For more than 20 years I studied the genus Hoya and there relatives Dischidia, Absolmsia and Micholitzia.
On our former nursery we collected more than 800 live specimen of these genera and about 500 other species of the family Asclepiadaceae such as Stapeliads and Ceropegias. I visited several times Indonesia to study these genera in the field and to collect specimen for the reference collection: IPPS. Our collection is now part of the collections at the Botanical Gardens at Leiden.
Hoya darwinii IPPS 2028 
Hoya dimorpha IPPS 259
Hoya species Brunei IPPS 3572Hoyacuttings of my former collection are available at:
Kakteen-Haage, Erfurt , Germany , www.kakteen-haage.de
Ted Green Plant Research , Hawaii , USA , www.rare-hoyas.com
Paul Shirley , Boskoop , Netherlands , www.paulshirleysucculents.nl
Hoya curtisii IPPS 1779
Hoya imbricata IPPS 1107RECENT PUBLICATIONS:
Towards a Monophyletic Hoya (Marsdenieae, Apocynaceae): Inferences from the Chloroplast trnL Region and the rbcL-atpB Spacer
Livia Wanntorp, Alexander Kocyan, Ruurd van Donkelaar, Susanne Renner
in Systematic Botany (2006), 31 (3):pp. 586-596(11)
www.sysbot.org
Abstract:
The delimitation of the genus Hoya, with at least 200 species distributed from India and China to Australia, from its closest relatives in the Marsdenieae has long been problematic, precluding an understanding of the evolution and biogeography of the genus. Traditional circumscriptions of genera in the Hoya alliance have relied on features of the flower, but these overlap extensively between clades and may be evolutionarily labile. We obtained chloroplast DNA sequences to infer the phylogenetic relationships among a sample of 35 taxa of Hoya and 11 other genera in the tribe Marsdenieae, namely Absolmsia, Cionura, Dischidia, Dregea, Gongronema, Gunnessia, Madangia, Marsdenia, Micholitzia, Rhyssolobium, and Telosma. Trees were rooted with representatives of Asclepiadeae, Ceropegieae, Fockeeae, Periplocoideae, and Secamonoideae. Hoya and Dischidia form a monophyletic group, but the phylogenetic signal in the chloroplast data analyzed here was insufficient to statistically support the mutual monophyly of the two genera. A monophyletic Hoya, however, must include the monotypic Absolmsia, Madangia, and Micholitzia, a result congruent with their flower morphology. The data also identified several wellsupported groups within Hoya. The morphologically unusual Gunnessia belongs firmly in the Marsdenieae, but it is not close to Hoya and Dischidia.
Keywords: CHLOROPLAST; FLOWERS; HOYA; MARSDENIEAE; PHYLOGENY; RBCL-ATPB SPACER; TRNL REGION
R. van Donkelaar en D. Kleijn, ‘Notes on the taxonomy and ecology of the genus Hoya (Asclepiadaceae )'. In : Central Sulawesi in Blumea 46. 2001. p. 457-483.
www.nationaalherbarium.nl/pubs/blumea/blumea463.htm#Hoya
Abstract:
The taxonomy and ecology of the genus Hoya R.Br. are unclear, especially in the core area of its distribution: Sumatra, Borneo, Sulawesi and Irian Jaya. This paper summarises the available information on the ecology of Hoya species, and describes eight species from central Sulawesi. An important ecological trait of many Hoya species is their association with ants. Four types of mutualistic relationships with ants occur in the genus: 1) species with specialised leaves to house ants; 2) a single species that provides housing for ants under imbricate leaves; 3) species growing on the carton of ant nests; and 4) species that root in ant inhabited cavities in tree trunks and branches. Four of the eight described species grew in association with ants (types 2–4).
Taxonomically, Hoya sussuela (Roxb.) Merr. is placed in synonymy with H. coronaria Blume, and H. maxima (H. Karst.) Warb. and H. pseudomaxima Koord. are reduced to H. imbricata Decne.
Three new species are described:
Hoya brevialata Kleijn & Van Donkelaar
Hoya myrmecopa Kleijn & Van Donkelaar
Hoya pallilimba Kleijn & Van Donkelaar
F. Albers, R. van Donkelaar en C. Hoffmann, ‘Hoya, Dischidia'. In: Albers und Meve, Sukkulentenlexikon, band 3, Asclepiadaceae.2002.
en in:
Albers und Meve , Illustrated Handbook of Succulent Plants : Asclepiadaceae. 2002.
