Syzygium Gaertn. is the largest genus in Myrtaceae with about 1,200 species of mostly medium to large trees occurring in the tropics and subtropics from India to the Pacific Islands, and found in a diverse range of habitats from sea shore to montane forest. Perhaps the most frequently encountered species is clove, the unopened flower bud of S. aromaticum. Other species such as S. aqueum (Rose apple) and S. cumini (Java plum) are planted for their edible fruits, while some such as S. jambos have become invasive in island ecosystems. As one of the largest families of fleshy fruit bearing trees in the tropics, Syzygium is an important food source for wildlife (Parnell and Soh 2018, Soh 2017; Soh and Parnell 2015). In this research, Syzygium is taxonomically revised for Indochina, i.e. Cambodia, Laos and Vietnam. The species key, descriptions, typification, ecology, conservation status, phenology, vernacular names, usages, distribution maps and list of specimens examined were given. Over 4000 specimens from Indochina and other regions were examined and 63 names were lectotypified (Soh and Parnell 2012, 2015). This work is currently expanded for the revision of the family Myrtaceae for the Flora of Cambodia, Laos and Vietnam.
Figure 1. Syzygium bokorense W.K.Soh & J.Parn., one of the three new species described in this study (Soh and Parnell 2012).
A comparative study of the leaf anatomy of Syzygium was undertaken together with DNA analysis, to assess the taxonomic value of anatomical character at circumscribing subgeneric groups. We found that a combinations of non-unique leaf anatomical characters, including stomatal types, crystal types and frequency, and midrib vascular system were diagnostic for subgeneric groups (Fig. 2). Furthermore, the inclusion of anatomical characters in phylogenetic analysis did improve the phylogeny of Syzygium (Soh and Parnell 2011).
Figure 2. Leaf micromorphological structures of Syzygium showing crystals (top left), stomata (top right), trichome (bottom left) and vascular system (bottom right).
Parnell J. & Soh W.K. 2018. Nomenclature and typification of various Myrtaceae occurring in Southeast Asia. Edinburgh Journal of Botany 75: 205-214. DOI: 10.1017/S0960428618000057
Soh W.K. 2017. Taxonomy of Syzygium. In: The Genus Syzygium: Syzygium cumini and Other Underutilized Species (ed. Nair, K.N.). CRC Press, New York (ISBN 9781482249729)
Soh W.K. & Parnell. J. 2015. A revision of Syzygium (Myrtaceae) in Cambodia, Laos and Vietnam. Adansonia 37: 179-275
Soh W.K. & Parnell J. 2012. Three new species of Syzygium Gaertner (Myrtaceae) from Indochina. Kew Bulletin 66: 1-8. DOI: 10.1007/s12225-011-9305-9
Soh, W.K. & Parnell J. 2011. Comparative leaf anatomy and phylogeny of Syzygium Gaertn. Plant Systematics and Evolution, 297: 1-32. DOI: 10.1007/s00606-011-0495-2