Armbruster, W. Scott, Pérez-Barrales, Rocio, Arroyo, Juan, Edwards, Mary E. and Vargas, Pablo
Three-dimensional reciprocity of floral morphs in wild flax (Linum suffruticosum): a new twist on heterostyly
New Phytologist, 171, (3), . (doi:10.1111/j.1469-8137.2006.01749.x).
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• Here, we studied the floral morphology and pollination of the distylous plant
(Linaceae) in southern Spain.
• We observed a previously unreported form of distyly that involved twisting and
bending of styles and stamens during floral development to achieve three-dimensional
reciprocity of anthers and stigmas in the long-styled (pin) and short-styled (thrum)
morphs. This developmental pattern causes pin pollen to be placed on the underside
flies (Bombyliidae), and thrum pollen to be placed on the top of
the thorax and abdomen. The pin stigmas contact the flies on the dorsum, apparently
picking up predominantly thrum pollen, and the thrum stigmas contact the flies on
the ventral surface, apparently picking up predominantly pin pollen.
• This form of heterostyly would appear on morphological grounds to be far more
efficient in dispersing pollen between compatible morphs than the typical pin–thrum
system. If so, this plant fits Darwin’s prediction of efficient pollen flow between
heterostylous morphs more closely than anything Darwin himself reported.
• Molecular phylogenetic analyses indicate that this form of heterostyly evolved in
a lineage that already had typical heterostyly. The analyses also indicate that there
have been several independent origins of heterostyly in
and at least one
reversal to stylar monomorphism.
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