Neckera praetermissa Enroth & Touw, 2015

Neckera praetermissa Enroth & Touw spec. nov. ( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Holotype: — VIETNAM. ”Vietnam borealis. Prov. Ninh-Binh. In reservato silv. Cuc-Phuong pr. pag. Bong. Ad corticem arborum cacuminis altissimis in alt. 600 m.s.m.”, 14. Dec. 1965, Pócs, Ninh & Bich s. n. (H, ex herb. EGR, “Expeditio tertia Hungaro-Vietnamica No. 3031/G”) .

Plants gregarious, somewhat glossy, old plants greyish-yellow. Stems to c. 3 cm long, short-stipitate, densely and sub(bi)pinnately to irregularly branched, frondose, fronds variable in outline. Most branches arising at c. 35–40 degrees angle relative to stem. Some branch tips naked due to caducous branch leaves. Stolons creeping, branching, stolon leaves to 0.8 mm long, sheathing, ecostate, from an ovate base at c. 4/5 leaf length narrowed to a lanceolate acumen, apex acute and often bearing few small teeth; laminal cells smooth, elongate, cell walls incrassate-porose, one row of marginal cells towards leaf base progressively shorter, more or less rectangular; rhizoids smooth, brownish-orange, unbranched or scarcely branched, in tufts situated just below leaf insertions. Stipe leaves 1.5–1.8 mm long, 0.6–0.8 mm wide, appressed and sheathing, shortly decurrent, ovate-lanceolate to ovate-lingulate, with a short, indistinct costa often bifurcate at base; laminal cells smooth, elongate, cell walls strongly incrassate-porose, leaf cells towards margins progressively shorter, one or two marginal row(s) consisting of more or less rectangular cells; alar cells distinct, oblong and rectangular to quadrate, with nearly solid walls. Stem leaves to c. 2.2 mm long and 0.5 mm wide at base, symmetric or nearly so, ligulate from an ovate base, decurrent, weakly plicate and erect-patent when dry, not much altered upon wetting, leaf apex acute. Branch leaves similar in shape as stem leaves, to 1.5 mm long and 0.4 mm wide; distal branch leaves often somewhat homomallous and appearing fasciculate at branch tips. Leaf margins plane throughout or narrowly incurved near leaf base and plane elsewhere, nearly entire near base, faintly serrulate at midleaf, apex coarsely dentate; costa absent or very faint, approximately 1/10 to 1/6 of leaf length. Laminal cells (measured from stem leaves) smooth, elongate, oblong to linear, upper and median ones 20–40 × 5–8 μm, basal 25–55 × 3–6 μm, cell walls strongly incrassate and porose throughout lamina; marginal leaf cells shorter, oblong to rectangular, with more solid walls; cells at leaf insertion shorter and wider than laminal cells, more strongly incrassate and porose, yellowish; alar cells numerous and forming distinct groups, short-rectangular to quadrate or oblate, with nearly solid walls. Branch primordia covered with embryonic leaves; pseudoparaphyllia few, to 0.15 mm long, mostly ligulate, biseriate. Gametoecia and sporophytes unknown.

Neckera praetermissa is characterized and distinguished by the following combination of characters: small size of plants; virtually symmetric leaves; walls of laminal cells strongly incrassate and porose; paraphyllia absent; costa very short or absent; and margins near leaf tips coarsely dentate. There are several species of Neckera s. l. in China and elsewhere in SE Asia that have one or some of these characters, but so far none with all of them (cf. Wu 2011, Enroth 2012 and the key therein). The closest match is N. undulatifolia (Tix.) Enroth (1992: 249) from northern Vietnam and southern China (Guangxi, Guizhou), but it has a much larger stature, having up to 10 cm long stems, and a long costa, as described and illustrated by Enroth (1992: fig. 1) and Wu (2011: plate 381, fig. 14–18). The two species in the region that have incrassate and porose walls of laminal cells and a relatively short and weak costa are N. denigricans Enroth (1996: 1) from northern Vietnam and Yunnan and the Sichuan endemic N. laevidens Wu & Jia (2011: 20) . Those species however have complanately foliate fronds distinctly different from those of N. praetermissa (cf. Fig. 1 View FIGURE 1 and 2 View FIGURE 2 ), asymmetric leaves and much more weakly toothed (denticulate or serrulate) upper leaf margins.

Neckera praetermissa was collected from the bark high up in the canopy of an unspecified tree species (“ad corticem arborum cacuminis altissimis”) at the elevation of 600 m a.s.l. in Cuc Phuong National Park, c. 80 km SSW of Hanoi. It may be a sun epiphyte tolerant of direct sunlight. Canopy epiphyte communities in the tropics are still poorly understood because they are not easily accessible and their species are mostly collected from twigs or branches that have fallen down from the tree canopy.