Monoon vietnamensis (Annonaceae), a new species from central Vietnam

Ngọc-Sâm Lý
Department of Biological Resources, Institute of Tropical Biology, Vietnam Academy of Science and Technology, 85 Tran Quoc Toan Road, District 3, Hochiminh City, Vietnam (e-mail: samly@itb. ac.vn)
Received 9 Jan. 2017, final version received 20 Mar. 2017, accepted 21 Mar. 2017

Monoon vietnamensis N.s. Lý, a new species of Annonaceae, is described and illustrated from Mount D'au, Quảng Ngãi Province, central Vietnam. It is morphologically similar to M. bornensis and M. anomalum, but differs by much larger and oblong- elliptic to obovate-elliptic leaves, with 12-14(16) pairs of nerves and a cuneate leaf base; much longer and narrowly ovate to linear ovate petals, with sparsely scattered short hairs outside; inner petals slightly longer than the outer petals; and much longer fruiting pedicels. A key to the species of Monoon in Vietnam is provided.\

The genus Monoon (1865) belongs to the tribe Miliuseae in the family Annonaceae (Mols et at. 2004,2008, Chatrou et at. 2012, Xue et al. 2012). It consists of at least 60 species of trees distributed in tropical Asia, ranging from India to Japan and Australia (Turner 2013). Monoon was established by Miquel (1865) and is characterized by the single and basal ovule per carpel. Some of the 18 species Miquel originally accommodated in Monoon are currently placed in Desrnos, Friesodielsia, Huberantha, Man si a, Marsypope- talum, Phaeanthus, Polyalthia s. stricto or Spha- erocoryne (Mols et at. 2008, Saunders et at. 2011, Xue et al. 2012, Chaowasku et at. 2015). Bentham and Hooker (1867) reduced Monoon into one of two sections they recognized within Polyalthia, but Huber (1985) recognized three informal groups, Longifolia, Korinti and Suberosa. Recent phylogenetic studies based on morphological and molecular data have suggested a reinstatement of the generic level of Monoon. In the new circumscription it contains also species previously placed in CJeistopetalum, Enicosan- thum, and Woodiellantha (Mols et al. 2008, Xue et al. 2012). Currently Monoon is defined by its eucamptodromous leaf venation, decurrent insertion of secondary nerves, and uniovulate carpels (Xue at al. 2012). In Vietnam, there are at least eight species currently placed in Monoon, some of them earlier recognized in Enicosanthum and Polyalthia (Bân 1974, 2000, Hộ 2003, Xue et al. 2012).

Recent floristic explorations on Mount D'au in 2015-2016, a community forest of Khánh Giang-Trường Lệ Villages, Nghĩa Hành District, Quảng Ngãi Province, central Vietnam, led to the discovery and collection of interesting specimens of a Monoon. The species is cauli- florous, with the flowers growing from woody tubercles on the trunk. Critical examination of the flowering and fruiting materials, and comparison of type material and protologues of closely related species from neighbouring countries (e.g. King 1893, Merrill 1915, Any-Shaw 1939, Sinclair 1951, 1955, Bcân 1974, 2000), revealed that the specimens did not match any hitherto known species, and I therefore consider it to be a species new to science.

All measurements and descriptions were made from mature living plants, material preserved in 70% ethanol, and herbarium collections. Type specimens of the morphologically most closely related species were examined and/ or accessed as high-resolution digital images from HN, K, P, SING, and VNM (herbarium codes follow Index Herbariorum (http://sweet- gum.nybg.org/science/ili/). All morphological characters were described using the general terminology by Beentje (2012) and standard works of Airy-Shaw (1939), Sinclair (1951, 1955) and Turner (2013).

