Hoya carnosa, also known as the Wax Plant or Honey Plant, is a climbing perennial native to the tropical lowlands of India, China and Australia (Royal Horticulture Society, n.d.; Missouri Botanical Gardens, n.d.). The name “Hoya” was derived from the late Thomas Hoy, a gardener to the Duke of Northumberland in the eighteenth century (Missouri Botanical Gardens, n.d.). This exotic looking species belongs to the Apocynaceae family, with other members including dogbane and milkweed (Royal Horticulture Society, n.d.; Missouri Botanical Gardens, n.d.). Vines in this family grow counterclockwise around a wire or trellis in a spiral-like pattern (Missouri Botanical Gardens, n.d.).
The wax plant gets its name from the characteristic waxy green elliptical leaves and small, wax coated white to pink coloured flowers (Missouri Botanical Gardens, n.d.). The flowers have a five petal star structure with a red corona in the center and secrete large amounts of nectar, that give them a strong fragrance (Missouri Botanical Gardens, n.d.). Flowers grow in large circular bunches, with clusters contain upwards of thirty flowers (Missouri Botanical Gardens, n.d.).
Nectar secretion in the flower has been found to operate on a biological clock (Altenburger and Matile, 1998; Matile, 2006). Laboratory studies have demonstrated that nectar and fragrance secretion occur at night, producing at maximum around midnight and at minimum during the midday (Matile, 2006). Nectar is known to play an important role in the pollination of plants5. Although nectar is identified to play a role in attracting pollinators, little is known about the pollination process of the wax plant. It is thought to be insect pollinated, specifically by moths, due to nocturnal nectar secretion (Matile, 2006).
This species uses cassulacean acid metabolism (CAM) to metabolize carbon during photosynthesis, which is commonly used in succulent plants (Rayder and Ting, 1983). This method involves keeping the stomata opening on the surface of leaves, where carbon dioxide enters the plant, closed during the day (Rayder and Ting, 1983). Laboratory studies have concluded that water stress induces stomatal closure in the wax plant and therefore CAM (Rayder and Ting, 1983). In this state, growth does not occur, but the plant can remain dormant for extended periods of time (Rayder and Ting, 1983).
Altenburger, R. and Matile, P. (1998). Circadian rhythmicity of fragrance emissions in flowers of Hoya carnosa R. Br. Planta 174:128-252. Retrieved from: http://link.springer.com/article/10.1007/BF00394778
Matile, P. (2006). Circadian rhythmicity of nectar secretion in Hoya carnosa. Bontanica Helvetica. Volume 116, Issue 1, pg 1-7. Retrieved from: http://link.springer.com/article/10.1007/s00035-006-0740-4
Missouri Botanical Gardens. Hoya carnosa. Retrieved from: http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b537
Rayder, L. and Ting, I. (1983). CAM-idling in Hoya carnosa (Asclepiadaceae)*. Photosynthesis Research 4, 203-211
Royal Horticulture Society. Hoya. Retrieved from: https://www.rhs.org.uk/advice/profile?pid=824
WikiCommons. Hoya carnosa flowers. Retrieved from: http://commons.wikimedia.org/wiki/File:Hoya_carnosa_flowers.jpg
Wikipedia. Anexo:Especies de Hoya. Retrieved from: http://es.wikipedia.org/wiki/Anexo:Especies_de_Hoya
Wikipedia. Hoya carnosa. Retrieved from: http://en.wikipedia.org/wiki/Hoya_carnosa