Amorphophallus kienluongensis ( Araceae ) , a new species from the Mekong Delta , Southern Vietnam

Amorphophallus kienluongensis is described as a new species from southern Vietnam. It is morphologically close to A. brevispathus Gagnep. (Thailand) and A. prolificus Hett. & A.Galloway (Thailand). However, it differs from both these species by a stigma with a central depression and an obconic male portion. So far A. kienluongensis is known only from the Kien Luong district of the Kien Giang province, southern Vietnam. The plant grows on limestone hills where its habitat is under threat owing to quarrying for cement manufacture. Therefore this species could be ranked as CR (‘critically endangered’) in the IUCN ranking.


INTRODUCTION
The genus Amorphophallus includes c. 200 species (Sedayu et al. 2010, Hetterscheid et al. 2012) distributed throughout tropical Africa and Asia with one species in N Australia (Sedayu et al. 2010).Most species are adapted to life in tropical humid forests, seasonal forests, and grass savannahs, often on slopes, in forest margins, secondary forest.Many species are adapted to humus pockets on limestone.
During a field trip at Chua Hang Hill in 2009, the first author collected the new species in leaf.Later Dr Luu Hong Truong and his colleague Nguyen Quoc Dat found the species flowering at Hang Tien and Khoe La Hills in the Kien Luong district of the Kien Giang province.Herbarium specimens were sent to the first author for identification as well as several pictures to the third author.It was recognized as an undescribed species and the proposed name is A. kienluongensis.It is morphologically close to A. brevispathus (Gagnepain 1941) from Thailand in having a very short spathe relative to the spadix and the male flowers in clusters of more than 6.However, A. brevispathus is distinguished e.g. by a very irregularly shaped tuber with numerous thick, long rhizomatous offsets and stigma diameter smaller than the ovary.In this paper, the new species is described, with its distribution, ecology, biology, and conservation status.

DESCRIPTION
Amorphophallus kienluongensis V.D. Nguyen, Luu & Hett., sp.nov.-Fig. 1 Diagnosis: Amorphophallus kienluongensis resembles A. brevispathus in having a spathe shorter than the spadix and the male flowers clustered in groups of 6 or more.It differs from A. brevispathus in the stigma diameter exceeding that of the ovary and in having a tuber without long rhizomatous offsets.
Etymology.The species epithet kienluongensis is derived from the name of the Kien Luong district of the Kien Giang province, Vietnam.
Ecology -Coastal forests on karst limestone, 5 -50 m altitude.Flowering in June and fruiting in September.
Conservation status -Amorphophallus kienluongensis is known to occur only on several small adjacent isolated limestone hills including Khoe La, Hang Tien, Chua Hang, and Ba Tai in the Kien Luong district.Khoe La is quarried for cement manufacture, and it is foreseen it will be destroyed within the next years.The area in which the species grows is less than 3 km 2 and combined with threats from quarrying the species is recommended to be ranked as globally Critically Endangered (CR) according to the IUCN Red List criteria (v.2.3) (http:// www.iucnredlist.org).Notes -The combination of characters in A. kienluongensis of male flowers in large groups, a rupturing connective, and berries ripening blue suggests the species to be a member of a subclade of five other species with this same unique character combination: A. atrorubens Hett.& Sizemore (Hetterscheid & Van der Ham 2001, Thailand), A. brevispathus (Thailand), A. gallowayi Hett.(Hetterscheid 2006, Thailand), A. interruptus Engl.& Gehrm.(Engler 1911, N Vietnam), and A. prolificus (Hetterscheid 2006, Thailand).Sedayu et al. (2010: 482, f. 3) failed to resolve these species as a monophyletic group although only two species (A.brevispathus and A. interruptus) were included.As yet unpublished molecular phylogenetic information based on 130 species, resolved the above listed species as a monophyletic group with full statistical support (Baysian post.prob.= 1).

Fig. 1
Fig. 1 Amorphophallus kienluongensis V.D. Nguyen, Luu & Hett.a. Habitat and habit with mature leaves; b. habitat and habit with seedling and more mature leaves; c. inflorescence; d. spadix exposed; e. ovary and stamens; f. infructescence with mature fruits; g. fruit in longitudinal and cross section.-Scale bar = 1 cm.