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Family Apocynaceae

Hoya
Hoya carnosa (L. f.) R.Br.
WAX PLANT

Scientific names Common names
Asclepias carnosa (L. f.) R. Br. Hoya (Engl.)
Cynanchum carnosum Decne. Honey plant (Engl.)
Hoya carnosa (L. f.) R.Br. Hindu rope (Engl.)
Hoya chinensis (Lour.) Krinkle curl (Engl.)
Hoya intermedia A.C. Sm. Porcelain flower (Engl.)
Scholia carnosa (L.f.) Schrank ex Steud. Was flower (Engl.)
Scholia chinensis (Lour.) J. Jacq. Wax plant (Engl.)
Stapella chinensis Lour. Wax vine (Engl.)
Hoya carnosa (L.f.) R.Br. is an accepted name. The Plant List

Other vernacular names
CZECH: Voskovka masita.
DUTCH: Grote wasbloem.
ESTONIAN: Harilik vahalill.
FINNISH: Isoposliinikukka.
FRENCH: Fleurs de cire, Fleurs de porcelaine.
GERMAN: Porzellanblume, Wachsblumen.
ITALIAN: Fiore di cera.
POLISH: Hoja rozowa.
PORTUGUESE: Flor de cera.
SPANISH: Flor de porcelana, Flor de nacar, Flor de cera, Planta de cera, Cerilla.
VIETNAMESE: Cam cu.


Botanical snippet
- Hoya carnosa has been in cultivation for more than 200 years, with many cultivars that vary in foliage form or flower color.
- The genus Hoya was named by Robert Brown, a Scottish botanist and palaeobotanist.
- A genus of about 200-300 species, Hoya was earlier placed in the milkweed (Asclepiadaceae) family. Current taxonomy place the genus under the dogbane (Apocynaceae) family. (12)
- In 2017, it was given the UK Royal Horticultural Society's Award of Garden Merit. (10)

Botany
Hoya is a semi-woody, succulent perennial climbing vine. Leaves are glossy, waxy, succulent and grayish green, elliptic to broad-oval, up to 20 centimeters long. Flowers are faintly fragrant, in umbels, 3 to 5 inches in diameter, pinkish-white with a red star-shaped crown. Pods are long and thin, opening to release seeds similar to dandelion.

Distribution
- Indigenous to Australia, China and the Philippines.
- Ornamental cultivation.
- Popular as a hanging pot plant.


Constituents
• Flowers yielded
volatile compounds, viz., methyl butanal, ethylbenzene, o-xylene, p-xylene, benzaldehyde, 6-methyl-5-heptan-2-one, benzyl alcohol, linalool, 2-nonen-1-ol, phenylethylalcohol and 2-(E)-noneal.
• Stem yielded oligosaccharides A, B, and C (1-3) established as 6-deoxy-3-O-methyl-β-allopyranosyl(1→4)-β-cymaropyranosyl (1→4)-β-cymaropyranosyl(1→4)-β-cymaronic acid δ-lactone (compound 1) and 6-deoxy-3-O-methyl-β-allopyranosyl(1→4)-β-oleandropyranosyl(1→4)-β-cymaropyranosyl(1→4)-β-cymaronic acid δ-lactone (compound 2). Compound 3 was the sodium salt of compound 2. (6)

Properties
• Fragrance of flowers increase at night.
(see study below: 13)
• Studies have suggested anti-aging, air-purifying, antibacterial properties.

Uses
Folkloric
• No reported folkloric medicinal use in the Philippines.
Others
• Perfume: Scented flowers reportedly used in making perfume.
• Air-purifying plant: See study below. (1)

Studies
Volatile Compounds: Study isolated volatile compounds from the flowers of Hoya carnosa: methyl butanal, ethylbenzene, o-xylene, p-xylene, benzaldehyde, 6-methyl-5-heptan-2-one, benzyl alcohol, linalool, 2-nonen-1-ol, phenylethylalcohol and 2-(E)-noneal. (2)
Air-Purifying Plant: In a University of Georgia study, Hoya carnaso was shown to be good at absorbing VOCs. VOCs are volatile organic compounds, contaminants emitted by various common household items. More than 300 have been identified – carpets, wood panels, paints, pets, formaldehyde, benzene and toluene from old books, newspapers, waxes and adhesives. (1)
ADPglucose Pyrophosphorylase: ADPglucose pyrophosphorylase from Hoya carnosa and Xerosicyos danguyi were partially purified for their regulatory and kinetic properties. The ADPglucose synthesized by the enzymes was found to be the most effective donor of the glucosyl portion to alpha-glucan primer in starch synthase reaction observed in CAM plants. (1)
Hemolytic Crises Caused by H. Carnosa in G6PD Deficiency: Study reports a hemolytic crises caused by contact with Hoya carnosa in a 45-year old woman with G6PD deficiency. (7)
Use for Anti-Aging Benefits / Patent: Patent application relates to the incorporation of Hoya carnosa extracts and their use to reduce fine lines and wrinkles, improve sagging skin, enhance lifting, and improve skin tone and to improve overall appearance by increasing epidermis thickness and stimulating collagen, and/or inducing lipogenesis. (9)
• Nectar Secretion: Study describes a continuous sampling of nectar secreted in single flowers of Hoya carnosa. Sampling at 3-hour intervals over several days revealed an oscillating secretion with maxima around midnight. Study suggests the rhythmicity of nectar secretion in H. carnosa is a manifestation of the biologic clock. (11)
• Circadian Rhythmicity of Flower Fragrance Emission: Flowers of Hoya carnosa exhibits nocturnal emission of fragrance according to an endogenous circadian rhythmicity, demonstrated by rhythmical emission for two to three cycles under conditions of permanent illumination. (14)
• Antibacterial / Leaves: Study evaluated the antibacterial activity of Hoya carnosa leaves extract, 1% Chloramphenicol and Ciprofloxacin against Staphylococcus aureus and Pseudomonas aeruginosa. Based on inhibition zones and MIC values, Ciprofloxacin showed the most powerful antibacterial activity with mean rank of 13. Chloramphenicol showed a mean rank of 8, and H. carnosa leaf extract showed a mean rank of 3. (13)

