Ascendency is a system indicator used for describing flow characteristics of ecosystems. Experience shows, however, that ascendency is primarily a function of the flow characteristics at the lowest trophic levels. This is because of the way ascendency is calculated: throughput times information content of the flows. Aggregation of groups with low throughput hardly reduces the information content of the flow system, and therefore hardly influences the ascendency. An emergy-based unit is suggested for calculation of ascendency. The calculation procedure is described and it is demonstrated that emergy-based ascendency has the desired properties, notably sensitivity to the flow characteristics of all trophic levels. The use of ascendency, both energy and emergy based, for aggregation of groups in ecosystems is demonstrated, and it is shown that the higher the information content of the flows the less the difference between energy- and emergy-bound ascendency.