Identification by stem-section

The two species are strikingly different in cross-section, and there would be few problems of separation.....

if not for the frequent presence of their hybrid!

By far the best way to learn these differences is to make a cross-section and look for the differentiating features in that.

Download the following comparison
here (350KB JPEG; opens in a new window)

You can download the following three explanatory diagrams below (the labelled ones) as PDFs – these open in new windows; allow a few seconds.

  • T. cespitosum ~ Northern Deergrass (956 KB): PDF
  • T. ×foersteri ~ Hybrid Deergrass (468 KB): PDF
  • T. germanicum ~ Common Deergrass (640 KB): PDF

Hopefully these diagrams will clarify the differences. Let me know if you think it can be more clearly stated.

T. cespitosum ~ Northern Deergrass

Solid’ green tissue with no air-channels; sub-stomatal pits large:

T. ×foersteri ~ Hybrid Deergrass

Intermediate. Green tissue has air-channels (very variable extent); sub-stomatal pits obvious, but rather smaller than in T. cespitosum:

Green tissue has “islands” of clear cells, but very variable in extent (three examples below); but sub-stomatal pits do not vary much in size.
next page (Stem vertical section) for a possible explanation of this pattern.)

Hybrid Deergrass T. ×foersteri : three different sections

T. germanicum ~ Common Deergrass

Green tissue has large air-channels (can be larger than the example below); sub-stomatal pits tiny
(but note some regions of clear cells below stomata: see caption in the diagram):

Links to other pages (also accessible from the sidebar)