Reproduction and variation in Aconitum columbianum (Ranunculaceae), with emphasis on California populations.

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 studied ranges from 3.4 mm (SD = +0.32) to 9.4 mm (SD = +0.75). Correlations of nectary depths with the foraging behaviors and tongue lengths of bees visiting A. columbianum flowers indicate that populations with shallow nectaries are adapted to pollination by both shortand long-tongued bees. Bumblebee species with short tongues are not usually pollinators of flowers in populations with deep nectaries. Nectary depth is geographically correlated in California, and populations over large areas have similar nectary depths. Nectary depth is also correlated with bulbifery. Bulbiferous plants have strictly shallow nectaries, and are confined to two regions near the western extreme of the range of A. columbianum. The range of bulbiferous Aconitum in California is contiguous with the range of non-bulbiferous populations with shallow nectaries. ACONITUM COLUMBIANUM Nutt. in T. & G. is an herbaceous perennial which occurs in the mountains of western North America from Canada to Chihuahua, Mexico. Populations usually are widely separated from one another, cover small areas, consist of many plants growing at high density, and seldom occur below 4,000 feet elevation. Populations usually are found in spring fed bogs, in seep areas, in meadows, or along streams. The flowers have showy petaloid sepals and produce large quantities of nectar which is extracted by bees, moths and hummingbirds. Aconitum of the western United States is known for extreme intraand interpopulation morphological variation, and consequently these aconites have been a taxonomic problem (Munz and Keck, 1968). Most taxonomists have included all Aconitum of the western U.S. (not including Alaska) in one taxon, A. columbianum, while a few have chosen among at least 35 other published names. The primary purpose of this paper is to document extreme interpopulation variation in reproductive morphology (nectary depth and I Received for publication 16 February 1979; revision accepted 4 December 1979. Fieldwork was supported in part by a Sigma Xi Grantin-Aid of Research, and by a stipend provided for summer 1974 by California State University, Chico. Gratefully acknowledged are: Dr. Robbin W. Thorp for emending bee identifications; Dr. J. M. J. de Wet, Dr. Kingsley R. Stern, and Dr. Robert A. Schlising for advice and encouragement; Miss Lillian M. Mayer for assistance with field work and photography; and Dr. Arthur W. Ghent for statistical consulting. bulbifery) among A. columbianum populations in several states, and to document differences in reproductive ecology which result from nectary depth differences. The ecological and evolutionary implications of nectary depth differences are evaluated in the context of the floral biology of A. columbianum, and in the foraging behavior of its bumblebee pollinators. In addition, field work was extensive enough in California to determine geographical patterns of variation in reproductive morphology within that state. MATERIALS AND METHODS-Field studies of morphological variation, flower visitors and vegetative reproduction were conducted in Aconitum populations in California (Brink, 1975), Wyoming, and South Dakota (Table 1) during the summers of 1972-1977. Aconitum voucher specimens are deposited at California State University, Chico (CHSC). Herbarium specimens from throughout the range of A. columbianum were examined at the following herbaria: CAS, JEPS, UC and RM. Geographical patterns of morphological variation in California were determined by mapping locations from herbarium labels (Fig. 8), and verified by extensive field checking of bulbifery and by determination of nectary depth population parameters from field collections. Locations of California populations which were visited but for which quantitative data are unavailable can be found elsewhere (Brink, 1975). Nectary morphology was determined from herbarium specimens by distinguishing popu-