Monoon vietnamensis N.s. Lý, sp. nova (Fig. 1)
Type: Vietnam. Quảng Ngãi Province, Nghĩa Hành District, Hành Tín Đông Commune, Trường Lệ Village, Mount Dầu, Đá Bông hill, 14°52'0.62"N, 108o48'7.74''E, elev. 324 m a.s.l., 5 May 2016 Ngọc-Sắm Lý, Lý-670 (holotype VNM; isotypes P, VNM). — Paratypes: Same locality, 10 August 2015 Ngọc-Sôm Lý, Lý-730 (VNM); same locality, Nhự hill, 14°52T).62"N, 108°48'7.74"E, elev. 324 m a.s.l., 10 April 2015 Ngọc-Sâm Lý, Lý-597 (VNM), 9 August 2015 Ngọc Sâm Lý, Lý-668 (VNM).

Monopodial evergreen trees with horizontal branches, 10-15 m tall, 10-25 cm dbh; bark densely lenticellate, dark brown to back brown with olive-greenish patches, reddish-brown when peeled off. Terminal twigs 4-7 mm in diam., longitudinally wrinkled or somewhat ridged, occasionally sparsely pale lenticellate, dark brown to grey-brown, glabrous when older, youngest twigs generally with short pubescence. Leaves coriaceous, oblong-elliptic to obovate- elliptic, (25)28-37 X 7.5-13.5 cm, adaxially dark green, shiny, abaxially green, drying greenish- grey or brownish-grey above and dull brownish-yellow below, glabrous except sparse pale hairs on midrib and secondary veins below, apex shortly acuminate, base cuneate and symmetrical; midrib slightly sunken above, prominent below with longitudinal furrows along midrib abaxially; secondary veins 12-14(16) per side, arching and looping indistinctly near margin, more or less flush above, prominent below, insertion on midrib decurrent; tertiary venation scalariform. Petioles stout, shallowly canalicu- lated adaxially, 7-12 nun long, 4-6 nun long thick, dull greenish, drying dark brown to black- brown, shortly pubescent then glabrous with age, irregularly and finely wrinkled. Inflorescences cauliflorous on woody tubercles on trunk, particularly near base, 2^1-flowered cymes arising from shortly branched leafless twigs; branched leafless twigs 0.5-3.5 cm long, 3-5 mm diam. Flowers faintly malodorous; flowering pedicels 2.5-9.3 cm long, cylindrical and 1-3 nun thick at mid-point, widening and angular distally, 2-4 nun at widest point, light green, covered with shortly adpressed white hairs, usually one medial bract at middle point of pedicel; bracts triangular-ovate, 1-3 x 3-4 nun, light green, abaxial surface densely short pale pubescent, glabrous within, apex acute; sepals valvate, reflexing, broadly triangular, 2.5-5 x 5-10 mm, green, drying brown-black, abaxial surface densely short pubescent, glabrous within, apex acute; petals in two whorls of 3, valvate, thick and fleshy, narrowly ovate to linear-ovate, pure white with bnght green at base, inconspicuously channeled at center, margins somewhat mrolled, inconspicuously veined near base, base truncate, apex acute; outer petals 3.7-9.2 x 0.7- 1.3 cm, abaxial surface with sparse scattering of short hairs, glabrescent at apex and edges; inner petals slightly longer than outer petals, 3.8- 10.8 x 0.6-1.4 cm, abaxial surface very sparsely hairy, glabrescent at apex; stamens 86-142 per flower, in 4 or 5 whorls, 1-1.3 mm long, glabrous; filaments ca. 1/5 length of entire stamens, pale greenish; anthers 0.5-0.7 nun long, tinged white-greenish; connectives ca. 0.2 mm thick, hexagonal, pale purplish, apex truncate or somewhat convex, glabrous; carpels 48-62 per flower, with one basal ovule in each, caipel 1-1.5 nun long, angular-cylindrical, pale greenish, densely hairy with brown hairs; stigmas connivent, capitate, 0.4-0.5 mm diam., pale greenish, densely hairy with brown hairs, abscising after anthesis; torus pentagonal, somewhat convex, 6-7 nun diam., pale cream, with scattered pale hairs sur-rounding stamens and carpels. Fruit composed of (1)12-30(35) stipitate monocarps, borne on a woody pedicel, 1.5-3.5 cm long, 4-6 nun diam. at mid-point; sepals caducous; fruiting torus globose, up to ca. 5 cm diam., grey or grey- brown, glabrous; monocarps light green when young, purple-red tinged when mature and turning dark red-purple when ripe, ripe monocarps oblong-ovoid, 4.3-5 x 2.3-2.5 cm, drying black, smooth, shiny, glabrous, apex rounded; fruiting walls 2.5-4 mm thick; stipe 2-4.5 cm long, 3.4-5 mm thick at mid-point, densely hairy with minute hairs, becoming glabrous. Seed 1 per monocarp, 1.7-2.2 x 0.8-0.9 cm, white, shiny, drying brown, with a distinct longitudinal circumferential groove, with ruminations in cross- section, endosperm lamelhform, soft. Flowering in May-June, fruiting in June-September.

