Trichostomum tonghoueensis Thouvenot, 2021

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 : 192-193

Trichostomum tonghoueensis Thouvenot , nom. nov.

Hymenostomum aristatulum Broth. & Paris Öfversigt af Finska

Vetenskaps-Societetens Förhandlingar 51A (17): 11 (1909).

TYPE. — New Caledonia. Tonghoué, ad viam inter Nouméa et Païta, VII.1905, Le Rat s.n.; (iso-, PC [ PC 0697667!]).

OTHER SPECIMENS EXAMINED. — New Caledonia. South Province, Yahoué, alt. 150 m, VII.1910, Franc s.n. ( PC [ PC 0735859]); Dogny plateau, alt. 900 m, I.1911, Franc s.n. PC [( PC 0735862]).

DESCRIPTION FROM THE ISOTYPE IN PC

Habit

Plant small, gametophyte 2-3 mm high in dry condition, 4 mm high when wet, with sporophyte 8-10 mm high. When dry, leaves erect incurved to circinate, concave to canaliculate, costae conspicuous on the back; when wet, patent, straight above the recurved sheathing base.

Stem

Simple, shorter, 0.15 mm wide, cortical cells well defined, 1-2 layers of cells, smaller and thicker walled and orange-brown tinged, central strand present.

Leaves

Somewhat different in size and shape, the lower smaller 1.4- 1.5 mm long, 0.4-0.45 mm wide, ligulate obtuse, mucronate, wider above middle, the upper 1.8-2.4 mm long, 0.45-0.6 mm

wide, ligulate to lanceolate, acute, aristate, aristae up to 150 µm long, basal part relatively short, oblong-rectangular, hyaline, upper part slightly concave, opaque, margins plane, sub-entire; costae strong, excurrent, ventral cells like the laminal, costa section ovate-reniform, 58 µm wide, 32 µm high, ventral epidermis present, verrucose, dorsal epidermis null, four guide cells, dorsal stereid band larger than the ventral.

Cells

Upper cells opaque, 5-7 µm wide, quadrate-hexagonal, firm walled, slightly bulging on both sides, with many low papillae; basal cells smooth, translucent, wide rectangular-elongate, thin-walled, narrower and thicker-walled toward margins, transitional cells smooth, short rectangular, thick-walled, not ascending along the margins.

Perichaetial leaves

Like the upper vegetative.

Sporophyte

Setae 6-7 mm long, capsules elliptical, stegocarpous, opercula rostrate, rostra oblique 0.6 mm long, urns 1.5 µm long, peristome null; spores 18-22 µm, finely verrucose.

COMMENTS

As the genus Hymenostomum is now a synonym of Weissia (Chen, 1941 ex Zander, 1993) , we have checked the types of the New Caledonian species still linked to Hymenostomum , in order to evaluate their transfer towards Weissia versus other Trichostomoideae ( Trichostomum , Chionoloma , Hyophila ). But this species does not match with Weissia characters, lacking crispate leaves in dry condition and involute margins. We transfer it to the genus Trichostomum , on the basis of the following characters: dry leaves erect incurved, concave, margins plane, entire, transition of the basal parts gradual, not ascending along margins, costal section with dorsal stereid band larger than the ventral. It differs from other New Caledonian Trichostomum species by the absence of peristome and the aristate upper leaves. Trichostomum species have usually obtuse to sub-acute, mucronate leaf apices and peristome with 16 short narrow teeth. T. noumeanum (Thér.) Thouvenot is quite similar but is a smaller plant, with leaves up to 1.5 mm long and setae up to 1.7 mm long.

The name Trichostomum aristatulum Broth. being already published for an Australian species ( Brotherus 1916), we choose the name Trichostomum tonghoueensis for the New Caledonian plants, after the name of the type locality (article 6.11 of the International Code of Botanical Nomenclature of Shenzen, Turland et al. 2018).