Macromitrium macrosporum Broth.

Thouvenot, Louis & Müller, Frank, 2021, Contribution to the bryophyte flora of New Caledonia IV. Species new to the country, new localities together with taxonomic notes, Cryptogamie, Bryologie 20 (13), pp. 181-196 : 190-192

* Macromitrium macrosporum Broth.

SPECIMEN EXAMINED. — New Caledonia. North Province, Poindimié, Tango Plateau, alt. 300 m, on a fallen branch in a quarry, 11.X.2019, Thouvenot NC2920 (PC[PC0712108]).

DESCRIPTION

Habit

Plant growing in dense mats, stems long creeping, densely branched; branches short, erect, 10 mm long, 2 mm wide, rusty brown, the youngest part light green, when dry curly, with leaves individually twisted, the apices incurved to coiled, when wet with leaves erect-patent, the apices incurved, costa strongly prominent abaxially, making a groove adaxially in upper part.

Leaves

Narrowly lanceolate acuminate, 2.00- 2.75 mm long, 0.35- 0.45 mm wide near base, the bases slightly wider, evenly decreasing to the narrowly acuminate to shortly acute apices, at the end the lamina reduced to 1-2 ranks of cells along the costa, percurrent to very shortly excurrent, basal parts of leaf

differentiated by elongate cells very short, 1/₁₀ the whole leaf length, margins entire, recurved on one side in basal part.

Cells

Upper laminal cells 10-15 µm wide, lumina rounded, thick walled, bulging, mammillose, median and lower laminal

cells lined up, the median oblong, occupying a large part of the leaf length, with single rounded papillae, the lower ones elongate, 40-50 µm long, 10 µm wide, thick walled, porose, with narrow straight lumina and frequent single high papillae.

Perichaetial leaves

Erect, not sheathing, shorter than the normal leaves, up to 1.8 mm long, sub-triangulate, costae excurrent in short points, areolation like normal branch leaves.

Sporophytes

Seta to 10 mm long, smooth, straight, capsules small, ovoid, without neck, rim narrow, plicate, red-brown, peristome reduced to a whitish membrane, vaginula and calyptra naked.

COMMENTS

During a field trip in 2019, one of us (LT) collected a Macromitrium specimen that matched none of the species hitherto reported from New Caledonia ( Thouvenot 2019). The checked characters match the description of M. macrosporum ( Brotherus 1898, Vitt et al. 1995) from which it differs only by perichaetial leaves smaller than the vegetative ones. This only character is insufficient to define a different species since the other characters in a whole are similar. We were unable to observe male organs nor dwarf male plants on these fertile female plants which lack fresh sporophyte and the sexual status of this species remains unknown ( Vitt et al. 1995).

This plant occurs at high elevation in Papua-New Guinea ( Vitt et al. 1995) while it grows at lower elevation in New Caledonia. This ecological difference may be explained by the higher latitude and lower elevation of the highest ranges, capped at 1600 m asl in the latter country. The discovery of this species in New Caledonia increases the number of Macromitrium species in New Caledonia up to 25 and extends the range of M. macrosporum hitherto known from Papua-New Guinea, Indonesia and Philippines ( Vitt et al. 1995). It also confirms the affinity of the bryophyte flora in New Caledonia with Indo-Malaya.