Weissia levieri does not currently have an account in the Field Guide as it is a very rare species and possible to confuse with several other members of Weissia section Astomum (species with perichaetial leaves longer and broader than stem leaves and, usually, capsules immersed in the leaves). Des Callaghan’s excellent Journal of Bryology paper about this group has done a lot to demystify them and includes a key that works well.
W. levieri and its close relatives cannot be safely identified unless mature or near-mature capsules are present. That’s because the presence (or not) of a zip-like layer of small, strongly differentiated cells at the top of the capsule is needed to follow the key. W. levieri has such a layer (see images below) and when the spores are mature, it unzips to release them. W. angustifolia also has it and then it is essential to compare the upper perichaetial leaf margins – involute and narrow-looking in W. angustifolia but plane (or slightly incurved) in W. levieri.
Weissia wilsonii, W. longifolia and W. sterilis all lack the layer of abscission cells in the capsule.
The capsules of W. levieri typically mature in March and April, so that’s the best time to search for it.