POLLEN BRUSH OF PAPILIONOIDEAE (LEGUMINOSAE): MORPHOLOGICAL VARIATION AND SYSTEMATIC UTILITY

The pollen brush commonly is referred to as a “bearded” or “pubescent” style in taxonomic literature and traditionally is taken to be an aggregation of trichomes on the distal end of the style, and occasionally including the stigma. We present data that support the taxonomic utility of the pollen brush but define it more specifically as a dense aggregation of erect trichomes emanating from the style (not stigma or ovary) and functioning in secondary pollen presentation. We recommend avoiding such vague terminology as bearded or pubescent styles as these refer not only to the pollen brush but also to ciliate and penicillate stigmas and ciliate styles. The latter three conditions have some taxonomic use, and since their occurrence is not necessarily correlated with the presence of a pollen brush, they should be distinguished from it. We estimate that the pollen brush has arisen independently in the following eight taxa: 1) Crotalaria and Bolusia (Crotalaraieae), 2) subtribe Coluteinae (Galegeae), 3) Tephrosia subgenus Barbistyla (Millettieae), 4) Adenodolichos (Phaseoleae subtribe Cajaninae), 5) Clitoria (Phaseoleae subtribe Clitoriinae), 6) the subtribe Phaseolinae (Phaseoleae), 7) the Robinia group (Robinieae), and 8) the tribe Vicieae. Its hypothesized homology within each of these groups is supported by a cooccurrence with other taxonomic characters, both morphological and molecular.