Abstract
Ridsdalea alba, a new species of Gardenieae from southern Thailand, is described and illustrated. It differs from R. sootepensis in having narrowly elliptic-oblong to obovate leaf blades that are glossy dark green above, thickly leathery in texture, with rounded to acute leaf apices, and revolute leaf margins. Moreover, the corolla tube is without purple speckles inside.
References
<p class="Reference">Angiosperm Phylogeny Group [APG IV] (2016) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. <em>Botanical Journal of the Linnean Society </em>181: 1–20.</p><p class="Reference"> https://doi.org/10.1111/boj.12385</p><p class="Reference">Bremekamp, C.E.B. (1957) Some new Acanthaceae and Rubiaceae from Laos (Indo-China). <em>Proceedings van de Koninklijke Nederlandse Akademie van Wetenschappen, Series C: Biological and Medical Sciences </em>60: 1–8.</p><p class="Reference">IPNI (2016) <em>The International Plant Name Index</em>. Royal Botanic Gardens, Kew. Available from: http://www.ipni.org (accessed 16 October 2016)</p><p class="Reference">IUCN (2012) <em>The IUCN Red list of Threatened Species</em>, Version 3.1. Available from: http://www.iucnredlist.org (accessed 19 May 2016)</p><p class="Reference">Khammongkol, K., Chamchumroon, V., Tetsana, N., Poopath, M., Wai, J.S. & Sungkaew, S. (2016) <em>Rothmannia macrophylla</em> (Rubiaceae), a new record for Thailand. <em>Thai Forest Bulletin</em> (Botany) 44 (1): 32–34.</p><p class="Reference"> https://doi.org/10.20531/tfb.2016.44.1.07</p><p class="Reference">Mouly, A., Kainulainen, K., Persson, C., Davis, A.P., Wong, K.M., Razafimandimbison, S.G. & Bremer, B. (2014) Phylogenetic structure and clade circumscriptions in the Gardenieae complex (Rubiaceae). <em>Taxon</em> 63 (4): 801–818.</p><p class="Reference"> https://doi.org/10.12705/634.4</p><p class="Reference">Thunberg, C.P. (1776) <em>Kongl. Vetenskaps Academiens Handlingar.</em> Stockholm. 67–68 + Tab. II.</p><p class="Reference">Wong, K.M. & Pereira, J.T. (2016) A taxonomic treatment of the Asiatic allies of <em>Rothmannia </em>(Rubiaceae: Gardenieae), including the new genera <em>Ridsdalea</em> and <em>Singaporandia. Sandakania</em> 21: 21–64.</p><p>World Checklist of Rubiaceae (2016) <em>World Checklist of Selected Plant Families.</em> Available from: http://apps.kew.org (accessed 15 March 2016)</p>