Macromitrium pulchrum var. neocaledonicum (Besch.) Thouvenot, 2019

Thouvenot, Louis, 2019, A review of the genus Macromitrium Brid. (Orthotrichaceae, Bryophyta) in New Caledonia, Cryptogamie, Bryologie 20 (16), pp. 167-217 : 203-204

Macromitrium pulchrum var. neocaledonicum (Besch.) Thouvenot , comb. nov.

( Fig. 18)

BASIONYM. — Macromitrium neocaledonicum Besch., Annales des Sciences naturelles, Botanique, sér. 5, 18: 211 (1873).

TYPE. — New Caledonia, “in monte Mou, 1200 m, Balansa 2980 cum M. pulchro socium” (lecto-, fide Vitt in Sched. [1983] BM [ BM 000982735]; isolecto-, PC [ PC 0137835, 0137836, 0096506]!).

DISTRIBUTION IN NEW CALEDONIA. — Rarely found in South Province.

TOTAL RANGE. — Endemic to New Caledonia.

SELECTED SPECIMENS. — New Caledonia. Province Sud, Païta, Dzumac massif, in mountain forest with understorey dominated by Cyperaceae , in ultramafic massif, 915 m, 18.IX.2008, Thouvenot NC230.

REMARKS

Macromitrium neocaledonicum is very similar to M. puchrum whose it shares most traits except: 1) in dry condition, leaf apices less tightly enrolled; 2) in wet condition, leaves spreading recurved instead of erect-spreading; 3) branches usually longer with fastigiated branchlets, up to 20 mm

long, the perichaetia developing at apices of branchlets or single main branches; 4) upper leaf shape narrowly ligulate, rounded to obtuse and mucronate at apices instead of lanceolate acute; and 5) upper cells more evenly isodiametric, less thick-walled.

These typical features were used by Bescherelle to define M. neocaledonicum as a species since they are well expressed in the type specimen. However, we could observe among type specimens in PC or more recent collections some samples lacking one or more of these characters, e.g.: 1) samples with simple and shorter branches can be considered as included in intra-specific variability. Fastigiated branches are quite rare in New Caledonian Macromitrium and we are not aware of their value as a specific discriminating character; 2) samples may possess lanceolate leaves with narrowly obtuse to acute apices. In these cases, the plants are intermediate between M. neocaledonicum by their dry/wet habit and M. pulchrum by their size and leaf shapes; and 3) the type of M. pulchrum var. densirete has branches with fastigiate branchlets, smaller cells and narrowly rounded leaf apices, like M. neocaledonicum , but with the shape of M. pulchrum branches when moist. Due to these various patterns in the features used to discriminate these two taxa, we do not retain the specific status for M. neocaledonicum . However, it seems necessary to keep in mind this well characterized “form”, especially because the type specimen of M. neocaledonicum was found mixed in a sample of M. pulchrum . It could hide different evolutionary processes that cannot be understood at this stage of knowledge and needs further studies involving more material and molecular studies. Besides, the difference in the wet habit of the leaves could be interesting regarding adaptation to ecological constraints (see above in the Francii group paragraph). Therefore, we provisionally propose a varietal status.