Technical Abstract: Quinoclamine is used in Europe, and was under evaluation in the Unites States for the control of liverwort (Marchantia polymorpha L.) in nursery crops. Liverwort is a non-vascular, chlorophyll-containing plant that can be problematic in greenhouse and nursery crops. POST-applied quinoclamine controls liverwort. However, liverwort structures varied in their sensitivity to POST-applied quinoclamine. Specifically, archegonial receptacles (female) are much more tolerant of quinoclamine than either antheridial receptacles (male) or thalli (leaf-like structure). A series of studies were conducted to first, document the degree of differential sensitivity between tissues to quinoclamine. And secondly, attempt to determine the basis of this differential sensitivity. From a dose response, the LD50 of antheridial receptacles and juvenile thalli were estimated to be 1.60 and 1.27 kg/ha, respectively. The LD50 of archegonial receptacles could not be estimated, but exceeded 10.45 kg/ah. Chlorophyll content varied between liverwort tissues, but the content did not correlate to quinoclamine sensitivity. Absorption as determined with 14C-quinoclamine was less in archegonial receptacles than in either antheridial receptacles or thalli. Scanning electron microscopy of the surface of the liverwort tissues revealed that archegonial receptacles had smaller and fewer pores (equivalent to stomata in higher plants ) than either antheridial receptacles or thalli. We conclude that the tolerance of archegonial receptacles to quinoclamine can be partially, but no exclusively, attributed to reduced absorption. And this reduced absorption can be attributed to the limited porosity of the archegonial receptacles.