Moss Feet

Did you know that mosses have feet? No joke they do. But they don't use them to walk or run around. And thank goodness, because I am glad that I don't have to go chasing them when I go plant collecting.

Ok, bryophyte feet. At the bottom of the bryophyte sporophyte is the foot. It is the region where the un-branched sporophyte is physically attached to the leafy gametophyte. The foot functions in the transfer of nutrients from the maternal, leafy gametophyte to the sporophyte. These are a couple of good reviews about this region in mosses and across land plants.

Ligrone, R. and Gambardella, R. (1988) The sporophyte-gametophyte junction in bryophytes. Advances in Bryology 3: 225-274. (book)

Ligrone, R., Duckett, J. G. and Renzaglia, K. S. (1993) The gametophyte-sporophyte junction in land plants. Advances in Botanical Research 19: 231-317.

My thinking about bryophyte feet was stimulated by a question from a colleague in my department. They were teaching the students about mosses in the Introductory Biology class and were discussing why in old, mainly brown sporophytes of Polytrichum the foot remains green. Early in development the entire sporophyte is green and photosynthetic. Later in development the capsule and stalk turn brown/red and dry out.

Here are some reasons why I think that the foot may remain green long after the rest is no longer photosynthetic. These are just my hypotheses/ideas. I don't have any data or citations to back them up. (1) It is protected from desiccation by the surrounding leafy gametophyte and thus does not dry out. Resulting in it remaining green and hydrated for longer. AND/OR (2) Since it is involved in nutrient transfer from the leafy gametophyte to the sporophyte, it may remain metabolically active and functioning in nutrient transfer until late in sporophyte development. Being able to function in nutrient transfer would require that this tissue is still alive and maybe also photosynthetic = green.

You can see the foot of a moss sporophyte by gently pulling the sporophyte out of the gametophyte that it is attached to. I honestly only remember trying this on Polytrichum when teaching intro bio. I am definitely going to have to take a look at the feet of other species of mosses to see if they also remain green long after the sporophytes have become brown.