Biosystematic and Ecological Investigations on Tuberous Aconitum (Ranunculaceae) of the United States
Brink, Donald Eben, Jr.
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Permalink
https://hdl.handle.net/2142/68208
Description
Title
Biosystematic and Ecological Investigations on Tuberous Aconitum (Ranunculaceae) of the United States
Author(s)
Brink, Donald Eben, Jr.
Issue Date
1981
Department of Study
Plant Biology
Discipline
Botany
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Language
eng
Abstract
Nectary depth in Aconitum columbianum Nutt. in T. & G. shows little variation within populations but much continuous variation among populations. Mean nectary depth in populations ranges from 3.4 mm (SD = (+OR-)0.32) to 9.4 mm (SD = (+OR-)0.75). Nectary depth is geographically correlated, and populations over large areas have similar nectary depths. Bulbiferous populations have strictly shallow nectaries and are confined to two regions near the western extreme of the range of the A. columbianum complex. Correlations of nectary depths with the foraging behaviors and tongue lengths of bees visiting A. columbianum indicate that nectary depth differences adapt populations to different pollinator types. Populations with shallow nectaries are adapted to pollination by both short- and long-tongued bees, whereas bumblebee species with short tongues are not usually pollinators of flowers in populations with deep nectaries. In A. columbianum there are extreme interpopulation differences in rates of nectar secretion per flower. Nectar sugar concentration varies little among populations, so increased nectar secretion results in a greater mass of sugar per flower for pollinator attraction. Differences in the amount of reward offered per flower account at least in part for observed higher levels of pollinator activity in populations with high nectar production. Nectar production is correlated also with nectary depth, i.e., flowers in populations with deep nectaries have higher rates of nectar secretion than those with shallow nectaries. In conclusion, there are basic differences in pollination ecology among geographical races of A. columbianum which are indicated by correlated interpopulation differences in (1) nectar production, (2) level of pollinator activity, (3) nectary depth, and (4) pollinator-type. There are consistent differences in tuber morphology between Aconitum columbianum Nutt. of the western United States (tubers contiguous) and Aconitum uncinatum L. of the eastern U.S. (tubers separated by elongate connectives). Aconitum populations which occur in Iowa, Wisconsin, Ohio and New York were previously classified as a distinct species (Aconitum noveboracense Gray), or as a subspecies of A. uncinatum, but the populations I studied in Iowa and Wisconsin are closely related to and probably conspecific with A. columbianum. These populations have contiguous tubers and are morphologically indistinguishable in other respects from those races of A. columbianum which are non-bulbiferous and have shallow nectaries.
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