Sonchus arvensis var. glabrescens Wimm. and Graeb. is at present sparsely distributed in Iowa. The patches are often miles apart. In a number of isolated colonies observed in Clay, Palo Alto, Osceola, Dickinson, Story and Hamilton counties seeds are seldom or never found from July to September. Some tests made relative to the fruiting habits of the Smooth Sow Thistle produced the following results. Self or close pollinated flowers from the same head or from heads in the same colony produced no fruits ("seeds"). Flowers cross-pollinated by brushing with flowers from a distant colony produced almost as many seeds as there were flowers in the head. The heads average about 200 flowers each.
Proceedings of the Iowa Academy of Science
©1937 Iowa Academy of Science, Inc.
"Notes on Seed Production in the Smooth Perennial Sow Thistle,"
Proceedings of the Iowa Academy of Science, 44(1), 105-105.
Available at: https://scholarworks.uni.edu/pias/vol44/iss1/20