Cyrtomium calcis Liang Zhang, N.T.Lu & Li Bing Zhang, 2023

Lu, Ngan Thi, Wei, Hong-Jin, Vuong, Luong Dinh, Toan, Le Chi, Zhang, Li-Bing & Zhang, Liang, 2023, Cyrtomium calcis sp. nov. and six new records of the shield fern family (Dryopteridaceae) from Vietnam, Phytotaxa 583 (1), pp. 15-26 : 16-18

publication ID	https://doi.org/ 10.11646/phytotaxa.583.1.2
DOI	https://doi.org/10.5281/zenodo.7622249
persistent identifier	https://treatment.plazi.org/id/D90787F1-FFF0-1533-14EF-FC104D067EC0
treatment provided by	Plazi
scientific name	Cyrtomium calcis Liang Zhang, N.T.Lu & Li Bing Zhang
status	sp. nov.

Treatment

Cyrtomium calcis Liang Zhang, N.T.Lu & Li Bing Zhang View in CoL , sp. nov., Fig. 1 View FIGURE 1

Type :— VIETNAM. Hagiang Province : Vi Xuyen District , Tung Ba Community , Du Gia National Park (Khau Ca Nature Reserve), Hom Mountain, 22°50’40’’N, 105°07’47’’E, elev. ca. 1150 m, on the top of limestone mountain, 13 December 2013, Li Bing Zhang, Liang Zhang & Ngan T. Lu 6932 (holotype VNMN!; isotypes CDBI!, MO!) GoogleMaps .

Diagnosis: This species is most similar to Cyrtomium pachyphyllum ( Rosenstock 1914: 130) C.Christensen (1917: 11) in having erect rhizomes, dense, concolorous, and fimbriate-dentate scales throughout fronds, leathery lamina, ovate pinnae, and dentate indusia, but the new species has ovate scales on stipe base (vs. lanceolate scales in C. pachyphyllum ), lanceolate-oblong lamina (vs. oblong lamina in C. pachyphyllum ), up to 14 pairs of pinnae (vs. often 1–5 pairs in C. pachyphyllum ), lowest pinnae shorter than the middle ones (vs. similar in C. pachyphyllum ), fewer rows of areolae (2–(4)) in venation structure (vs. up to 5 rows of areolae in C. pachyphyllum ).

Plants terrestrial, perennial, evergreen. Rhizome erect, densely covered with ovate, lanceolate, linear, brown scales. Stipe stramineous, 15 cm long, 1–3 mm in diam., base densely scaly, scales membranous, concolorous, reddish-brown, ovate, lanceolate or linear (6–20 × 0.3–4.4 mm), fimbriate-dentate, apex long acuminate or slight twist; upward densely scaly, scales brown, narrow lanceolate, linear (2.5–6.0 × 0.1–0.7 mm). Lamina 1-imparipinnate, lanceolate-oblong (13–23 × 1.9 cm), base cordate to hastate, apex acute to slight acuminate, thick leathery; rachis ca. 1.5 mm in diam. with dense scales abaxially and adaxially, scales similar to scales on distal stipe but smaller (1–1.5 × 0.05–0.5 mm); pinnae alternate, 9 to 14 pairs, short-stalked or nearly sessile, ovate (1.5–3.5 × 1.2–1.9 cm), both adaxial and abaxial sides with microscales, glossy adaxially, margin entire, acroscopic base auriculate, blunt auricle, auricle overlap each other, apex acute; lowest pinnae shorter than middle ones, upper pinnae ovate, up to 3.5 × 1.9 cm; terminal pinna deltoid-ovate (1.5–2.5 cm); venation pinnate, obscure, veinlets form 2, 3, rarely to 4 rows of areola, each areolae with 1 included veinlet. Sori rounded (ca. 1.5 mm in diam.), 1–25 or more per pinna, 1 or 2(–3) rows on each side of midrib; indusia orbicular (1.3–1.9 mm in diam.), dentate; spores large, ellipsoid (54–60.6 µm in diam.), inflated tuberculate folds, plain exospore.

Etymology:— The specific epithet, calcis , is formed from the Latin word calcis , relating to lime. It refers to the limestone habitat of this new species.

Geographical distribution and habitat:— Types were collected from a limestone peak in primary evergreen broad-leaved forests in Khau Ca Nature Reserve, Vi Xuyen District, Hagiang Province. Community is composed of some taxa accompanying the new species as Cyrtomium hemionitis Christ (1910: 138) , Polystichum minimum (Y.T. Hsieh 1989: 17) Li Bing Zhang (2012: 58) , P. auriculum Ching (1949: 309) , an Ericaceae , a Lauraceae , and an Orchidaceae . Two small populations of the new species were also found in Guangxi, China.

Provisional conservation status:— Only a few mature individuals of Cyrtomium calcis were seen in the type locality although a few field investigations have been conducted by Vietnamese colleagues and the first author since 2013. Two populations in Guangxi, China were quite small and the three localities in China and Vietnam are only about 92 km in air distance. Based on current information and following the IUCN Guidelines ( IUCN 2022), the new species is temporarily assessed as Critically Endangered C 2a (i, ii).

Additional material examined:— CHINA. Guangxi: Napo County, elev. ca, 1300 m, 17 June 1982, Ding Fang, Mao-Xiang Lai & Zhen-Gang Wang 25384 (GXMI); elev. ca. 1250 m, 17 July 1985, Ding Fang & De-Hai Tan 79661 (GXMI). Tianlin County , elev. ca. 1490 m, 29 January 2016, S.L. Jin JSL3613 (CSH, paratype) .

Notes:— Cyrtomium calcis is endemic to the limestone areas, but it is not closely related to other species endemic to limestone areas, e.g., C. hemionitis , C. nephrolepioides ( Christ 1902: 258) Copeland (1929: 136) , C. pachyphyllum , and C. shingianum H.S.Kung & P.S.Wang (1997: 23) , as shown in our phylogenetic tree ( Fig. 2 View FIGURE 2 ). The phylogenetic relationships of C. calcis are quite isolated and it is resolved as one of the earliest diverging lineages. Therefore, the discovery of C. calcis is quite significant in studying the phylogeny and evolution of the genus.

Morphologically, the limestone species of Cyrtomium share a distinct morphological feature, the presence of the cordate pinna base (except C. chingianum P.S.Wang 1997: 24 ) ( Lu & Cheng 2003, Zhang & Barrington 2013) and the new species bears gross morphological features that are consistent with those in other limestone species, e.g., thicker pinna texture, fewer pairs of pinnae per frond, broader pinnae, and more rows of areolae in venation structure ( Mitsuta 1977, Lu & Cheng 2003, Zhang & Barrington 2013). The fact that C. calcis is not closely related with other limestone species in the genus suggests that these morphological similarities are homoplasious.

The discovery of Cyrtomium calcis is also contribution to the limestone flora in northern Vietnam that is currently not well understood (e.g., Lu et al. 2014, also see below).