Hiepia corymbosa - New genus of Apocynaceae (Asclepiadoideae) from Vietnam

Introduction

The subfamily Asclepiadoideae (Apocynaceae) comprises 250 genera with over 2000 species widespread in tropical and subtropical regions with highest diversity in Africa and in the south of South America. Subfamily has also well representation in northern and southeastern Asia (Li et al., 1995). In Vietnam 48 genera with 122 species of this subfamily were listed until now (Tran The Bach, 2005). During our recent plant collecting fieldwork in central Vietnam, some unusual specimens of Asclepiadoideae were discovered. Detailed study of collected plant revealed obvious fact that it does not fit any presently known asclepioid genera having, nevertheless, obvious relation to Dischidia R. Br. and Hoya R. Br. well presented in the flora of Vietnam by 12 and 18 species respectively (Ho, 2003; Tran The Bach, 2005; Livshultz et al., 2005). Phylogenetically, the studied plant can be tentatively placed near mentioned genera on the base of comparative analysis of floral and vegetative morphology. However, some specific features give clear evidence that the novelty cannot belong to Dischidia, Hoya or any Turczaninowia 2011, 14(3) : 5–10.

Ecology

Hiepia corymbosa was observed as a humus or bark epiphyte on old mossy trees in primary broad-leaved evergreen forests along rocky river canyons composed with shale, sandstone and solid crystalline highly eroded limestone at elevation 300–500 m a.s.l. Samples of this plant were found in tree canopies along stream just along water line. Plants commonly settle down in forks of tree branches in more or less sunny places. The species of Aglaia, Antidesma, Artocarpus, Baccaurea, Canarium, Cryptocarya, Diospyros, Dipterocarpus, Dracontomelum, Dysoxylon, Elaeocarpus, Erismanthus, Ficus, Litsea, Manglietia, Michelia, Phoebe, Pometia, Sloanea, Sterculia, Stixis, Streblus, Sygyzium were observed as the most common trees in habitats of H. corymbosa as well as numerous palms, mainly Arenga caudatum, A. westerhoutii, Rhapis excelsa and species of Caryota and Pinanga. Some epiphytic ferns and orchids were observed as usual associates growing together with Hiepia corymbosa. Among such species most common are Bulbophyllum delitescens, B. longiflorum, Dendrobium terminale, D. truncatum, Kingidium deliciosum, Lemmaphyllum microphyllum, Phalaenopsis mannii, Pomatocalpa spicatum, Pyrrosia lanceolata and Thrixspermum centipeda. Among strict Vietnamese endemics found in habitats of newly discovered genus, Epipactis atromarginata, Eria thao, Ixodonerium annamense, Micropera poilanei and Pteroceras simondianum should be mentioned.

Distribution

Hiepia corymbosa commonly inhabits lowland rocky river valleys composed with shale, sandstone and limestone in Quang Binh (Minh Hoa district, Thuong Hoa municipality) and Quang Tri provinces (Da Krong district, Ta Rut municipality) of central Vietnam growing at elevation 300–500 m a.s.l. Most probably, discovered plant represents the pattern of strict endemism typical for highly endangered lowland aboriginal floras of Central Vietnam.
IUCN Red List category. Hiepia corymbosa is local Vietnamese endemic, which inhabits very limited areas in Quang Binh and Quang Tri provinces in central part of the country. Both known localities are currently endangered due to deforestation and human land exploitation. The species is certainly very rare and actually is known only from two populations with less than 10 observed mature individuals. Typical habitat areas extend along narrow river valleys with total land occupancy not more than 2–3 km². Vegetation supported known populations is highly depressed by anthropogenic activity and can be destroyed in the near future. According to accepted criteria (IUCN, 2010, version 8.1), H. corymbosa should be treated as critically endangered species and genus (CR) approaching full extinction in the nature.

