Zingiber chengii (Zingiberaceae), a new species from Taiwan

Abstract In this article, we describe a new species, Zingiber chengii Y.H. Tseng, C.M. Wang & Y.C. Lin, discovered on a rock cliff of Youluo riverside in northern Taiwan. This species is easily distinguished from other known congeners by its grass-like leaves, spikes composed of a few sterile bracts, and seeds one-third enveloped by the aril. Color illustrations, line drawings, and a key to species of Zingiber in Taiwan are provided as well as comparative morphology in relation to its allied species, geographical distribution, and conservation status.


Introduction
Zingiber Mill (Zingiberaceae) comprises approximately 100−150 species, with its center of diversity in Southeast Asia (Wang 2000, Wu and Larsen 2000, Theerakulpisut et al. 2012. Zingiber spp. are mostly perennial herbs, characterized by a pulvinus leaf base (a swollen part of the petiole) and a horn-shaped anther crest embracing the up-per part of the style (Bai et al. 2015a). Several species in this genus are known to be widely cultivated in tropical Asia, such as Z. officinale Roscoe and Z. zerumbet (L.) Sm., and carry great economic value (Wang 2000). The genus Zingiber is divided into Z. sect. Zingiber, sect. Dymczewiczia (Horan.) Benth., sect. Pleuranthesis Benth., and sect. Cryptanthium Horan. based on the position of the inflorescence (Schumann 1904). Additionally, species of the sections Zingiber and Dymczewiczia have spherical pollen grains with cerebroid sculpturing, while those belonging to the sect. Cryptanthium have ellipsoidal pollen grains with spiro-striate sculpturing (Theilade et al. 1993).
Three native species of Zingiber have been recognized by Wang (2000) in Taiwan, i.e. Z. kawagoii Hayata, Z. oligophyllum K.Schum and the insufficiently studied Z. pleiostachyum K. Schum. Subsequently, Z. shuanglongense C.L.Yeh & S.W.Chung were described from central to southern Taiwan (Yeh et al. 2012). All four Taiwanese species belong to sect. Cryptanthium.
Recently, we discovered an unknown Zingiber in northern Taiwan belonging to the Z. sect. Cryptanthium, as indicated by the radical inflorescences with a procumbent peduncle. Here, we describe this new species of Zingiber and evaluate its conservation rank.

Materials and methods
An unknown species of Zingiber was found abundant on a rock cliff of Youluo riverside, where more than 100 individuals were observed in an area of ca. 400 m 2 (24.694, 121.184). In addition, more than 50 individuals were discovered in similar habitat along the same riverside (24.695, 121.220). Morphological measurements were made from both herbarium and spirit samples by a ruler and digital calipers. For morphological descriptions, the terminology used by Beentje (2012) and Leong-Škorničková et al. (2014) was followed.
Protologues of Zingiber spp. and herbarium specimens were examined, including type specimens deposited in HAST, IBSC, NTNU, TAI, TAIF, TCF, TI, TNM, and PPI, in addition to specimens at K, UPS, and US, which were available as images. Considering the similarity of the newly collected species and Z. tenuifolium L. Bai, Škorničk. & N.H. Xia, we also compared the Taiwanese species with Z. tenuifolium, as described by Bai et al. (2015b).
The conservation rank for the new species was evaluated according to IUCN (2017). Pollen grains for scanning microscope examination (voucher: Z. chengii Hsinchu County, Jianshih Township, Y.C. Lin 1116& 1148 were prepared following Halbritter (1998): anthers were treated with DMP (2, 2-Dimethoxypropane) for 30 minutes and transferred to acetone for 30 minutes and critical-point dried. The material was mounted on a stub and sputter coated with gold (Quorum SC7620) and examined using a Hitachi S-3400N microscope.
A distribution map was generated by using QGIS ver. 3.4 from package of Lin (2018). Diagnosis. Zingiber chengii sp. nov. is morphologically similar to its Taiwanese congeners. However, the new species can be distinguished from them by its deciduous leafy shoots while those of Z. kawagoii, Z. oligophyllum and Z. shuanglongense are evergreen; Z. chengii has narrow lanceolate to linear leaves, whereas Z. kawagoi and Z. shuanglongense have ovate to lanceolate ones; except Z. oligophyllum, which has yellow flowers, all native species of Taiwan have reddish-purple flowers; each spike of Z. chengii bears 1−3 flowers, whereas spikes of Z. kawagoi and Z. shuanglongense bear 8−11 and 4−10 flowers, respectively; Zingiber chengii rarely has sterile bracts, whereas Z. kawagoii and Z. shuanglongense have apparent sterile bracts; Zingiber chengii has ovoid fruit, whereas Z. kawagoii and Z. shuanglongense has ellipsoidal one. Both Z. kawagoii and Z. shuanglongense are almost enveloped by the aril, whereas Z. chengii is one-third enveloped by the aril (Table 1).
Compared with the images of the syntype of Z. pleiostachyum, Z. chengii has much narrower lamina, with a length: width ratio of ca. 6 (vs. ca. 3.8 in Z. pleiostachyum) and rarely has sterile bracts. Zingiber chengii is similar to Z. tenuifolium L. Bai endemic to Yunnan (Bai et al. 2015b), but the number of blades per leafy shoot of Z. chengii is about 11-15 vs. 13-23 in Z. tenuifolium. The two species can also be distinguished by the length to width ratio of the lamina, which is ca. 6 in Z. chengii vs. ca. 10 in Z. tenuifolium. Zingiber tenuifolium also has apparent sterile bracts while these are rare in Z. chengii. These comparisons indicate that Z. chengii is clearly different from other known similar congeners, therefore we treat Z. chengii as a new species in Taiwan. Also, Z. chengii has ellipsoidal pollen grains with spiro-striate sculpturing (Fig. 5), and the inflorescence borne on a radical, procumbent peduncle ( Fig. 1A, 2E, 3F). These characters indicate that this new species belongs to sect. Cryptanthium.
Phenology. Flowering between May and July, and fruiting between July and September. Growth and reproduction period between March and September, withering from September to November, and dormant period between December and February (Fig. 2).
Distribution and habitat. Endemic species of Taiwan. Based on the geographical climatic regions and vegetation zones (Su 1984(Su , 1985, Z. chengii is distributed only in the northwest inland region, moist areas of cloud forests of the Machilus-Castanopsis forest zone at an altitude of 530 m, and is found only on the rock cliff of Yuluo riverside (Hsinchu County) in northern Taiwan (Fig. 4) podiaceae). Sometimes, Z. kawagoii is found nearby; however, no potential hybrid individual has been observed.
Conservation status. Zingiber chengii has been abundant on the rock cliff of Youluo riverside, where more than 100 individuals have been observed in an area of ca. 400 m 2 , since 2014. However, its population gradually decreased due to disturbances by visitors. Additional specimens were discovered along the Yuluo riverside in similar riverine habitats. These areas are difficult to approach due to the presence of hazardous rivers and cliffs. We categorize the new species as Endangered (EN B1; C2a(i)) following IUCN (2017) Identification key to the species of Zingiber in Taiwan