Eustigma honbaense H.Toyama, Tagane & V.S.Dang, 2016

Toyama, Hironori, Tagane, Shuichiro, Dang, Van Son, Tran, Hop, Nagamasu, Hidetoshi, Naiki, Akiyo & Yahara, Tetsukazu, 2016, A new species of Eustigma (Hamamelidaceae) from Hon Ba Nature Reserve, Vietnam, PhytoKeys 65, pp. 47-55 : 49-51

Eustigma honbaense H.Toyama, Tagane & V.S.Dang sp. nov. Figs 2 , 3 , 4

Diagnosis.

This species is similar to Eustigma oblongifolium Gardner & Champ., but distinguished from that species by having entire elliptic to oblong leaves (vs. partly dentate oblong-lanceolate leaves), infructescences 5-10.3 cm long (vs. 3-5 cm long), apical part (above tepal scar) of capsules 6.5-9 mm long (vs. 3-5 mm long) and seed hilum 4 mm long and 3 mm wide for bigger side (vs. 2-3 mm long and 1-1.5 mm wide).

Type.

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 !) .

Description.

Trees 8-10 m tall. Branches yellow-green when young, turning brown when mature; indumentum sparsely to densely brown stellate hairy when young (denser on the uppermost branch), glabrescent; lenticels more distinct on young branches when dry. Terminal buds naked, narrowly ovoid, ca. 5 mm long, ca. 2 mm wide, having 2 opposite stipules incompletely covering young leaves, linear, ca. 4.5 mm long, ca. 0.5 mm wide, brown stellate hairy. Axillary buds scaled, narrowly ovoid, ca. 3.5 mm long, ca. 1.2 mm wide; bud scales 2, opposite, incompletely covering young leaves, narrowly ovate-oblong, 3-4 mm long, 0.5-1 mm wide, densely brown stellate hairy. Leaf blades elliptic to oblong, 6.5-21.5 cm long, 2.2-8.5 cm wide, coriaceous, lustrous and glabrous on both surfaces except veins below, base obtuse to cuneate, apex acuminate to rounded, margin entire; midribs sunken and glabrous above, prominent and sparsely brown stellate hairy below; secondary veins 5-9 pairs, slightly sunken and glabrous above, prominent and sparsely brown stellate hairy below; tertiary veins reticulate, slightly sunken and glabrous above, prominent and sparsely brown stellate hairy below; petiole 9-14 mm long, sparsely brown stellate hairy; stipules 2, opposite, caducous, linear, 5-8 mm long, 0.5-1 mm wide, brown stellate hairy. Flowers not seen. Infructescences terminal and axillary, racemose, 5-10.3 cm long; peduncles 1.2-4.5 cm long, brown stellate hairy, with 0-2 basal leaves; basal bracts not seen; bracts and bracteoles caducous, narrowly ovate, 1.8-3 mm long, 0.5-1 mm wide (but see note), densely brown stellate hairy; fruiting pedicels 5-8 mm long, densely brown stellate hairy. Floral cups in young fruits, turbinate, 2-3 mm in diameter, densely brown stellate hairy; ovary 2-locular; ovules 1 per locule. Capsules ovoid-globular, 12-16 mm long, 9-10 mm in diameter, woody, dehiscing loculicidally by two 2-lobed valves, sparsely lenticellate, sparsely brown stellate hairy, the length above tepal scar 6.5 -9 mm; endocarp loose from woody exocarp. Seeds 2 per capsule, narrowly ovoid, ca. 10 mm long, ca. 4.5 mm wide, ca. 3 mm thick, brownish black, smooth, hilum ca. 4 mm long, ca. 3 mm wide for bigger side (the basal side on the placenta).

Other specimen examined.

VIETNAM. Khanh Hoa Province, Hon Ba Nature Reserve, evergreen forest margin along streamside, 393 m alt., 12°06.51'N, 108°59.26'E (DDM), 22 November 2014, H. Toyama, S. Tagane, V.S. Dang, H. Nagamasu, A. Naiki, H. Tran, C.J. Yang, H.Q. Cuong & H.N.P. Hieu V1975 (FU!, VNM!, the herbarium of Hon Ba Nature Reserve!).

Distribution and habit.

This species is only known from Hon Ba Nature Reserve of southern Vietnam. We found only three individuals in the evergreen forest along a stream at ca. 400 m alt. The flora of this area is reported in Choudhary et al. (2012), Schuiteman et al. (2013) and Tagane et al. (2015a, b).

Phenology.

Flowering season is unknown. Immature fruits and capsules were observed in July and November.

Etymology.

Eustigma honbaense is named after the type locality, Hon Ba Nature Reserve.

Preliminary conservation status.

Eustigma honbaense was collected from a single locality in the Hon Ba Nature Reserve, where only three individuals (one reproductive tree and two young trees) were found in evergreen forest along a streamside. The forest around the habitat was frequently logged and disturbed. Therefore, this species is assessed as Critically Endangered (CR) using the criterion D of the Red List Categories ( IUCN 2012), although more individuals could be discovered by more thorough surveys.

Note.

Eustigma honbaense has terminal naked buds and axillary scaled buds that are in contrast with the description of Eustigma having naked-buds as given in the Flora of China ( Zhang et al. 2003). The naked bud is covered either with immature leaves that develop to foliage leaves or with their stipules, while the scaled bud is covered with cataphylls or stipules that are highly modified to protect the shoot tip ( Nitta and Ohsawa 1998). The terminal buds of Eustigma honbaense are classified as naked buds because they are incompletely covered by 2 stipules (Fig. 4A, B, E & F ), while the axillary buds are classified as scaled buds because they are covered by 2 cataphylls that are subsequently shed or remained at the tip of previous shoot without further growth (Fig. 4C, D, E & F ). The terminal bud of Fig. 4B shows alternate leaf arrangement from the axillary bud, but same direction is also observed.

The description of bracts and bracteoles is insufficient because most of the bracts and bracteoles had been shed. Eustigma oblongifolium and Eustigma lenticellatum have 3-bracteate flowers ( Gardner 1849; Hsieh 1993; Wu 1977), while Eustigma balansae has 2-bracteate flowers ( Oliver 1891; Tardieu 1965). This could be a key trait to distinguish between species. Further collections of Eustigma honbaense are needed.

The matK sequences between Eustigma honbaense and Eustigma oblongifolium (AF013043) differ in 6 bases of the 781 total. The rbcL and matK sequences between Eustigma honbaense and Eustigma balansae (rbcL: HQ415214, matK: HQ415379) differ in 1 base of the 517 total and 5 bases of the 761 total, respectively.

Genebank accession No.

Tagane et al. V1586: LC005200 (rbcL), LC005201 (matK).

Figures

Figure 2. 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. V 1586, KYO. Drawn by H. Toyama.]

Figure 3. 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. V 1586, KYO.]

Figure 4. 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. 4 A C axillary bud D schematic diagram of transverse section of Fig. 4 C E elongated terminal and axillary shoot F grayscale image of Fig. 4 E. 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. V 1975, FU.]