Chiastocaulon raetzelii Frank Müll., 2021

Müller, Frank & Thouvenot, Louis, 2021, Chiastocaulon raetzelii (Marchantiophyta, Plagiochilaceae), a new species from New Caledonia, Phytotaxa 521 (4), pp. 237-243 : 238-241

Chiastocaulon raetzelii Frank Müll. , sp. nov. Figs. 1–2

Diagnosis: The species is characterized by very fragile, caducous leaves; on most parts of stem, leaves have fallen off; persisting only on basal parts of stem; bract leaves of androecia are permanent and often the only ones remaining on the stem. Plants minute, leafy shoots to 1 mm wide, stem diameter 85–170 µm, leaves 0.5–0.9 mm long, 0.3–0.8 mm wide. Leaves on leafy shoots in opposing pairs, obovate-truncate to spathulate, teeth 3–7 per leaf, filiform, with long rectangular cells, teeth occupying about 1/3 to 1/4 the entire leaf length. Both antical (dorsal) and postical (ventral) margin of leaves are straight to shallowly arched towards base, the postical margin reaching ventral stem midline. Cortical stem cells light brown. Antheridial bracts in 6–10 pairs.

Holotype: — NEW CALEDONIA. South Province, Nouméa 45 km N, Mont Humboldt , ascend from the south to the mountain hut below the summit, epiphytic in mossy forest, ca. 1200 m, 21°54’S, 166°24’E, 30 August 2003, F. Müller NC 811 ( DR).

Description: Plants with shoots weakly differentiated into a creeping or erect leafy sector and a creeping stolon, both sections irregularly and frequently branched, stolons bearing reduced leaves; plants forming loose, diffuse turfs, yellowish brown; leafy shoots erect-ascending, up to 25 mm long and 1 mm wide, monomorphic, flagellae absent. Branching exclusively ventral-intercalary, with or without a subsidiary ventral-intercalary branch producing a positively geotropic stolon at the base of the primary. Stems reddish-brown to brown, 85–170 µm diameter, surface smooth, in cross section transversely elliptic, cortical layer 1 or 2 cell tiers deep, cortical cells slightly smaller than the medullar, with heavily thickened and light brown walls that constrict the cell lumen, walls evenly thickened, medulla 3–4 cells high, number of medullar cells 9–15, lumen clearly wider than in cortical cells, the cell walls less thickened, only cell corners more thickened. Rhizoids mainly on the stolons, arising in loose fascicles from the base of the leaves, also scattered on ventral and lateral stem surfaces. Leaves extremely caducous; on most parts of the stems, usually remaining only on basal part of stems, otherwise male bracts more persistent, all surrounding vegetative leaves absent. Leaves on leafy shoots in opposing pairs, remote to contiguous, transversely orientated and widely spreading; leaves obovate-truncate to spathulate, 0.5–0.9 mm long, 0.3–0.8 mm wide, usually as wide as long or indistinctly longer than wide; on dorsal side leaves standing close together or more often dorsal leaf bases connate dorsally, antical (dorsal) margin straight to shallowly arched, very slightly decurrent, postical (ventral) margin straight to gently arched towards base, oriented parallel to the stem, attaining the dorsal stem midline; apex truncate to spathulate, not lobed, apical margins and partly ventral margins with 3–7 very prominent filiform teeth, dorsal margins in general entire, seldom with one tooth, teeth to 320 µm long, at base 2–6 cells wide, the longer teeth with uniseriate tip of 3–6 cells, these cells long rectangular, 24–56 µm long, 10–21 µm wide, filiform teeth occupying 1/3 to 1/4 the leaf length; cells of leaf margin quadrate to rectangular, mostly wider than long, 13–23 µm long, 18–30 µm wide, walls evenly thickened; cells in mid-leaf variably sized and shaped, subquadrate to elliptic, 25–38 µm long, 19–28 µm wide, cell walls evenly thickened with indistinct to distinct bulging trigones; cells in leaf base longer, quadrate to rectangular, unequally sized, 32–50 µm long, 15–32 µm wide, arranged in loose tiers, with coarse cordate to bulging trigones and less thickened intermediate walls, grading into surrounding mid-leaf cells; cell surfaces smooth and unornamented. Oil-bodies unknown. Underleaves lacking. Dioicous.Androecia spike-like, solitary, intercalary on shoots that continue vegetative growth, male bracts closely imbricate, toothed like vegetative leaves, saccate, in 6–10 pairs. Gynoecia not seen. Sporophytes not seen.

Additional material seen (paratypes): NEW CALEDONIA. South Province, Dumbéa, along the hiking trail from Auberge du Mont Koghi to Mont Bouo , epiphytic in montane rainforest, ca. 800 m, 22°10’S, 166°31’E, 09 September 2001, F. Müller NC 97 ( DR); Païta, summit of Mt Mou , 1219 m, amongst bryophytes on twig in dwarf cloud forest, 17 September 2016, Thouvenot NC 1975 (Thouvenot private herbarium) .

Etymology: The species is named in honour of Stefan Rätzel, an enthusiastic German botanist, specialist of a wide range of plant groups. He accompanied the senior author on his second visit to New Caledonia and pointed out in the field some easily overlooked bryophytes.

Distribution and ecology: Known only from New Caledonia, reportedly limited to the South Province, where it was found in montane rainforests on ultrabasic substrates at elevations from 800 to 1200 m. On Mont Humboldt it was found growing together with Dicnemon cuspidatum Bescherelle (1873: 191) , Drepanolejeunea sp. , Heteroscyphus sp. , Bazzania francana ( Stephani 1924: 463) Kitagawa (1972: 446) , and Radula amentulosa Mitten (1861: 367) , on Mont Bouo with Pleurozia articulata ( Lindberg 1869: 78) Lindberg & Lackström (1874: 5) and Heteroscyphus aselliformis ( Reinwardt et al. 1824: 412) Schiffner (1910: 172) , and on Mont Mou it was growing mixed with Solenostoma hirticalyx ( Stephani 1924: 87) Schuster ex Váňa et al. (2010: 137) , Metalejeunea cucullata ( Reinwardt et al. 1824: 227) Grolle (1995: 100) , Frullania chevalieri ( Schuster 1970: 289) Schuster (1992: 34) and others.

Figures

FIGURE 1. Chiastocaulon raetzelii. A–B. Habit of male plants. C. Habit of male plants with defoliated vegetative parts. D. Plants with persistant vegetative leaves only on basal parts. E–F, I. Shoots in dorsal view. G–H. Shoots in ventral view. A–C, E–H from the holotype, D, I from Müller NC97.

FIGURE 2. Chiastocaulon raetzelii. A. Shoot portion, dorsal view. B–C. Shoot portion, ventral view. D–L. Leaves. M. Androecium. N. Marginal cells of leaf. O. Cells in upper part of leaf. P. Median cells of leaf. Q. Basal cells of leaf. R. Ventral intercalary branching. S–T. Upper part of male shoots lacking caducous vegetative leaves below androecia. U. Transverse section of stem. V. Marginal teeth of leaf. A–E, H–N, P, R–V from the holotype. F–G, O, Q from Müller NC97.