Mallotus Lour. is a large genus of c. 150 species in Euphorbiaceae, subfamily Acalyphoideae, subtribe Rottlerinae (Sierra et al., 2007). Although two species in the genus occur in Africa and Madagascar, most are from tropical Asia with over 34 species known from Vietnam (Thin, 1999, 2007).

During an expedition to Phong Nha - Ke Bang National Park in the summer of 2006, an undetermined collection of Mallotus with shrubby habit, many submarginal extrafloral nectaries and cauliflorous inflorescences and fruits in the lower stem was collected. Based on comparisons with herbarium specimens at HNU and HN, and a study of the pertinent literature (Airy Shaw, 1972, 1975; Pax & Hoffmann, 1914; Ho, 1999; Thin, 1999, 2007; van Welzen et al., 2007), we determined that this collection did not correspond to any previously known Mallotus species. This new species is thus described below.

This new species differs from other species in Mallotus sect. Axenfeldia by its shrubby habit, presence of submarginal extrafloral nectaries along the leaf margin, and relatively few-flowered, cauliflorous inflorescences. — TYPE: Vietnam, Quang Binh Province, Phong Nha - Ke Bang National Park, Doc Tau area, 17°32'24''N, 106°16'59''E, 83 m, 1 July 2006, Nguyen Nghia Thin 20060701-09 (holotype HNU; isotype HN).

Fig. 2. Mallotus phongnhaensis Thin & Kim Thanh.
A. Details of leaves with submarginal extra-floral nectaries. B. Top view of fruit. C. Staminate flower. (Drawn by Nguyen Quang Hung)

Shrub up to 1 m high, dioecious. Indumentum scattered, composed of stellate hairs. Branches with scattered hairs, cylindrical. Stipules deciduous, triangular, c. 1.2 mm, flower per bract; bracts triangular, 2.2-2.5 x 1.2-1.6 mm. Staminate flower with 3 sepals that are elliptic to obovate, 3.2-3.7 x 1-1.3 mm; petals and disc absent; stamens 15-20, filaments 4-5 mm long; pistillode present. Pistillate inflorescences 2.5-3 cm long with 2-4 flowers, glabrous. Leaves opposite, equal in size; petiole 1.5-4 cm long, glabrous; blade elliptic, 11.5-21.5 x 5.5-11 cm, papery; base cuneate; apex acuminate, 1-1.5 cm long; margin entire or subentire; adaxial surface glabrous, extrafloral nectaries submarginal throughout blade, 6-12 per side, 0.3-1 cm from margin, elliptic to orbicular, 0.3-0.5 x 0.2-0.3 mm, conspicuous; abaxial surface glabrescent, with scattered glandular scales, mainly on basal or marginal nerves; venation pinnate, nerves 7-10 per side, arching and ending near margin, veins conspicuous. Staminate and pistillate inflorescences cauliflorous on lower stem, short and thick. Staminate inflorescences 2-3 cm long, with 10-15 flowers, one one flower per bract; bracts triangular, c. 1.5 mm long. Pistillate flower with 3 sepals; petals and disc lacking; ovary 3-locular, covered with stellate hairs and dense spines, spines 0.5-1 mm long; styles 0.2-0.3 mm long, stigmas c. 1.5 mm long, plumose. Fruit a loculicidal-septicidal capsule, c. 1.2 x 0.9 cm, on a long (up to 2 cm long) pedicel, spines sparse, blunt, c. 0.5-1 mm long; style persistent. Seed unknown.

Distribution and ecology. This species is only known from one population near a small stream within a humid forest not far from the road in Doc Tau area, Phong Nha - Ke Bang National Park, Quang Binh Province, Vietnam.

Flowering and fruiting. Mallotus phongnhaensis was observed in flower and fruit from May to July.

Etymology. The new species is named after its type locality.

Provisional IUCN conservation assessment. The type locality, the only known site, occurs within Phong Nha - Ke Bang National Park and is, therefore, under protection. However, the population size of this new species is fewer than 100 mature individuals. We, therefore, assess it as Endangered EN D under the IUCN Red List categories and criteria (IUCN, 2001) because it has fewer than 250 mature individuals.

Notes. The most comprehensive revision of Mallotus in Vietnam was done by Thin (1999, 2007), who recognised six sections: Axenfeldia (Baill.) Pax & Hoffm., Hancea (Seem.) Pax & Hoffm., Rottleropsis Mull.Arg., Philippinense Pax & Hoffm. (formerly section Rottlera Airy Shaw), Stylanthus (Reichb.f. & Zoll.) Pax & Hoffm. and Mallotus Mull.Arg. With its opposite leaves and pinnate venation, Mallotus phongnhaensis clearly falls within section Axenfeldia, which currently includes eight known species in Vietnam. Our new species is different from others in this section by the occurrence of 6-12 extrafloral nectaries just behind the leaf margin and the cauliflorous flowering habit.

Airy Shaw, H.K. (1972). The Euphorbiaceae of Siam. Kew Bull. 26: 292-308.

Airy Shaw, H.K. (1975). Notes on Malesian and other Asiatic Euphorbiaceae. CXCIX. New or noteworthy species of Mallotus Lour. Kew Bull. 29: 401-407.

Ho, P.H. (1999). An Illustrated Flora of Vietnam. 2: 248-256. Hanoi, Vietnam: Youth Publ. House.

IUCN (2001). IUCN Red List Categories and Criteria, Version 3.1. Gland, Switzerland, and Cambridge, United Kingdom: IUCN Species Survival Commission. IUCN.

Pax, F. & Hoffmann, K. (1914). Euphorbiaceae-Acalypheae-Mercurialinae. In: Engler, A. (ed) Das Pflanzenreich, IV, 147, vii: 145-208. Leipzig, Berlin: Wilhelm Engelmann.

Sierra, S.E.C., Aparacio, M., Gebraad, M.J.H., Kulju, K.K.M. & van Welzen, P.C. (2007). The morphological range in Mallotus (Euphorbiaceae) and a taxonomic revision of its section Rottlerpsis (including Axenfeldia) in Malesia, Thailand and Africa. Blumea 52: 21-113.

Thin, N.N. (1999). Key to taxa and classification of Euphorbiaceae of Vietnam. Hanoi, Vietnam: Agr. Publ. House.
Thin, N.N. (2007). Taxonomy of Euphorbiaceae in Vietnam. Hanoi, Vietnam: VNU Publ. House.

Welzen, P.C. van, Sierra, S.E.C., Slik, J.W.F. & Bollendorff, S. (2007). Mallotus. In: Welzen, P.C. van & K. Chayamarit, K. (eds) Flora ofThailand 8, 2: 384-437. Bangkok, Thailand: The Forest Herbarium, National Park, Wildlife & Plant Conservation Department.