Keywords: DNA barcoding, flora, Indochina, matK, rbcL, taxonomy
Eustigma Gardner & Champ. (Gardner 1849) is a small genus of the Hamamelidaceae, distinguished from other genera by small auriculate petals and the greatly enlarged stigma (Harms 1930; Zhang et al. 2003). Currently, three species are known in the genus: E. balansae Oliv., E. lenticellatum C.Y.Wu and E. oblongifolium Gardner & Champ., distributed in mainland China, Laos, Taiwan and Vietnam, among which E. balansae is the only species recorded in Vietnam (Tardieu 1965; Hsieh 1993; Hô 2003; Zhang et al. 2003; Newman et al. 2007).
From 2013 to 2014, as part of a collaborative programme to document the biodiversity and ecology of Southeast Asia, Kyushu University (FU) together with Institute of Tropical Biology, Vietnam (VNM) carried out botanical field surveys in Hon Ba Nature Reserve, in South Vietnam (Figure 1) and found a species of Eustigma that was distinct from any of the three known species. Here, we describe this plant as a new species, Eustigma honbaense H.Toyama, Tagane & V.S.Dang, and place the species within the wider generic context by providing an updated identification key to all known species of Eustigma. Our conclusion is based on observations of specimens in the herbaria, BKF, E, HN, K, KAG, KYO, L, P, TI, and VNM, and specimen images on the website of JSTOR Global Plants (https://plants.jstor.org/). We also provide DNA sequences of two DNA barcode regions; the partial genes for the large subunit ribulose-1,5-bisphosphate carboxylase oxygenase (rbcL) and maturase K (matK) (CBOL Plant Working Group 2009); established protocols were used to determine the sequences of these regions (Kress et al. 2009; Dunning and Savolainen 2010).
Eustigma honbaense H.Toyama, Tagane & V.S.Dang, sp. nov.
VIETNAM. Khanh Hoa Province, Hon Ba Nature Reserve, evergreen forest margin along streamside, 401 m alt., 12°06.57'N, 108°59.21'E (DDM), 14 July 2014, S. Tagane, H. Kanemitsu, V.S. Dang, H. Tran, X.N. Loi, N.D. Thach, N. Dinh & H.N.P. Hieu V1586 (holotype: KYO!; isotypes: FU!, VNM!, the herbarium of Hon Ba Nature Reserve!).
Figure 1. Eustigma honbaense H.Toyama, Tagane & V.S.Dang, sp. nov.
A capsule; B immature fruits (lateral view, longitudinal and transverse sections from left) C, axillary bud (ab), bud scale (bs), petiole (pt) and stipule (st) and uppermost branch (ub) D bracteole E fruiting branch F vein with stellate hair G young branch H stellate hair on bud. [A–H from Tagane et al. V1586, KYO. Drawn by H. Toyama.]
Figure 2. Eustigma honbaense H.Toyama, Tagane & V.S.Dang, sp. nov.
A branch with infructescence B fruits; C abaxial surface of leaf D young infructescence E lamina showing glabrous abaxial surface F seeds with a large hilum showing basal side on the placenta (upper), and apical side (lower). [A–D photographed on 14 July 2014, E & F from Tagane et al. V1586, KYO.]
Figure 3. Terminal and axillary bud of Eustigma honbaense H.Toyama, Tagane & V.S.Dang, sp. nov.
A terminal and axillary bud B schematic diagram of transverse section of Fig. 4A C axillary bud D schematic diagram of transverse section of Fig. 4C E elongated terminal and axillary shoot F grayscale image of Fig. 4E. Abbreviations are as follows: axillary bud (ab), apical meristem (am), axillary shoot (as), bud scale (bs), branch (br), leaf (lf), petiole (pt), stipule (st), terminal shoot (ts). [A & C photographed on 22 November 2014, E & F from Toyama et al. V1975, FU.]
Eustigma honbaense is named after the type locality, Hon Ba Nature Reserve.