An updated and revised description of Timonius grandifolius (Rubiaceae: Guettardeae) and a new character observation for the tribe Guettardeae. Contributions to the Flora of Mt Jaya, XIX

Abstract

Summary. Dehiscent fleshy fruits are reported for the first time in Rubiaceae tribe Guettardeae based on collec-tions of Timonius grandifolius Valeton from Papua, Indonesian New Guinea. The descriptions for Timonius subgenusPseudobobea (Valeton) S. P. Darwin and T. grandifolius are amended, a distribution map and photographs provided,and a preliminary IUCN conservation assessment given.Key Words. Conservation assessment, dehiscent fruits, Malesia, New Guinea, Pseudobobea, taxonomy. Introduction The genus Timonius Rumph. ex DC., in the tribeGuettardeae, is one of the ‘top 20’ largest genera inthe Rubiaceae (Davis et al. 2009). Its centre of diversityoccurs on the island of New Guinea — of the 183known and accepted species of Timonius, 88 occur inNew Guinea and 81 of these are endemic (Govaerts etal. 2013). The island is one of the most poorlycollected tropical areas in the world, and one of thelargest remaining wilderness areas on the planet(Mittermeier et al. 2003). Over several years the RoyalBotanic Gardens, Kew has undertaken a researchprogramme in the Mt Jaya region of the southerncoastofIndonesianNewGuinea, with severalthousand collections from habitats throughout theentire altitudinal range from sea level to alpine scree(seeJohns etal.2006).Thesecollectionshaveyieldedtwointeresting Timonius specimens with white fleshy fruits,whichdehiscewhenripetoexposeseedsembeddedinabright white pulp (Fig. 1). Originally considered torepresentanewspeciesofTimonius, carefulconsultationofspecimensattheKewherbarium,imagesofspecimensfrom other herbaria and available literature highlightedsignificant overlap in character measurements anddistribution with Timonius grandifolius Valeton.A variety of fruit types are found in the Rubiaceae,the most common being dry capsules or indehiscentfleshy drupes (e.g., see Puff et al. 2005 for acomprehensive survey of genera). Mitragyna Korth.,Uncaria Schreb. and Wendlandia Bartl. ex DC. areexamples of dry, capsular fruited Rubiaceae generaand fleshy, drupaceous genera include Ixora L.,Lasianthus Jack and Psychotria L. Fruits of mostGuettardeae genera are documented as being drupa-ceous, and according to Robbrecht (1988) MachaoniaHumb. & Bonpl. (distributed from Mexico to tropicalSouthAmerica)istheonlygenusinthetribeGuettardeae with dehiscent fruits. Taylor & Gereau(2010) noted that Allenanthus Standl. was also dehis-cent but Govaerts et al. (2013) consider Allenanthus tobe a synonym of Machaonia. The fruits of the Mt JayaTimonius specimens are fleshy and dehiscent, asopposed to dry and capsular in Machaonia, leading usto believe that this is a previously undocumentedcharacter combination for both the genus and thetribe. A similar character state is observed in someGardenia J. Ellis species (tribe Gardenieae) such as G.elata Ridl., G. kabaenensis Y. W. Low, G. longistipula Y. W.Low, G. subcarinata (Corner) Y. W. Low and G. tubiferaWall. (all from South-East Asia). In these species,however, the fleshy fruits dehisce irregularly when ripebut the seeds are embedded in a bright yellow toorange-redpulpratherthanthebrightwhitepulpintheMt Jaya Timonius collections (Low & Wong 2009;WongLLow2013).Species of Timonius are dioecious and have corollalobes which are valvate to sub-imbricate in bud, severalto many locules in the ovary developing into individualone-seeded pyrenes, and drupaceous fruits with per-sistent calyces (Darwin 1994, 2010). Timonius has beensplit into three subgenera — Timonius, Abbotia S. P.Darwin and Pseudobobea (Valeton) S. P. Darwin, withseveral additional species gathered together in an, asyet, unranked species group (Darwin 2010; see alsoDarwin 1993, 1994, 1997).Timonius grandifolius is a member of Timoniussubgenus Pseudobobea (Valeton) S. P. Darwin whichhas been recently revised throughout its range(Darwin 2010). Our observations, however, of fruitdehiscence and the remarkable white colour at