Counterpoint
Can plants control indoor air pollution? Recent reports in the media and promotions by the decorative houseplant industry characterize plants as "nature's clean air machine", claiming that National Aeronautics and Space Administration (NASA) research shows plants remove indoor air pollutants. While it is true that plants remove carbon dioxide from the air, and the ability of plants to remove certain other pollutants from water is the basis for some pollution control methods, the ability of plants to control indoor air pollution is less well established. Most research to date used small chambers without any air exchange which makes extrapolation to real world environments extremely uncertain. The only available study of the use of plants to control indoor air pollutants in an actual building could not determine any benefit from the use of plants69. As a practical means of pollution control, the plant removal mechanisms appear to be inconsequential compared to common ventilation and air exchange rates. In other words, the ability of plants to actually improve indoor air quality is limited in comparison with provision of adequate ventilation.
• While decorative foliage plants may be aesthetically pleasing, it should be noted that over damp planter soil conditions may actually promote growth of unhealthy microorganisms.
(4)

Availability
Ornamental cultivation.

© Godofredo U. Stuart Jr., M.D. / StuartXchange

Updated July 2018 / May 2015

Photos © Godofredo Stuart / StuartXchange

Additional Sources and Suggested Readings
(1)
Study identifies best air-purifying plants / Sharon Dowdy / University of Georgia / College of Agricultre and Environmental Sciences
(2)
Determination of Volatile Compounds from Hoya carnosa Flowers (Aslepiadaceae) / Jankana Burana-osot and Gerhard Buchbauer / Thai J Pharm Sci. 26 (1-2):39-44 (2002)
(3)
Indoor Air Pollution: An Introduction for Health Professionals / Can plants control indoor air pollution? / Environmental Protection Agency
(4)
ADPglucose Pyrophosphorylase from the CAM Plants Hoya carnosa and Xerosicyos danguyi. / Singh BK, Greenberg E, Preiss J. / Plant Physiol. 1984 Mar;74(3):711-6.
(5)
Malate metabolism in Hoya carnosa mitochondria and its role in photosynthesis during CAM phase III
/
Hoang Thi Kim Hong, Akihiro Nose*, Sakae Agarie and Takayuki Yoshida / Journal of Experimental Botany Volume 59 Issue 7Pp. 1819-1827
(6)
Oligosaccharides from Hoya carnosa / Kazuko Yoshikawa,* Hiromi Nishino, Shigenobu Arihara, Hsen-Chang, and Jen-Der Wang / J. Nat. Prod., 2000, 63 (1), pp 146–148 / DOI: 10.1021/np990368d
(7)
Haemolytic crises caused by Hoya carnosa in a patient with G6PD deficiency. / Kuliszkiewicz-Janus M, Tyran W, Szajerka G / Acta Haematologica Polonica [1992, 23(1):63-67]
(8)
Hoya carnosa (L.f.) R.Br / Synonyms / The Plant List
(9)
Hoya carnosa extracts and methods of use US 8865231 B2 / Patents
(10)
Hoya carnosa / Wikipedia
(11)
Circadian rhythmicity of nectar secretion in Hoya carnosa / Philippe Matile / Botanica Helvetica, June 2006; 116(1): pp 1-7 / DOI: 10.1007/s00035-006-0740-4
(12)
Many Hoya varieties / GardenNerdy
(13)
Antibacterial Activity  Extract Hoya Carnosa Leaves, Chloramphenicol 1% and Ciprofloxacin Against Staphylococcus Aureus and Pseudomonas Aeruginosa that Caused Benign type Chronic Suppurative Otitis Media (Disc Diffusion Method) / Made Lely Rahayu, Komang Andi Dwi Saputra and Eka Putra Setiawan / Biomedical and Pharmacology Journal, 2017; 10(3) / DOI :  http://dx.doi.org/10.13005/bpj/1249
(14)
Circadian rhythmicity of fragrance emission in flowers of Hoya carnosa R.Br. / Rolf Altenburger and Philippe Matile / Planta (1988); 174: pp 248-252

It is not uncommon for links on studies/sources to change. Copying and pasting the information on the search window or using the DOI (if available) will often redirect to the new link page.

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