Unique stigmatic structure in three genera of Proteaceae

In three closely related genera of the Proteaceae, namely, Lomatia R.Br., Stenocarpus R.Br. and Strangea Meisn. the pollen presenter and stigma at anthesis are covered by specialised cells. The cells are spiral-walled, contain polyphenolic material and are produced from the stigma, and in Lomatia from the pollen presenter. The spiral wall-thickenings are formed on the inside of the primary wall late in the development of the cells when they are budded off from the stigma or presenter surface. Pollen from the anthers is placed onto these cells from where it is taken to other flowers for cross-pollination. The spiral-walled cells prevent contact between self-pollen and the stigma and provide a method whereby cross-pollen can only reach the stigma if self-pollen has been removed. The form of the cells and the mechanism for preventing autogamy is not found in any other plant group.