Thread-forming structures in angiosperm anthers: their diverse role in pollination ecology

This paper reviews the origin, nature, systematic distribution, and the res pective function of the highly variable and diverse thread-forming structur es in angiosperm anthers (including somewhat similar, rare features in fern s and gymnosperms). On one hand. such threads may function as pollen-connec ting vectors in forming pollen dispersal units, as sporopollenin threads (v iscin threads), e.g. in Onagraceae or sporopollenin-less threads in surpris ingly many other angiosperm families. On the other hand, as is known from t he Impatiens - "pollen basket", threads or ropes may be involved in pollen presentation. In addition, for the first time two new examples of "pollen b askets" in Boraginaceae and Scrophulariaceae are reported. In Echium the ba sket is formed by cellular elements from the modified septal regions, where as in Esterhazya a similar effect is achieved in an analogous manner by tri chomes of the epidermal layer of the thecal wall. There is obviously a diff erent function of these seemingly very similar baskets: in Echium the featu re acts preferably as a pollen presentation agent, whereas in Esterhazya th e primary function is to prevent all the pollen from being dispersed too so on.