Portioned pollen release and the syndromes of secondary pollen presentation in the Campanulales-Asterales-complex )

Abstract

Summary The release of pollen in portions, i. e. limiting the pollen removed by individual pollinators during a single visit, is a widespread phenomenon. The biological significance of this phenomenon is that it helps to optimize the pollination. Parameters like number of ovules, number of application sites to the pollinator or spectrum of pollinators, which may be correlated with the size of the pollen portion, are illustrated as a net of possible correlations (Fig. 1). Apart from pollenkitt, viscin or cellulosic threads and the non-simultaneous opening of the anthers, the secondary pollen presentation is a special mechanism of pollen portioning. Secondary pollen presentation occurs in several dicotyledonous and in a few monocotyledonous families. Its occurrence is a distinctive feature in the Campanulales-Asterales -complex. The different mechanisms in the Campanulales-Asterales ( Asteraceae, Lobeliaceae, Campanulaceae, Goodeniaceae, Brunoniaceae, Calyceraceae ) are briefly described. The differentiations of the basic syndrome (radial symmetry of the flower bud, complete androecial whorl, introrse anthers, the latter connivent at the time of dehiscence, proterandry, late and sequential growth of filaments and style) are presented in two diagrams (Figs. 30 + 31). In addition, a few remarks are given on pollen presentation in Rubiaceae, Cyphiaceae, Sphenocieaceae, Pentaphragmataceae, Stylidiaceae , of which the latter four are usually assigned to Campanulales-Asterales .