Disa flowers
The drawing on the right shows the main parts of the Disa flower as seen from the front. The biggest parts of the flower are the three sepals. The lip is often very small, especially in the case of the evergreen Disas.The equilateral triangle defined by the tips of sepals is the "ideal" shape of a Disa flower, as laid down by orchid judges in South Africa some years ago. This means that the sepals should be of equal length; moreover the sepals should be wide in relation to their length, and they should not be reflexed. The flower as a whole should be relatively flat, rather than cup-shaped.
A species like D. cardinalis can never be expected to achieve the equilateral proportions as the lateral sepals are always narrow, and longer than the dorsal. However the other species, and most Disa hybrids, can produce flowers shaped close to the ideal. The color of Disa flowers depends on two predominant types of pigment, anthocyanins and carotenoids. Anthocyanins are water-soluble, are present in the surface layer of cells, and are responsible for red, orange and pink colors. Carotenoids are an entirely unrelated class of pigments. They are oil-soluble, lie in subsurface cells, and contribute yellow color. The cells are shown in cross-section in the illustration on the right. In D. uniflora, the carotenoid pigment usually shows up most strongly in the petals. A flower with no anthocyanins would be pure yellow; one with neither type of pigment would be pure white. In the dorsal sepal of D. uniflora the anthocyanins are present in a pattern of attractive veins. In D. tripetaloides and D. aurata the dorsal markings are in the form of spots rather than veins. |
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