A review of the genus Macromitrium Brid. (Orthotrichaceae, Bryophyta) in New Caledonia Author Thouvenot, Louis Saint Léon, 66000 Perpignan (France) thouvenot. louis @ orange. fr louis@orange.fr text Cryptogamie, Bryologie 2019 2019-10-16 20 16 167 217 http://dx.doi.org/10.5252/cryptogamie-bryologie2019v40a16 journal article 10.5252/cryptogamie-bryologie2019v40a16 1776-0992 12215595 Macromitrium humboldtense Thouvenot et Frank Müll. ( Figs 2B , 9 ) Cryptogamie, Bryologie 37: 296-299, figs. 1-6, 8-16 (2016). TYPE . — New Caledonia . South Province , Mt Humboldt, c. 1600 m , 31.VIII.2003 , F .Müller NC763 ( holo- , DR !; iso- , PC [ PC 0723602]!). ILLUSTRATIONS AND DESCRIPTION.— Thouvenot & Müller (2016) . DISTRIBUTION IN NEW CALEDONIA . — This species was found on ultramafic rocks in montane scrubland of Mt Humboldt, at 1600 m a.s.l. one of the highest altitudes in New Caledonia. It is candidate to micro-endemic status since it is only known from a single collection on the summit of Mt Humboldt which is an isolated high mountain in the large southern ultramafic massif of Grande Terre, the main island of the archipelago. TOTAL RANGE. — Endemic to New Caledonia , South Province . DESCRIPTION Macromitrium humboldtense is a very distinctive species characterised by: 1) a soft habit, when dry, leaves irregularly twisted, loosely spirally arranged, the apical parts of the leaves often wavy, with the unevenly oriented tips producing a shaggy effect; 2) short branches 3-7 mm long; 3) large branch leaves 3.6-4.6 mm long, narrowly lanceolate to narrowly triangular, regularly decreasing in width from the basal 1/8, long acuminate, ending in a piliform apex, hyaline or red-brown at the tip, up to 250 µm long; 4) laminal cells papillose, the upper cells mainly rounded quadrate, pluripapillose, occupying more than ¾ the leaf length, the transitional cells few, unipapillose, the lower cells long rectangular to linear, with straight lumina, extending only a short distance from the base, smooth or cells in the higher basal part with a single papilla; 5) setae 15-20 mm long, flexuous and smooth; and 6) calyptrae naked. Among these characters, the shape of the piliform apices is noteworthy since they have the appearance of long aristae, but the laminae really extend in wings along both sides of the costae, so that the costae are mainly percurrent or excurrent in a short point.