Original: "You can't see the achenes, but I did look at them. They were light brown, just over 1mm in length, and with a small differentiated tubercle nearly as wide at its base as the achene but only about 1/5 the length of the body of the achene."
I looked at more material, most tubercles are about or just over 1/4 the length of the achene and not depressed on their shoulders.
soft round hollow stems about 18" tall. growing in roadside ditch with septic effluent
Eleocharis obtusa is a species of spikesedge known by the common name blunt spikerush. This plant is widely distributed across Canada and the United States, where it grows in wet areas such as riverbanks and moist forest floors. It is also a weed of rice paddies, especially when the rice plants are young sprouts. This is an annual spikesedge approaching half a meter in maximum height. It has many green cylindrical stems which are erect but...