Thursday, April 10, 2008

Anthurium aristocracy


The anthurium is a uniqueornamental plant that has beendubbed the aristocrat of the plantworld, commanding attention andgenerating considerable interestwherever it is displayed. Its estimatedworld trade exceeds US$20 million. This places it second in trade andeconomic value only to sprayorchids, and makes it a thrivinglucrative industry in many parts ofthe world, including severalCaribbean countries, Taiwan,Singapore, Thailand, Japan, and thePhilippines. However, Hollandremains the world's largest grower,and by virtue of its extensivebreeding programme, this country isthe primary source of new coloursand cultivars to the internationalmarket. While Holland suppliesmainly the European market, Hawaiiremains the chief supplier to theUnited States, and over the yearshas developed as the epicentre forpublished research on variousaspects of anthurium genetics,propagation and improvement.Recently, the anthurium has been apopular feature in the ornamentalarena of New Zealand and Australia.There is a uniquely strong market forthe anthurium as a pot plant in boththese countries, whereas in manyother countries the predominanteconomic focus is the cut flowerindustry.The genus Anthurium belongs to thefamily Araceae, which includes otherwell known ornamental genera, suchas Spathiphyllum, Zantedeschia,Philodendron, and Monstera. Whilethe taxonomic literature describesas many as 1,000 Anthurium species,A. andraeanum Linden is widelyaccepted as the progenitor of theanthurium cut flower cultivarscommercially propagated today, andis the highlight of this article. Sinceits discovery in Colombia it has beenbred and cultivated extensively forits brilliantly coloured and patternedflowers. However, A. andraeanumitself represents a hybrid population,and the wide variation in size, colour,and growth form of anthuriums incultivation is a consequence ofextensive interspecific hybridisation.Anthurium flowersThe term "flower" is used to refer tothe commercial product, made upof the spathe, spadix and peduncle(flower stalk). The anthurium spatheis actually a modified bract thatsubtends the protruding cylindricalinflorescence rachis, called thespadix (Higaki et al., 1984). Thesurface of the spadix is made up offused segments, each being the pointfrom which the true flower emerges.The true flowers are minute,hermaphroditic and protogynous (thefemale parts of the flower developfirst) in development, makinganthurium highly outcrossing(Campbell, 1900). The flowers areinvisible to the naked eye and areinsect pollinated. Once fertilised theovary enlarges and forms a singleberry with one or two seeds inside,in a process that completelydisfigures the spadix. Once mature,these detach from the spadix.The growth of the anthurium plant isdivided into a juvenile phase,followed by a generative orreproductive phase. In the juvenilephase, vegetative buds emerge inthe axils of the leaves, while in thegenerative phase, inflorescence budscan be found in the leaf axils(Christensen, 1971). Once thejuvenile phase has passed, flowersare produced in an alternating cyclewith leaves throughout the year(Kamemoto and Nakasone, 1963).When the flower emerges in the leafaxil, the spathe may or may not behighly coloured, but it is tightly curledaround the immature spadix. It takesan average of 6-9 weeks from thetime of its emergence, for thepeduncle to be fully extended andthe spathe fully expanded, exposinga mature spadix. For A. andraeanum,the spathe is cordate and simple,with very prominent veins thatoriginate at the spadix-spathejunction. These run in arcs along thesurface of the spathe, and convergeat its apex (Higaki et al., 1984). Thespathe is also characterised by athick cuticle on the upper and lowerepidermis. The epidermis (both upperand lower) is one cell layer thick, andbeneath this is a single or doublelayer of similar sized, hypodermalcells. In anthurium, flower colourpigment generally accumulates onlyin the hypodermal cells of both theupper and lower epidermis. Vern Collette

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