Leptochilus mengsongensis M. X. Zhao, 2017

Leptochilus mengsongensis M. X. Zhao View in CoL , sp. nov. ( Figure 1 View FIGURE 1 ).

Type: — CHINA. Yunnan Province: Jinghong, Xishuangbanna Dai Autonomous Prefecture, Menglong Township, Bulong Nature Reserve , elev. 1650–1750 m, E 100°28’ / N 21°30’, on trees in the understory of moist tropical montane rain forest, 16 November 2012, M. X. Zhao, N. Geekiyanage K. Myo & D. R. Nurdiana BNR-MS-086, (holotype KUN! GoogleMaps ; isotypes SWFU! GoogleMaps ).

Diagnosis: — Leptochilus mengsongensis is most morphologically close to L. pedunculatus , especially the rare sori connate individuals mentioned in the descriptions of L. pedunculatus ( Nooteboom, 1997) , but the vague and crooked veins are different from the prominent and slightly curved veins of L. pedunculatus , and it has thinly leathery, but not herbaceous, fronds. Besides, the former has much shorter stipe, especially the fertile fronds. In order to detect the difference between L. mengsongensis and L. pedunculatus intrinsically, rbcL gene sequences of both species were analyzed by using BLAST tool of NCBI (https://blast.ncbi.nlm.nih.gov/Blast.cgi; Genbank accession number: KY963656). Our results showed that in 663 sites, 20 are different from L. pedunculatus , which convinced again it is different from morphologically similar species L. pedunculatus . From Leptochilus axillaris , L. mengsongensis is distinguishable by its densely set roots and separate sori, in contrast to the absence of roots on the climbing rhizome and acrostichoid arrangement of the sori in L. axillaris . A morphological comparison of the L. mengsongensis and the two most similar species is provided in Table 1 View TABLE 1 .

Description: —Herbs, terrestrial, climbing up to 2– 3 m. Rhizomes slender, 2.8–3.4 mm in diam., green, flattened in cross section, long creeping, with sparse peltate scales; scales dark brown, ovate-lanceolate, 0.5–2.5 mm long, 0.08–1 mm broad, margin entire to sparsely denticulate, apex acute, clathrate. Stipe stramineous. Fronds simple, slightly dimorphic, distantly spaced, thinly leathery, glabrous, slightly decurrent; margins slightly undulate, apex long acuminate. Sterile fronds: lanceolate, stipe (0.6) 1.8–3.8 (7.8) cm, 21.8–38.6 cm × 1.8–2.8 cm, widest at or below middle, rarely forked at apex. Veins anastomosing (venation terminology as defined in Nooteboom, 1997), primary veins prominent, secondary veins (connecting veins) often rather crooked and ill defined, forming 1 or 2 irregularly arranged areoles, free included veinlets often forked. Fertile fronds: narrowly lanceolate, stipe 3.0– 11.9 cm, 14.8–25.1 cm × 0.5–1 cm, Lateral veins prominent, rather crooked. Sori densely covering lower surface, separate, oblong to rhomboid, prominent, paraphyses absent, ranging from mid-vein to margin of lamina, in a single row between lateral veins. Indurate cells 13–14, spores hyaline to light brown, ellipsoid in polar view, kidney-shaped in equatorial view, aperture 1/4–3/4 of spore length; surface shallowly tuberculate, usually plane with abundant spherical deposits with short echinate elements ( Figure 2 View FIGURE 2 ).

Geographic Distribution: — China, Yunnan, Xishuangbanna, Bulong Nature Reserve (Mengsong Section).

Ecology: —Mostly climbing on trees or in the understory of moist tropical montane rain forest, about 1700 m above mean sea level.

IUCN Red List Category:— The population of Leptochilus mengsongensis covers an area of about two square kilometers. About 100 mature individuals (clones of the same individual excluded) were encountered in the field. Therefore, L. mengsongensis can be categorized as Critically Endangered (CR) according to the red-listing criteria of small population size and restricted geographical range (IUCN Red List of Threatened Species Version 12, 2016). More field assessments are recommended in similarly forested regions in southwestern China, Myanmar and Vietnam to verify the conservation status. Based on our detailed assessment of the community ecology of epiphytes in MS-BNR, conservation of host trees, especially larger ones, will be the key strategy to insure its survival (Zhao et. al. 2015).

Etymology: —The epithet mengsongensis refers to its locality, which is the location of the only known site for it.

Discussion:— Tryon & Lugardon (1991), using electron microscopy, reported the spores of Colysis and Leptochilus to be similarly short echinate, which is consistent with our observations in the present study. The spores of Leptochilus mengsongensis are ellipsoid in polar view and kidney shaped in equatorial view. The surface is shallowly tuberculate with spherical deposits and sparsely short echinate, which agrees with the spore ornamentations characteristic of Leptochilus (Nooteboom & Zhang 2013) . Judging from the shape of leaf and sori, Leptochilus mengsongensis is similar to some individuals of L. pedunculatus , and when sori is mature, the sori patches are connected to each other, forming an acrostichoid felt similar to L. axillaris . L. mengsongensis differs from L. pedunculatus in having much shorter stipe (fertile fronds), thinly leathery texture lamina, slightly dimorphic lamina, indistinct lateral veins and stable inherited traits of sori, and the main difference to L. axillaris is that L. mengsongensis has the characteristics of separate sori, glabrous fronds and absent of paraphyses. After comparing the macro- and micro-morphological characters with similar species of Leptochilus , we confirmed that L. mengsongensis in MS-BNR was undescribed. This conclusion was also supported by molecular comparison with other members of Leptochilus .

We endorse the point of view of Zhang et al. (2015) who, based on the molecular work of Kreier et al. (2008), concluded that microsoroid ferns are not monophyletic, but Leptochilus appears to represent a natural group. Leptochilus is the oldest legitimate generic name among microsoroid ferns.