Hoyas | A deep dive

Going.Local
Published on February 25th 2021
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Hoya bella
Hoyas have captured the hearts of many hobbyists for their fragrant blooms and rambling nature. Climbing their way through Southeast Asia and Australia, you can find them from coastal beaches to high mountain ranges. Adapting to such vastly different climates is what makes each species unique.
It is also what makes them difficult to grow since no two are alike. In order to help you learn more about these fascinating plants, we are taking a deep dive into Hoya names, growing conditions and helpful guides for the avid collector.
Hoya carnosa

Hoya names and nomenclature

This is probably the most confusing part for beginners to grasp. Identification of a Hoya is a slow process and due to the large number of specimens collected and cultivated (along with the five odd years it takes to flower) a plant may take up to 10 years to be officially registered.
In the meantime, a plant is given an arbitrary name until it can be classified. Here is a quick explanation of the differences with a few examples.
Example: Hoya australis ssp. oramicola
- Hoya: Genus
- australis: species (the word itself referring to Australia)
- ssp: Abbreviation referring to subspecies
- oramicola: subspecies name
Example: Hoya sp. aff. picta
- Hoya: Genus
- sp: Abbreviation for 'species', yet to be classified
- aff: Abbreviation for affinity referring to the fact that the plant looks like (shares some characteristics with) Hoya picta, but is not identical.
Example: Hoya cv ‘Sunrise’
  • Hoya: Genus
  • cv: Abbreviation for cultivar or cultivated variety
  • Sunrise: The name the hybridiser gave the plant
It can also be called Hoya lacunosa ssp. pallidiflora × Hoya obscura, which show the two parents used to make the hybrid.
Example: Hoya sp. Sarawak GPS 10073
  • Hoya: Genus
  • sp.: Abbreviation for species and yet to be classified
  • Sarawak: Refers to a location in Borneo
  • GPS 10073 Is the accession assigned by the collector
    IPPS = Institute for Protection and Propagation of Succulent Plants
HSI= Hoya Society International
DMC= David M. Cimming
GPS= Gerard Paul Shirley
PNG= Papua New Guinea
IML = Iris Marie Liddle (David Liddle named it after his wife)
*The list is endless. For a longer more comprehensive list see here.
Hoya obovata
Sunstress, if done gradually, can give the plants an orange hue.

Growth conditions

As I mentioned in the introduction, Hoya can inhabit different climates. To narrow down the growing conditions, David Liddle used a temperature guide to indicate what a Hoya species prefers in terms of growing conditions. This remains one of the easiest guides to follow:
Categories:
  • Cool: Plants that cannot tolerate temperatures above 25C, but may be able to go as low as 10C for prolonged periods.
  • Temperate: Plants that can tolerate down to 10C, but can periodically go up to 35C.
  • Warm: Tropical species that cannot tolerate temperatures below 15C and grow happily at temperatures in the high 20 up to 35C.
The guide does not give an indication of humidity or watering requirements, which is something that can be deduced from the location it was originally collected. What is important though is to note that a great deal of Hoyas prefer temperatures that may be uncomfortable to live in (create indoors). Such species may require a greenhouse or if you are lucky enough to be situated in South Africa’s green belt, you can grow them outside.
Hoya linearis
Cool Growers *Ideal for indoor houseplants
Intermediate Growers
  • Hoya callistophyla (Sabah, Borneo)
  • Hoya caudata (Sumatra, Malaysia)
  • Hoya curtisii (Philippines, Thailand)
  • Hoya deykei (Sumatra)
  • Hoya elliptica (Malaysia)
  • Hoya finlaysonii (Malaysia, Phuket)
Warm Growers
  • Hoya latifolia
  • Hoya megalaster
  • Hoya subcalva (Solomon Islands)
  • Hoya kloppenburgia (Sabah, Borneo)
  • Hoya mindorensis (Sabah)
  • Hoya lambii (Sabah)
Hoya pest mealybug
Mealy bugs will hide in crevices and on new leaves. Be careful when removing them.

Pests and Diseases

Hoyas are resilient by nature, but that does not mean you will not stumble across the inevitable pests that plague milkweeds.
The most common problems are:
Each pest or disease profile above will give you an indication of how to treat it. The best advice one can give is to watch out for mealybugs in spring through summer, and root rot in winter.
Hoya flower drop hoya linearis
Too much water or fertiliser can result in bud drop.

A helping hand

When you find yourself bitten by the Hoya bug, it might prove helpful to get an insight into their habitats. The first step is to find out where they were collected. Several guide books describe both origin and plant characteristics.
Some suggestions:
  • A Guide to Hoyas of Borneo, Flora of Malaysia
  • The Hoya Handbook: A Guide for the Grower & Collector
  • Illustrated Handbook of Succulent Plants: Asclepiadaceae (It covers origin and description of Hoya, Dischidia, Cynanchum and all the other genera that fall within this group.)
For a quick look at the Borneo climate see:
Beginners will find a lot of help from existing hobbyists such as Dugg chamberlain from Vermont Hoyas and David Liddle’s original catalogues. These are not exhaustive but will show you why some species grow so extremely slowly while others triple in size.

If you found this helpful, remember to let us know in the comments below.

Hoya pauciflora
Bibliography:
Rodda, Michele. (2017). Index of names and types of Hoya (Apocynaceae: Asclepiadoideae) of Borneo. Gardens' Bulletin Singapore. 69. 33-65. 10.26492/gbs69(1).2017-02.
Rahayu, Sri & Rodda, Michele. (2019). Hoya of Sumatra, an updated checklist, three new species, and a new subspecies. European Journal of Taxonomy. 2019. 10.5852/ejt.2019.508.
Albers, F., & Meve, U. (2002). Illustrated Handbook of Succulent Plants: Asclepiadaceae: Asclepiadaceae (Vol. 4). Springer Science & Business Media.
Flora of Malaysia i-Newsletter Part 3. Forest Research Institute Malaysia (FRIM). (2013, 10). Retrieved February 12, 2021, from https://www.mybis.gov.my/art/1985
Henderson, C. P., & Hancock, I. R. (1988). A guide to the useful plants of Solomon Islands. Research Department, Ministry of Agriculture and Lands.
Lamb, A., Rodda, M., Gokulsing, L., Bosuang, S., & Rahayu, S. (2016). A guide to Hoyas of Borneo. Natural History Publications (Borneo).
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