Muriform spores (from Albert Schneider's A text-book of general lichenology)
The word muriform literally means "wall-like". Muriform spores have internal cross walls (or septa) aligned to both the shorter and longer dimensions. When there are many such cross-walls, they give the spore a superficial resemblance to the brick-and-mortar patterning of a brick wall. In the developing spores the walls across the shorter dimension form first. For example, in drawing number 3 you can see a mature spore as well as an immature spore in which only the septa in one direction have formed.
1. Thelotrema lepadinum; 2. Leptogium tremelloides; 3. Lopadium pezizoideum; 4. Mycoporum pycnocarpum; 5. Gyrostomum scyphuliferum; 6. Collema pulposum; 7. Umbilicaria pustulata.
Note: not all to the same scale.
Albert Schneider's A text-book of general lichenology, published in Binghamton in 1897 by Willard N. Clute & Co. illustrates the structural features of various lichens from the north-eastern United States.