Timonius, Candolle, 1830

Hoo, Pui Kiat, Sugumaran, Manickam & Wong, Khoon Meng, 2023, Two new species of Timonius (Rubiaceae: Guettardeae) from the Malay Peninsula, Phytotaxa 599 (3), pp. 171-182 : 174-175

An unusual Timonius with black bark from the Malay Peninsula

Timonius flavescens ( Jack 1823: 127) Baker (1877: 144) is commonly found in peat swamp forests mostly along coastal fringes including on coastal mountains where peaty substrates form. In the Malay Peninsula, it is one of the most widespread species, and although leaf shape and size can be variable, it is easily recognised in the field by its purplish midribs and secondary veins on the lower leaf surface, shagreened lower leaf lamina surface and 4-lobed fruits. While sorting through specimens in herbaria, a couple of collections (Md. Shah, Ahmad & Mahmud MS 3317 and Loh FRI 13500) seemed to be a distinctive species but yet possible to be included in the general circumscription of T. flavescens in Wong (1988). These two collections are here deemed distinct from T. flavescens based on ecology and general morphology including one unexpected character—bark colour.

All Malay Peninsula Timonius hitherto known share a common bark colour which ranges from grey to brown ( Fig. 3A ) and so this character was not thought of as being important in species delimitation. However, the new species was noted as having black bark, a character that thus stands out among the species in the Malay Peninsula. We were able to ascertain its bark colour from field observations ( Fig. 3B ).

The new species, here named Timonius denigricans P.K.Hoo due to the blackening of the bark, appears to be endemic to the Malay Peninsula. Its bark colour, although highly unusual for Timonius in the Malay Peninsula, apparently does occur in the genus, albeit rarely, in other regions. One such species is an endemic of the Solomon Islands — T. melanophloeus Merrill & L.M.Perry (1945: 251) , in which even the bark of the branchlets is black (the bark of the branchlets in T. denigricans is grey). Some other species appear to be more varied in their bark colour, often ranging from grey or brown to black such as T. timon ( Sprengel 1813: 18) Merrill (1937: 131) and T. trichocladus Merrill & L.M.Perry (1994: 78) from the Papuasian region as well as T. abanii Junhao Chen (2014: 139) and T. ophioliticus Junhao Chen (2014: 146) from Borneo island. However, these species either belong to very different subgenera, or have been recently revised and display different characteristics ( Chen & Wong 2023). Besides going through taxonomic literature, the search for Timonius with black bark was done through IPNI, focusing on species epithets that contain Latin or Greek terms for ‘black’ which are ‘niger’ and ‘melano-’, respectively.

Figures

FIGURE 3.A.Pale brown barkof Timonius flavescens, as in many other Malay Peninsula Timonius species.B. Black bark ofT.denigricans. Photos A by R.C.J. Lim and B by P.K. Hoo.