This moss was common along the RR tracks in Powell, Franklin County, Ohio during mid-May. 

As in the Platygyrium example, we'll use the key in Howard Crum's 2004 book,  Mosses of the Great Lakes Forest, 4th ed. (The University of Michigan Herbarium. Ann Arbor, Michigan) to figure it out.

But for simplicity we'll skip a few steps of the key. Why? Although the Crum key is terrific, like all traditional keys it can be cumbersome to use. Being dichotomous, keys need to break everything down into two categories, even though the traits under consideration may actually have several variants. For example, leaf cells aren't just either smooth or bumpy, since bumpy ones can be bumpy in many ways: unipapillose with papillae over the lumen, unipapillose by means of projecting end cells, pluripapillose, mamillose, etc.. The result is that when, for example, you're keying out a straightforward papillose-leaved plant, you might get asked what seems like the same "Are the leaves papillose?" question over and over, but asked slightly differently each time.

Keys can also be ineffective, for two main reasons:

(1) Keys use selected characters to chart a path, step by step, to the answer. Often though, plants have one or more very distinctive traits that would narrow them down early and easily, if only the key asked about them. A good example is propagula. When present asexual reproductive structures are often quite obvious, and could help a lot when wading through a mass of otherwise indistinctive pleurocarps. But they may only get mentioned at tail end of the keying path.

(2) Oftentimes the plants are in a stage of dcvelopment where the asked-about feature (something having to do with peristome teeth, for example) is altogether absent. 

There are some improvements to relying solely on keys:

(1) OMLA member Diane Lucas and Malcolm Sargent have analyzed the moss flora of North America and created a very useful Perspective Oriented Guide to Moss Genera that uses readily apparent features to sort the mosses into smaller groups where each of the members included in a single group is defined by one to three major characteristics. 

(2) Interactive keys: Computer-based keys enable users to enter character-state in response to software prompts that enable one to possibly arrive at an answer with whatever array of information is on hand. These have been developed for some organisms, but not Ohio mosses. As yet, the methodology hasn't been standardized, and the more powerful software products are rather expensive.

Note: Some members of OMLA are interested in developing interactive keys to Ohio taxa. If you're interested in working on this project, please contact us.

Back to the mystery moss. It has short upright stems standing side-by-side with sporophytes emerging from their tips, i.e., it is an acrocarp.