Chingia tortuosa S.E.Fawc., C.W.Chen & A.R.Sm., 2021

Chingia tortuosa S.E.Fawc., C.W.Chen & A.R.Sm. View in CoL , sp. nov. — Fig. 1 View Fig , 2 View Fig

A newly recognized species of Chingia , distinctive in having tortuous stipe scales ( Fig.2b View Fig ), abaxial laminar indument of stipitate glands (but not hyaline acicular hairs) ( Fig. 2c View Fig ), and pinnae incised less than halfway to the costae ( Fig. 2d View Fig ). — Type: Cheng-Wei Chen, Tien-Chuan Hsu & Moffat Fanerii SITW 11087 (holo BSIP!;iso TAIF!498969, 498970, 498971, 498972, TNM!, UC!2048647) , Santa Cruz , Solomon Islands, Vanikoro , Banie Island, Ngarabu camp to end road stream,primary forest,riverside, S11°37'45.8" E166°53'18.5", 600 m elevation, 27 June 2016 GoogleMaps .

Etymology. Named for its distinctive tortuous stipe scales.

Plants terrestrial,> 1 m tall. Rhizomes stout, erect caudices> 2 cm thick, clothed in brown, tortuous scales ( Fig. 1d View Fig ). Fronds fasciculate, arching to erect, monomorphic ( Fig. 1c View Fig ). Stipes robust, to 8 mm thick, stramineous, proximally scaly, scales deciduous, leaving darkened, ovoid scars. Stipe scales brown, linear-lanceolate, thick, the largest to 10 by 0.5 mm, translu- cent, tortuous, bearing spreading to erect hyaline acicular hairs ( Fig. 2b View Fig ). Blades pinnate-pinnatifid, ovate, not decrescent or abruptly reduced proximally, gradually reduced distally to a conform (pinna-like) apex. Rachises stramineous, adaxially grooved, with scattered, darkened, ovoid, stump-like scale scars present abaxially throughout, glabrous proximally, glandular medially, and with a mix of spreading, hyaline acicular hairs and scattered clear, stalked and sessile glands distally. Pinnae 14–20 by c. 2 cm, spreading, truncate, lacking auricles, distally with narrowly winged pinna-stalks, apices gradually attenuate, with 25–40+ segments, these incised less than halfway to costae. Aerophores present as darkened swellings at pinna bases ( Fig. 1b View Fig ). Veins simple and pinnate, steeply angled from costae (c. 45°), 6–9 pairs per segment, usually with 1 or 2 pairs anastomosing below the sinus at a steep angle (<90°) to form an excurrent veinlet to a cartilaginous, elongate, adaxially concave sinus membrane ( Fig. 2d View Fig ). Indument adaxially of hyaline acicular hairs to 0.4 mm long, these primarily restricted to the costae, with a few scattered hairs on the veins. Indument abaxially of minute, stalked and sessile clear glands and sessile golden to amber coloured glands, hairs lacking. Sori oblong to round, borne adjacent to costae and costules, gradually decreasing in size toward segment apices, proximal sori slightly elongate along veins, indusia absent or vestigial. Sporangia bearing numerous minute, clear, sessile or shortstalked glands on capsule ( Fig. 2c View Fig ). Spores black.

Distribution — Known only from the type locality, Solomon Islands (Vanikoro) ( Fig. 1a View Fig ).

Habitat & Ecology — Recorded only from slopes along streams at c. 500 m ( Chen et al. 2017).

Vernacular name — ‘Vanikoro Chingia’, proposed here.

Conservation status — During our expedition, only a single population, with fewer than 100 individuals, was encountered. According to the criteria used by the IUCN red list ( IUCN 2012), this species should be assessed as Endangered based on its limited extent, which is restricted by island size (criterion C) and small population size (criterion D). Furthermore, Vanikoro has been the site of unsustainable logging for nearly 100 years ( Bennett 2000). As logging operations continue unchecked,

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both the quality and extent of primary forests on the islands is in rapid decline. Unfortunately, we are aware of no formal conservation policy that has been adopted to protect the rich and unique biodiversity of the island.

Notes — Based on the molecular phylogeny of Fawcett et al. (2020, in press), which included 14 Chingia accessions represented by 407 nuclear loci, the type of Chingia tortuosa is sister to a collection of C. clavipilosa Holttum ( Chen Wade 4658, UC 2072750) from Mount Kinabalu, the type locality of that species, with 100 % support, based on both maximum likelihood and coalescent analyses. The typical variety of C. clavipilosa shares the namesake stipitate glands (short, capitate hairs), but is easily distinguished from C. tortuosa by differences in indument. Chingia clavipilosa has abundant transparent spreading hairs on the pinna axes abaxially ( Fig. 2a View Fig ), in ad- dition to the stipitate glands; similar glands are present, but such hairs are lacking in C. tortuosa ( Fig. 2d View Fig ). Many species of Chingia have terete, spine-like scales (e.g., C. ferox ), while others have flattened scales, these usually thickened, stiff, and at most somewhat undulate, but not tortuous (but see Chingia tenerior Holttum, BS (Ramos) 33066, P (seen from photo), a Philippine endemic that may be distinguished from C. tortuosa by pinnae incised more than halfway to costae). In all species of Chingia examined, the deciduous stipe scales leave distinctive stump-like scars along the stipes and/or rachises.

Two additional species of Chingia occur on the Solomon Islands; these are C. malodora (Copel.) Holttum , and C. cf. longissima , both of which may be distinguished from C. tortuosa by their copious, erect, terete stipe scales. The stipe scales of C. malodora are noteworthy in emitting a foul odour when crushed ( Holttum 1974).