Monoon vietnamensis
Fig-1. Monoon vietnamensis (from the holotype). — A: Plant In natural habit. — B: Inflorescences on main trunk. — C: Infructescences on main trunk. — D: Twig. — E: Detail of cymes on woody tubercles. — F: Inflorescence close to base of trunk. — G: Top view of flower. — H: Side view of flower. — I: Old branch with mature leaves. — J: Lower view of sepals. — K, and K2: Top and side views of stamens and carpels. — L: Side view of torus showing sepals, stamens and carpels. — M: Top view of carpels, torus after anthesis. — N: Petals: N1 -outer, N2-inner. — O: Close-up of carpels (alcohol materials). — P: Close-up of stamens (alcohol materials). — Q: Detail of infructes- cence. — R: Fruit (longitudinal-section). — S. Seed (longitudinal-section). — Scale bars: 10 mm for J, Kv K2, Land M; 1 mm for O and P; 1 cm for R and S.

Distribution, habitat and uses: So far M. vietnamensis is known only from the type locality, where fewer than 100 scattered mature flowering and/or fruiting individuals are known around Mount D'äu. For this reason, this species can be considered as locally abundant and treated as an endemic species. It grows near stream banks, under forest canopy or shaded areas on steep slopes composed of eroded sandstone in secondary evergreen broad-leaved forest dominated by dipterocaps, at 130-270 m a.s.l. Monoon vietnamensis is harvested by local people for firewood, charcoal, and pole wood.

Monoon vietnamensis is most similar to M. bornensis (East Kalimantan, Borneo, Indonesia) and M. anomahan (West Sumatra, Indonesia) m habit and reproductive characters, with cauhflor- ous, solitary flowers or few-flowered cymes arising from woody tubercles on the main trunk. It differs markedly from both, however, in having much larger, oblong-elliptic to obovate-elliptic leaves, (25)28-37 x 7.5-13.5 cm (oblong, 7-9 x 3-4 cm in M. borneensis; elliptic-oblong, 13.9- 21.5 x 4.5-6.2 cm in M. anomalum). The leaf lamina of M. vietnamensis has 12-14(16) pairs of nerves (8-9 pairs in M. borneensis, 7-8 pairs in M. anomalum), and with a cuneate leaf base (rounded in M. borneensis, attenuate to rounded in M. anomalum). The petals of M. vietnamensis are furthermore much longer (3.8-10.8 x 0.6-1.4 cm), narrowly ovate to linear ovate, with sparse scattering of short hairs on abaxial surface; M. borneensis, in contrast, has short petals (3.5-4 x 0.7-1 cm) that are lanceolate and glabrous, and M. anomalum has short petals (3.6-6 x 0.8-1.5 cm) that are ovate-oblong and glabrous. The inner petals of M. vietnamensis (3.8-10.8 cm) are slightly longer than the outer petals (3.7-9.2 cm), whereas they are slightly shorter (ca. 3.5 cm and ca. 4 cm long in M. borneensis, and 3.5-5 cm and 4.5-6 cm long in M. anomalum, respectively). The fruiting pedicels of M. vietnamensis are longer (1.7-2.2 cm long) than those of M. borneensis (0.8-1 cm) or M. anomalum (ca. 1.5 cm).

