phyllotaxy defined in 1951 yearphyllotaxy - phyllotaxy (phyllotaxis);
phyllotaxy - Arrangement of leaves on stem, whorled, opposite, alternate or spiral. In spiral phyllotaxy a line connecting points of attachment of successive leaves forms a spiral. Position of leaves in spiral is regular. In most simple, truly alternate arrangement leaves are 180° apart and to pass from one leaf to that precisely above it involves one circuit of the stem and two leaves, a phyllotaxy of 1/2. Various forms of phyllotaxy occur, 1/3, 2/5, 3/8, 5/13, etc., each fraction representing angle made by successive leaves with stem (looking vertically downwards). At end of each spiral a leaf is directly above the one at the beginning. Looking down on a stem these points of superimposition are identified as vertical rows of leaves known as orthostichies. At growing point, though leaf primordia are spirally arranged, orthostichies do not occur, but looking down at apex, primordia are arranged in a series of descending curves or parastichies, some clockwise, others anticlockwise. Parastichy in an apex, may become orthostichy in a mature shoot by straightening out of spirals during elongation.
near phyllotaxy in Knolik
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