Top: Enlarged sepals are the showy part of the Mussaenda inflorescence. Below: Enlarged portion of top photo showing partly-opened petals of one flower
The mussaendas are a group of highly ornamental shrubs suited to tropical and subtropical climates with a bright future, both as landscape plants and as potted floral decorations.
They're members of the large Rubiaceae family, which also contains Gardenia, Ixora, Pentas and Coffea (coffee).
The most distinctive feature of Mussaenda (and some other genera of the Rubiaceae) is that the floral display is primarily derived from the calyx, with some individual flowers within an inflorescence carrying an enlarged petaloid sepal. Some cultivars have all five sepals enlarged. These are called calycophylls or sometimes semaphylls (that is, a structure which signals a pollinator). In many publications, these are erroneously referred to as bracts.
There are Mussaenda species native to Africa, Madagascar, Asia and the Pacific. Commonly cultivated species include Mussaenda philippica, M. erythrophylla, M. frondosa and Pseudomussaenda flava (also referred to as Mussaenda flava, M. glabra, M. luteola, M. lutea or M. incana in various publications).
University of the Philippines Los Baños has been active over many decades in breeding these ornamentals and is responsible for the popular cultivars 'Queen Sirikit', 'Doña Aurora' and 'Doña Luz'. Many more cultivars have been developed in the Phillipines, although not widely available in Australia.
Many are named after First Ladies and other notable women of the Phillipines, hence the Spanish form of address "Doña" in some cultivar names. 'Queen Skirit' was named after the Queen of Thailand to commemorate a visit to the Phillipines.
Mussaenda can produce seed (in a small fruit), but production is poor and unreliable. Seed is significant for the purposes of hybridising but vegetative methods are used for commercial propagation.
Cuttings can be also be difficult to strike, although this varies among cultivars. Alternative means of propagation include grafting, layering and marcotting. Refinement of methods for mass propagation of the more difficult cultivars (cutting type, growth regulators, incubation conditions, etc) could mean a greater range of cultivars available for purchase in the future.
These soft-wooded shrubs can have some tendency to climb, so depending on pruning they can be kept as shrubs, trained as small tree or allowed to scramble through a nearby tree. They are suitable for full sun or part shade.
The major attractions of mussaendas in the landscape is their extended flowering period. They will loose their leaves and go dormant through the cooler and drier winter, but put on a spectacular display throughout the warm, wet months. If conditions are suitable, they can flower year-round. They have poor drought and cold tolerance.
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'Capricorn Ice' PBR and 'Capricorn Dream' PBR are two Mussaenda cultivars developed by Orams Nurseries in Queensland, Australia
Some species and cultivars have proven to be better performers than others outside of the tropics and local breeding efforts may help improve the popularity of mussaendas in subtopical and warm temperate parts of Australia. Orams Nursery, near Rockhampton on the central Queensland coast, have released two cultivars 'Capricorn Ice' PBR and 'Capricorn Dream' PBR.
In addition to their role in the garden, mussaendas have potential as potted floral gifts. Research in the Phillpines investigating appropriate treatment including growth regulators and selection of suitable hybrids is aimed at developing this market. Given that Mussaendas can bloom year-round in suitable climates, there is presumably no daylength requirement. This gives them a particular advantage over Poinsettia as a floral Christmas decoration in parts of the world where flowering must be artificially induced.
As research and hybridisation work progresses, cultivars with new colours, growth habits, climatic tolerances and amenability to propagation could mean that we'll be seeing more of these these flamboyant shrubs in our lives in the future.
Bibliography and Further Reading:
An extensive list of links to more information about Mussaenda, including publications used in preparation of the article above is based, can be found at www.calyx.com.au/mussaenda.html.
Acknowledgment: Thanks to Orams Nurseries for additional information and images of their cultivars.