In the present study, the number species of Monoon in Vietnam is raised to at least eight, viz. M. daclacense, M. harmandii, M.jucundum, M. laui, M. obtusum, M. simiarum, M. thorelii and M. vietnamensis. Flowers arise directly from tubercles, which were observed either from the main trunk or from the branches, are a common feature in Monoon and Annonaceae. The formation of flowers on the main trunk (cauliflory) is observed in several species in Borneo and Malaysia (such as M. bathrantherurn, M. con- gestatum and M. hypogaeum) (Turner 2013). However, tills is the first report of cauliflory among the Vietnamese species in the genus. The main distinguishing characters among the eight species in Vietnam are presented in a key to species below {see Appendix for a more detailed comparison).

Key to species of Monoon in Vietnam
1. Flowers arising from tubercles on trunk .....................................................................................M. vietnamensis
1. Flowers arising from old branches.............................. 2
2. Flowers solitary or cymes ........................................... 3
2. Flowers always cymes ................................................ 4
3. Flowers solitary or in cymes in axils of leaves (or of fallen leaves); trees 6-10 m tall; leaf laminas elliptic or broadly ovate; flowering peduncles ca. 1 cm long, with
3-5 bracts at base; petals narrowly ovate, glabrous........................................................................M. harmandii
3. Flower in cymes from old branches; shrubs 3-5 m
tall; leaf laminas oblong-elliptic; flowering peduncles 1.5-2 cm long, with a single bract at middle; petals oblong-lanceolate, sparsely tomentose at base of abaxial surfaces .................................................M. daclacensis
4. Petals hairy on both surfaces ...................................... 5
4. Petals glabrous or basally hairy abaxially................... 6
5. Flowers in single cymes from old branches; sepals tomentose on both surfaces; petals oblong-ovate, 1.7-3 x 0.4-0.6 cm; ovary hairy at apex; young twigs hairy; leaf laminas obovate or elliptic; veins 16-18 pairs per leaf .. ..................................................................M.jucundum
5. Flowers in distichous cymes from old branches or fascicles on tip of branches; sepals puberulous on abaxial surface only; petals narrowly ovate, ca. 1 x 0.3 cm; ovaiy sparsely pubescent; young twigs glabrous; leaf laminas oblong; veins 9-12 pairs per leaf......................................................................................................... M. thorelii
6. Petals oblong, abaxial surface glabrescent; petioles glabrous ............................................................................ 7
6. Petals ovate or narrowly ovate, abaxial surface puberulous; petioles hairy .............................................M. laui
7. Leaf laminae oblong or obovate; vems 12-14 pairs per leaf; petals 3.5-5.5 x 0.4-0.5 cm; ovary hairy; style glabrous; ripe fruits pale yellow ..................... M. obtusum
7. Leaf laminae ovate or oblong-elliptic; veins 15-17 pairs per leaf; petals 2-3 x 0.3-0.4 cm; ovaiy hairy at apex; style hairy; ripe fruits orange, grey to bluish-black ..........................................................................M. simiarum

Acknowledgements
This study was funded by the ITB Key Laboratory of Plant Cell Biotechnology (no. 09/TH-SHNĐ/17/03/2016) and the International collaboration project between Vietnam Academy of Science and Technology, Vietnam and Centre national de la recherche scientifique, France 183 (VAST. HTQT.PHAP.02/N16-17). I am also indebted to Assist. Prof. Dr. Hoàng Nghĩa Son, the director of Institute of Tropical Biology (ITB), for Ills continuing support to my plant research, to Mr. Tr an Văn Hùng for his assistance in the field. I am also thankful to Ian Mark Turner (K), Prof. Richard M.K. Saunders (The University of Hong Kong) for their constructive comments on this manuscript.

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Ann. Bot. Fennici 54: 153-158

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