| # & Species | Author | Region | Clade |
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In the horticultural trade, Hoya sp. (species unknown) designations are used for specimens that have not yet been formally described or identified to species. These are typically followed by a location and/or collector code:
The location indicates the geographic origin; the collector code references the individual plant clone or collection number. "sp. aff." (species affinis) means the plant closely resembles a known species but may be distinct. These designations are informal and not governed by the International Code of Nomenclature.
The Swedish Hoya Society (swedishhoyasociety.com) is the official International Cultivar Registration Authority (ICRA) for Hoya R.Br., appointed by the International Society for Horticultural Science (ISHS) in 2014. All official Hoya cultivar names must be registered with this body.
Official cultivar registrations are published in their quarterly journal Hoyatelegrafen and in Asklepios. The Society notes that approximately 910 published names exist across the genus (many are synonyms), with ~567 currently accepted per Plants of the World Online (POWO).
A cultivar (cultivated variety) is a plant selected for a distinctive trait and maintained through cultivation. Hoya cultivar names are written in single quotes after the species name: Hoya carnosa 'Tricolor'. Only the Swedish Hoya Society (as ICRA) can officially register new cultivar names for Hoya.
The clades shown in this tree are based primarily on molecular phylogenetic analyses from Wanntorp et al. (2014) and Rodda & Niissalo (2021; PMC8862764, Scientific Reports). The majority of the 567 accepted species remain unplaced in molecular studies due to the difficulty of collecting specimens from remote habitats. The tree topology shown is a consensus of currently published analyses and should be considered provisional.