Shuttleworth A., Johnson S. D., Jürgens A., Entering through the narrow gate: A morphological filter explains specialized pollination of a carrion-scented stapeliad, Flora, 2017, 232:92-103, doi: 10.1016/j.flora.2016.09.003
The field study of Orbea lutea subsp. lutea combines fly observations, morphometry, scent analysis and measurements of pollination success. In the population studied, pollinia were carried by females of one Atherigona species whose heads fitted between the corona lobes. The paper shows how a mechanical pollinator filter works.