green to light brownish; shoots simple, creeping and attached by dense rhizoids along almost the whole length of the plant, canaliculate with the leaves curved upward.

Stems

0.55 mm wide, 18 cells across, with an obvious epidermis made of 1-layered thin-walled cells 25-37 µm in diameter, hyaline, surrounding medullar cells (28) 40 (50) µm in diameter, unevenly thickened, walls variously multi-stratified, whitish, the corners thicker but without well-defined trigones.

Leaves

Distichous, spreading at angles 90-120°, entire, without a border of hyaline cells, ventral lobes usually 5.50 mm long, 2.25 mm wide, oblong-lanceolate to oblong-ovate, apices from acuminate-acute to obtuse-apiculate, ending in a file of up to six uniseriate quadrate cells, dorsal lobes distinctly smaller and narrower, 3.75 mm long, 1.75 mm wide, inserted on the dorsal surfaces of the ventral lobes in a slightly curved line, the free margins not reaching the ventral lobe margins, oblong-ovate, apices truncate to rounded, not or hardly exceeding the insertion line; leaves fragile, apices often broken and margins eroded so that broken cells in the border release cell contents enclosed in thin membrane in the form of ephemeral stellate chips.

Underleaves

Lacking.

Leaf cells

Similar in both lobes, without a border of differentiated hyaline cells, cells more or less uniform, rounded, 30-35 µm in diameter, walls thin, at angles with seemingly 3-layered thickenings ( Fig. 2J, M) as in Schistochila vitreocincta , the internal layers consisting of small, rounded trigones, surrounded by large circular areolae, eventually confluent, colourless, the external layers made of a thin membrane and agglutinated cell contents.

Gynoecia

Terminal, 7.5 mm long, bracts laciniate, bracteoles bifid, at most up to the base, lobes sublinear canaliculate to tubular, perianth narrowly tubular, 4-plicate, plicae widely rounded, split at least half of the total length, four lobes secondarily divided and laciniate; androecia not seen.

COMMENTS

Schistochila gradsteinii sp. nov. is easily distinguished from the other Schistochila species lacking underleaves by the combination of the following characters:1) ventral leaf lobes acuminate to obtuse-apiculate, the apices usually piliferous; 2) dorsal lobe insertion curved, apices rounded, free margins not reaching the ventral lobe margins; 3) both lobes with margins entire; 4) ventral side of stems matted with rhizoids along almost their whole length; 5) leaf cells with large three-layered trigones; and 6) stem structure with an epidermis of thin walled cells and medullary cells unevenly thick walled.

The new species resembles S. vitreocincta in distichous leaves with entire margins, the huge 3-layered trigones, the thin-walled epidermis cells and the absence of underleaves, but differs from that species in the dorsal leaf lobes being distinctly smaller than the ventral lobes (slightly larger than ventral lobes in S. vitreocincta ) and the leaves without a hyaline border (with a broad hyaline border in S. vitreocincta ). In its characters the new species seems morphologically intermediate between S. vitreocincta and other members of the genus Schistochila , especially those of the genus Gottschea which is phylogenetically close to S. vitreocincta ( He & Glenny 2010; Sun et al. 2014). It resembles also the entire margined S. integerrima , but in this species the ventral lobes have rounded apices and the dorsal lobe free margins exceed the ventral ones. Furthermore, the leaf cell trigones are of simple structure and the stem cellular pattern is very different, with the outer cells thick walled, smaller but little different from the underlying cells.

The transverse section of the stems in all other Schistochila species observed ( S. aligera , S. caledonica , S. integerrima and S. sciurea ) is consistent with the description of this structure in the publications on Schistochila , with relatively homogenous cells, of subequal sizes, and wall thickness gradually decreasing from the moderately thick cortical to the thin innermost cells. In contrast, S. vitreocincta has an epidermis of thin-walled cells (a hyaloderm) and significantly thicker medullar cells, with multi-layered walls. The new species has the same pattern, but the pattern is less conspicuous since the medullary cell walls are unevenly thick-walled and irregularly multi-layered. Interestingly, S. integerrima shows a tendency to have a differentiated epidermis made of a layer of cells smaller than the innermost cells, that is thick walled, and the medullar cells are unevenly thickened, but the differentiation is subtle ( Fig. 3 ).

A C B D E I F G H J K L M

The unusual structure of the leaf cells of Schistochila gradsteinii sp. nov., also observed in Bazzania kokawana N.Kitagawa & T.Kodama and S. vitreocincta might provide endogenous gemmae which are realeased in the environment when the fragile leaves broke, as stressed by Kitagawa (1983), taken up by Schuster & Engel (1985). In S. vitreocincta , according to Kitagawa (1983), the innermost layer is the true trigone, the median layer is an empty space and the outermost layer is the wall of a “daughter cell”. When cell walls break out, the cell contents enclosed by the membrane bordering the giant trigones are released into the surrounding area like stellate chips with truncate arms. In Schistochila gradsteinii sp. nov., each cell in the young leaves has the same pattern which gradually deteriorates in the oldest cells. The cell contents are enclosed in a membrane that looks like the endogenous gemma of S. vitreocincta . But, unlike in S. vitreocincta and Bazzania kokawana , whose cells contain numerous dark oilbodies and whose membrane of the released daughter cell is thick, making it able “to endure unfavorable environmental conditions” ( Kitagawa 1983), in S. gradsteinii sp. nov., the oil bodies are not persistent and the “daughter cells” are thin-walled, so that they are fragile and we could not find any evidence of the ability of the cells produced by S. gradsteinii sp. nov. to persist and propagate in the environment. Therefore, experimentation with more available material is required in order to test the ability of such cells to act as propagules.

Figures

FIG. 3. – Transverse sections of stems of: A, B, Schistochila gradsteinii Thouvenot sp. nov.; C, S. vitreocincta (Herzog) X.L.He et Glenny; D, S. aligera (Nees et Blume) J.B.Jack et Steph. E, S. integerrima Steph. A, B from the holotype, C from Thouvenot NC1732, D from Thouvenot NC671, E from Thouvenot NC2825. Scale bars. A, C-E: 20 µm, B, 100 µm.