Date of Award


Degree Type


Degree Name

Master of Science




Dr. J.B. Phipps

Second Advisor

Dr. R.G. Thorn

Third Advisor

Dr. D. Fahselt


Inflorescence bracteoles of Crataegus (Rosaceae) were investigated with the following objectives: i) to determine the taxonomie significance of bracteoles in Crataegus; and ii) to perform a pilot study on the functions of Crataegus bracteoles. The former was accomplished by a morphometric analysis using 25 bracteole characters from 75 species of Crataegus and 3 outgroup taxa. The latter was accomplished by experiments and observations on bracteole-ant interactions, exudate collection and analysis, and cell organelle staining. These studies revealed: (1) two significantly different bracteole types occur, a symmetric kind found in all species and an asymmetric kind found only in Asiatic species; (2) there is considerable variability in texture, size, width, venation, hairiness and glandularity within the symmetric kind; (3) bracteole data are strongly supportive of existing taxonomy; (4) gland-margined Crataegus bracteoles are the site of extrafloral nectaries that serve to decrease the number of floral visits made by ants.



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