Thank you to Connor Fitzpatrick for today’s write-up. Just a small update re: Connor — he completed his work-study position here at the garden a couple weeks ago, and moved on to a summer job in Alberta. Best of luck to him! Connor writes:
Today’s Botany Photo of the Day features a moss commonly found in the Nitobe Memorial Garden. The photograph is courtesy Michelle Fitterer.
Polytrichum juniperinum can also be found in the E.H. Lohbrunner Alpine Garden of the UBC Botanical Garden. Previously, Daniel had mentioned that members of the Polytrichidae possess a well differentiated stem anatomy capable of transporting water and nutrients. Another interesting feature of this group is the presence of lamellae.
Lamellae are unistratose (one cell layer thick) flaps of tissue found on the upper leaf surface of many polytrichid mosses. The UBC BIOL 321 website proves to be (yet again) a fantastic resource when it comes to examining moss morphology. Scroll down the page to find a cross-section of a leaf. The lamellae are made up of chlorophyllose cells arranged in flaps to increase the available area for photosynthesis. A cuticle can be found at the top of the lamellae preventing water from leaving and entering the leaf surface. This is adaptive, because too much water in the microenvironment of the leaf surface would hinder gas exchange required for photosynthesis and the loss of water would quickly lead to dessication.
The severely recurved leaf margins, visible in the leaf cross-section and in the photograph, also prevent water loss. This feature in addition to the lamellae and the stem’s conduction ability allow members of the Polytrichidae to tolerate very exposed sites. This tolerance is reflected by Polytrichum juniperum‘s cosmopolitan distribution.
The mosses, as well as the other bryophytes (liverworts and hornworts), represent the first plant colonizers of land and are an understudied group of organisms. In fact, it is still being debated as to whether the bryophytes evolved from a single ancestor or are each of a separate lineage. As there is probably at least one bryophyte adapted to every kind of plant stressor, it’s surprising that more work isn’t being done to understand the evolution and adaptive strategies of this incredibly diverse group of organisms. In Phylogeny and diversification of bryophytes, Shaw and Renzaglia provide a bird’s-eye view of bryophyte phylogeny.