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THAI FOR. BULL. (BOT.) 36: 18–45. 2008.

A checklist of the genus Tarenna Gaertn. (Rubiaceae) in Thailand

WIROT KESONBUA* & PRANOM CHANTARANOTHAI*

ABSTRACT. A checklist of the genus Tarenna in Thailand is presented. Twenty-four species and one variety are recorded. T. cinnamomea Craib, T. elliptica Craib, T. pubescens Craib and T. viridis Craib are reduced to synonymy of T. pulchra (Ridl.) Ridl., T. collinsae Craib, T. cinerea Craib and T. puberula Craib, respectively. A key to the species is provided, together with ecological data and information on the geographical distribution. Some species are illustrated.

INTRODUCTION

The generic name Tarenna was established in 1788 when J. Gaertner described the genus in his De Fructibus et Seminibus Plantarum. The genus name is based on the vernacular name of T. zeylanica Gaertn., which was known to the natives of Ceylon as Tarennae (Merrill, 1920). The genus contains ca 180 species, and is distributed in the tropical parts of Asia and Africa (De Block & Robbrecht, 1998) with species occurring in primary evergreen forests and scrub in the lowlands as well as at higher altitude.

The delimitation of the infrageneric elements of the genus Tarenna is largely based on placentation and seed type which are both very variable in morphology and anatomy (Bridson 1979; De Block et al. 2001). For example, in terms of placentation, the number of ovules per locule varies from one to numerous; they may be (partly) immersed in the placenta or pendulous from it; the placenta itself may be attached at the upper half, the middle or at the lower half of the septum. Seeds are very diverse too, e.g. the number and shape of the seeds range from a single spherical seed to numerous small angular seeds; the endosperm is ruminate or entire; their exotestal cells are parenchymatous to thickened at the outer tangential and radial walls (De Block 1997; De Block & Robbrecht 1998). The systematic affinities of the genus have been discussed by Verdcourt (1958), Bremekamp

  • (1966)

    , and recently byAndreasen & Bremer (1996), De Block et al. (2001) and Degreef et al.

  • (2001)

    . The genus is placed in the tribe Pavetteae, subfamily Ixoroideae, and Hooker (1880)

separated the genus (as “Webera”) into two sections for the Asiatic species, based mainly on the number of ovules per locule. The first section, Euwebera, had two ovules or more in each locule. The second one, Pseudixora, had one ovule per locule.

Like many Rubiaceae genera, the genus Tarenna is very poorly known in Thailand. Craib (1915) described three new species, T. collinsae Craib, T. pauciflora Craib and T. vanprukii Craib. Later, 22 species and 11 varieties were recorded in the Florae Siamensis

  • *

    Applied Taxonomic Research Center, Department of Biology, Faculty of Science, Khon Kaen

University, Khon Kaen 40002, Thailand.

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