This is an uncommon species of good quality calcareous grassland and resembles a rather stunted form of Thuidium tamariscinum. It is more strictly calcicole than T.delicatulum but like that species the branches are not so clearly complanate as in T.tamariscinum. In practice a Thuidium in the preferred habitat that is not typical T.tamariscinum should be examined more closely. The closely related Abietinella abietina grows in very similar habitats but is simply pinnate rather than bi- or tri-pinnate.
T.assimile has stem leaves that when dry often have a reflexed tip but this is not constant and many stems may need to be examined. Microscopically, the row of single cells ending in single long cell at the apex of the stem leaves is the most straightforward distinguishing character, but it can be difficult to distinguish microscopically from T.delicatulum.
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