van Geel 1978: The morphology of several three-septate ascospore types (Types 14, 16A, 16B, 16C, 17 and 104) found in section Engbertsdijksveen I was characteristic enough to separate them from one another, but there remains a group of (different) three-septate ascospores in which few distinctive characters could be detected. They were combined in the aggregate Type 20.
Shumilovskikh et al 2015: HdV 20d is characterized by tapering apical ends, in contrast to the three-septate ascospores of HdV 20 (van Geel 1978).
van Geel B (1978) A palaeoecological study of Holocene peat bog sections in Germany and the Netherlands, based on the analysis of pollen, spores and macro- and microscopic remains of fungi, algae cormophytes and anymals. Rev. Palaeobot. Palynol. 25:1-120.