Note

Morphologically, Hiepia corymbosa superficially resembles some representatives of Hoya and Dischidia. Common features of all three genera are epiphytic habit; succulent or leathery leaves; axillary, long living inflorescences with flowers approximated on very short apical rachis; valvate corolla lobes; pentafid corona, discoid gynostegium and stigma head; filaments connate with gynostegium; anther appendages covering stigma head; pollinaria with 2 pollinia, connected with translators to bifid corpusculum; pollinia granular united into massulae (poliades). At the same time, our plant strikingly differs from all known species of both mentioned genera mainly in revolute petals, flat corymbiform inflorescence, not stellar spreading corona and very long filiform translators. Principal diagnostic discriminative morphological characters of mentioned genera are presented in the following Table.

Table: Diagnostic discriminative morphological characters of Dischidia, Hoya and Hiepia

Fig. 1. Hiepia corymbosa
a – upper portion of flowering shoot, b – leaf, lower surface, c, d – flowers, view from behind and frontal view, e – open flower, side view, f – sagittal section of open flower, side view, g – flattened calyx, view from below, h – flattened corolla, view from below, i, j – floral bracts, k – pollinarium (all drown by authors from type specimen – CPC 3066).

Fig. 2. Hiepia corymbosa. Digital epitype
(d-EXSICCATES OF VIETNAMESE FLORA 0188/CPC 3066).

Acknowledgements

Authors cordially thanks organizers of our field works – Directorate of non-government organization “Center for Plant Conservation” (Vietnam Union of Science and Technology Associations) – Prof. Phan Ke Loc, Dr. Nguyen Tien Hiep and MSc. Nguyen Quang Hieu. Field work resulted in presented discovery was supported from U.S.A. National Geographic Society research program “Exploration of primary woods along constructed highway Hanoi – Ho Chi Minh for their sustainable conservation (in limits of Ha Tinh, Quang Binh, Quang Tri, Thua Thien - Hue, Quang Nam and Kon Tum provinces of central Vietnam” (Grant # 8800-10). We are grateful to Prof. Li and Dr. M. Rodda for their valuable comments of our work on Hoya diversity in Vietnam. We also cordially thank Dr. A. Sennikov for his kindest translation of abbreviated diagnosis into Latin.

Literature

1. Ho Pham Hoang. Asclepiadaceae // An Illustrated Flora of Vietnam. – Tre Publishing House, Ha Noi, 2003. – Vol. 2. – P. 724–755.
2. IUCN Standards and Petitions Subcommittee. Guidelines for Using the IUCN Red List Categories and Criteria. Version 8.1. Prepared by the Standards and Petitions Subcommittee in March 2010. http://intranet.iucn.org/webfiles/doc/SSC/RedList/RedListGuidelines.pdf.
3. Li P.T., Gilbert M.G., Stevens W.D. Hoya R. Brown // Wu Zheng-yi, P.H. Raven (eds). Flora of China. – Science Press, Beijing, Missouri Botanical Garden Press, St. Louis, U.S.A., 1995. – Vol. 16. – P. 228–236.
4. Livshultz T., Tran T.B., Bounphanmy S., Schott D. Dischidia (Apocynaceae, Asclepiadoideae) in Laos and Vietnam // Blumea, 2005. – Vol. 50, № 1. – P. 113–134.
5. Tran T.B. Asclepiadaceae // Checklist of Plant Species of Vietnam. – Vietnam National University, Hanoi, Vietnam Academy of Science and Technology and Missouri Botanical Garden. Agriculture Publishing House, Hanoi, 2005. – Vol. 3. – P. 58–75.

Key words: Hiepia corymbosa, new genus and species, Apocynaceae, flora of Vietnam, higher plant taxonomy, biological diversity.

phamvthe@gmail.com
Vietnamese Academy of Sciences and Technology, Institute of Ecology and Biological Resources, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Vietnam.
av_leonid@mail.ru; av_leonid@yahoo.com
Russian Academy of Sciences, Komarov Botanical Institute, Prof. Popov str., 2; 197376, St.-Petersburg, Russia.
(Turczaninowia 2011, 14(3) : 5–10)