Chingia

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 31-32

CHINGIA

Chingia Holttum, Blumea 19:31. 1971.— TYPE: Chingia ferox (Blume) Holttum [= Aspidium ferox Blume ]

For complete synonymy, see Holttum (1974b, 1977b, 1982).

Etymology.— Named in honor of Chinese pteridologist Ren Chang Ching (1898–1986), who published extensively on the ferns of China and developed the first modern classification for Old World Thelypteridaceae .

Plants terrestrial, of open sites, with tree-fern habit, reaching heights of 5 m, though plants under 1 m tall may be fertile; rhizomes erect and caulescent, to 10 cm thick or greater, trunks to 1 m tall, stipe bases persistent; fronds monomorphic, erect, arching or spreading from caudex, usually pinnate-pinnatifid to pinnate-pinnatisect, rarely ( C. marattioides ) bipinnate; stipes stramineous to castaneous, with flat to terete scales, or hairs and scales; stipe scales proximally dense, thick, stiff, setiferous, dark brown to blackish, linear-lanceolate, to 2 cm long, transitioning to spreading, terete, spine-like scales distally, sometimes scales extending onto rachises, often breaking, leaving darkened stump-like scars, sometimes containing foul-smelling, irritating liquid ( C. urens , C. malodora ); blades chartaceous, drying green or reddish, ovate to lanceolate, proximally lacking greatly reduced or glanduliform proximal pinnae, with apex gradually reduced or conform, pinnae generally not greatly reduced distally, proliferous buds lacking; pinnae sessile or shortpetiolulate, with bases truncate, rounded, or broadly cuneate, not or little dilated at the base, margins dentate to deeply lobed, with prominent sinus-membranes; veins of one or more pairs generally anastomosing below the sinus (free in C. pricei and C. marattioides ), with many more pairs running along sinus membrane, large individuals with> 30 pairs of veins per segment, basalmost veins often arising from costae; aerophores absent; indument abaxially of rachises, costae, veins, and laminar tissue between veins of long and/or short hyaline acicular hairs, sometimes with clear stipitate glands or sessile yellow spherical glands, the young fronds sometimes sticky with a spicy-smelling, irritating glandular exudate ( C. australis, Herbert 2006 ); indument adaxially primarily restricted to axes (rachises and costae), of hyaline acicular hairs; pustules absent; sori most often near costules, less commonly medial, discrete or coalescent, exindusiate or with small indusia; sporangia glabrous or with spherical yellow glands, stipitate glands, or setulae; spores nearly always black or dark brown, papillose, winged, or echinate ( C. marattioides, Tryon & Lugardon 1991 ; C. fijiensis, Patel et al. 2019a ); x = 36, two species counted, both diploids. No hybrids known.

Diagnosis.— As Holttum (1971, 1974b, 1977b, 1982) suggested, Plesioneuron is the closest relative of Chingia , and some species share the unusual stiff, terete stipe scales (otherwise unique in the family) and black to dark brown spores. Plesioneuron differs in having free veins, deeply pinnatisect pinnae, a tendency to be of much smaller stature, often creeping rhizomes, medial sori (vs. borne along costules), persistent indusia, pustular laminae, and swollen aerophores. Plesioneuron marattioides is here transferred to Chingia . This taxon differs from species in both genera in being fully bipinnate. However, with molecular evidence, it is nested within Chingia . Alston (1940:227) noted in his description of this species that it “seems allied to [ Chingia ] imponens ”, in spite of its free veins. Based on the description ( Takeuchi 2005) and on observation of images of the type ( A: both scanned specimens and photos of microscopic features, courtesy of A. V. Gilman), we believe a second species, described as Amphineuron lindleyi , should also be transferred to Chingia .

Biogeography and ecology.—The 25 species of Chingia are distributed throughout Malesia and the southeastern Pacific to elevations of 2000 m. One widespread species, C. longissima , extends eastward to the Caroline Islands, Society Islands, Solomon Islands, and Marquesas. They are largely absent from continental southeast Asia but reach Thailand and peninsular Malaysia. A single endangered endemic species, C. australis , reaches south to Queensland, Australia ( Holttum 1986).

Taxonomic and phylogenetic studies.—The genus was described and its constituent taxa delineated by Holttum (1971). No previous authors had recognized these species as belonging to a natural group. Although initially suspecting a close affinity with Mesophlebion ( Holttum 1971) , he later concluded that the resemblance to that genus was superficial (1974a, 1977b, 1982) and that Plesioneuron (which Holttum, 1975, segregated from Mesophlebion ) was the only close relative of Chingia . This conclusion is supported by the reciprocal monophyly and sister relationship of these two genera inferred from phylogenomic evidence (Fawcett et al. in press). Although this sister relationship generally has high support, some conflict exists among individual gene trees. Chingia plus Plesioneuron form the most highly nested clade within the chingioid (non-core christelloid) clade, which includes in descending order along a grade Menisciopsis , Grypothrix , Mesopteris s.l., with Glaphyropteridopsis inferred either as sister to the rest of the chingioid genera or diverging from the backbone node before them, sister to the chingioids plus a large christelloid clade ( Fig. 1 ). Although the monophyly of the chingioid clade, and crown nodes corresponding to each genus within it, are highly supported, support of backbone nodes is low, and uncertainty remains about the relationships of these genera to one other.

Notes.—Of the 18 species treated by Holttum (1982), eight were known only from the type, or the type and one other collection. Most species are narrowly restricted endemics, and further study may reveal that the current taxonomic concepts for widespread species, e.g., C. ferox and C. longissima , are too broad (e.g., see Game et al. 2018). Chingia species are often pioneers, dependent on disturbance and open habitats for their establishment, and their populations may be short-lived ( Herbert 2006). Their dynamic population structure, ruderal nature, and narrow ranges make them a challenging target for conservation efforts. Furthermore, due to their exceptionally large size, narrow ranges, remote habitats, and, in some cases, foul-smelling, irritating secondary chemistry, our understanding of Chingia is impeded both by lack of collections and paucity of complete specimens.

Figures

FIG. 1. A synoptical treeillustrating relationships among genera of Thelypteridaceae based on Fawcett et al.(in press).