VARIATION IN THE POLLINARIA,ANTHERS, AND ALAR FISSURES OF COMMON MILKWEED (ASCLEPIAS SYRIACA L.)

We measured 10 characters of pollinaria, anthers, and alar fissures from the flowers of seven clones of common milkweed Asclepias syriaca L. to test whether significant differences existed among them. Strong among-clone differences existed for most of these characters. However, these differences were not correlated with each other, except for width of the alar fissure and width of the translator arm. Thus, these floral structures vary mostly in shape, rather than size per se. Few correlations among characters occurred at a within-clone level. Clones growing in the open and shade differed in half of the characters measured, but habitat did not substantially change the among-clone size patterns observed. The alar fissure–translator arm relationship might promote differential uptake of pollinia; however, A. syriaca does not exhibit a clear separation into donor and recipient clones.