Leafy spurge (Euphorbia esula) L. is a herbaceous perennial that has flourished as a weed of economic and ecological importance due primarily to its superior reproductive and competitve abilities. Unfortunately, current research on leafy spurge is lacking in all areas but control methodology. Thus, virtually no reproductive studies have been done on this plant. This report is one of a series aimed at understanding the reproductive biology of this economically important noxious weed. Flowers at various stages before and after pollination were collected from natural populations in North Dakota for use in this study. Results of fluorescence and brightfield microscopy indicate that stigmas are typically loaded with numerous pollen grains, but relatively few pollen tubes grow through the stylar tissue. Pollen is tricellular when shed and the transmitting tissue is solid. Tube-like cells comprise a putative obturator that extends into the micropyle. The obturator may facilitate the entry of pollen tubes into the ovule. Results of self-compatibility and apomixis studies will also be discussed. Understanding the reproductive biology of leafy spurge may prove instumental in future methods aimed at controlling the spread of this plant.

Key words: breeding system, Euphorbia esula, leafy spurge, pollen tube