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POLLEN‐COLLECTING HAIRS OF CAMPANULA (CAMPANULACEAE), I: HISTORICAL REVIEW
Author(s) -
Shetler Stanwyn G.
Publication year - 1979
Publication title -
taxon
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 81
eISSN - 1996-8175
pISSN - 0040-0262
DOI - 10.2307/1219578
Subject(s) - campanulaceae , pollen , biology , pollination , botany , stamen
Summary The literature on the unique pollen‐collecting hairs of Campanula (Campanulaceae) is reviewed as background for new pollination studies, with particular reference to the nature and function of the collecting‐hair mechanism in the breeding system. The main features of the floral mechanism, including the pronounced dichogamy (protandry) and insect adaptation, were first described and depicted accurately by Sprengel in 1793, although pollination observations date back at least to Linnaeus in 1738. Numerous other workers have since added details but little that is basically new to our knowledge of the floral mechanism. Brief reference is made to some of the significant contributions to cytology, cytogenetics, and pollen morphology in recent years. Campanula is basically allogamous, although cases of limited autogamy are known. Experimental studies have shown that campanulas range from complete self‐sterility to complete self‐compatibility, but self‐fertilization usually is accomplished only with difficulty under experimental conditions, and there is little evidence of spontaneous self‐pollination in nature. The pollen is presented from the hairs on the style, which collect the pollen from the anthers while in the bud. The hairs have been known since 1839 to possess the unusual capacity to retract into the style, but the adaptive significance of this mechanism has yet to be explained satisfactorily. The collecting hairs, since before they were known to invaginate, have been interpreted by some investigators as part of a mechanism either to effect fertilization directly through the style without the stigmas or as a back‐up to insure autogamy when cross‐pollination breaks down. Although little evidence exists to support either view, there is still no definitive explanation of their function in the breeding system. Among campanulaceous families, the genera of the Campanulaceae s.str. are believed to have the least advanced (“naked”) form of stylar pollen presentation.