Hoya isabelchanae Rodda & Simonsson, a new, showy species of Hoya R.Br. (Apocynaceae, Asclepiadoideae) with pomegranate red flowers from Sulawesi, Indonesia

Abstract A new species of Hoya R.Br. from Sulawesi (Indonesia), Hoya isabelchanae Rodda & Simonsson, is described and illustrated. It is one of the largest flowered species in Hoya section Acanthostemma (Blume) Kloppenb. Its flowers are of comparable size to those of Hoya benchaii Gavrus et al., Hoya kloppenburgii T.Green, Hoya rundumensis (T.Green) Rodda & Simonsson and Hoya sigillatis T.Green ssp. sigillatis, all from Borneo. Among Sulawesi species it is compared with the vegetatively similar Hoya brevialata Kleijn & van Donkelaar and Hoya pallilimba Kleijn & van Donkelaar.


Introduction
Th e Hoya R.Br. diversity of Sulawesi (Indonesia) was investigated rather comprehensively by Kleijn and van Donkelaar (2001) who supported their herbarium studies with extensive fi eld investigations throughout Sulawesi and not only collected herbarium specimens but also made extensive collections of sterile plants for growing ex situ.
Etymology. Hoya isabelchanae is named after Isabel Claire Chan Yuen Ching, late daughter of Elisabeth Chan, Singaporean patron of botanical research and a gardener with an interest in Hoya.
Distribution and ecology. Hoya isabelchanae is only known from the base of Gunung Boliohutu, Sulawesi, where it was collected as a sterile cutting in 2002 and brought into cultivation at the Royal Botanic Garden Edinburgh where it regularly blooms in a heated greenhouse from May to October. Th e species was collected in primary forest and it was growing in shaded but exposed area on a decaying tree 12 m tall. A further collection is widely available in cultivation under Gerard Paul Shirley number GPS10161 and 7-35 http://www.paulshirleysucculents.nl/shop_hoyas.htm [accessed on 24 June 2016]. Th is accession is apparently also from Sulawesi but no further collection information is available.
Conservation status. Th e only localised specimen of Hoya isabelchanae is the type collection. No information is available on the extent of the wild population in Sulawesi and the threats to its habitat therefore its conservation status is Data Defi cient (DD) (IUCN 2014). Hoya isabelchanae is at present in cultivation at the Royal Botanic Gardens Edinburgh (type collection, acc. no. 20021229) and at the Singapore Botanic Gardens (unlocalised collection, vouchered as M. Rodda MR573).
Among Sulawesi Acanthostemma members, H. isabelchanae is vegetatively similar to H. brevialata and H. pallilimba, that make large clumps of prostrate and pendant stems and have convex round to elliptic laminas. Th ey also have similar positively geotropic convex infl orescences. However H. isabelchanae can be separated from H. brevialata and H. pallilimba because it has much larger fl owers, both H. brevialata and H. pallilimba have fl owers c. 5 mm across while H. isabelchanae has fl owers 8-10 mm in diameter. Th e corona of H. isabelchanae has almost fl at lobes while the coronas of H. brevialata and H. pallilimba have the inner lobe held much higher than the outer lobe process. Further, the corolla of H. brevialata and H. pallilimba is fi nely pubescent while the corolla of H. isabelchanae is setose.
L, M, MO, P, SAN, SAR, SNP, SING, TO, UC, US, W, WRSL and WU herbaria for allowing access and/or for providing high quality images of herbarium specimens and Ulrich Meve for his contributions to the text. Elisabeth Chan is thanked for her continuous support of the research of both authors and for the English revision. Lastly we are grateful to Papaschon Chamwong for donating a live specimen of Hoya isabelchanae to the Singapore Botanic Gardens.