by Piter Kehoma Boll
It’s time to go back to the tiny ones, the mosses. The third species of this group to be featured here is called Tetraphis pellucida or the pellucid four-tooth moss. Found in the northern hemisphere, this species is common in deciduous forests and grows almost exclusively on decaying wood of coniferous trees.
The pellucid four-tooth moss can have two different modes of reproduction: sexual and asexual. The sexual reproduction occurs in a way similar to that found in most mosses. The asexual one, however, is somewhat peculiar and happens through the production of propagules called gammae. Gemmae can occur along a stalk, being called stalk gemmae, or inside a cup formed by three to five large leaves, a structure called gemmae cup. Gemmae from both stalks and cups are propelled by the power of raindrops. What is interesting is that the type of gemmae structure seems to be related to the inclination of the surface in which the moss grows. From a horizontal surface to one with an inclination of about 18°, cups are more common, possibly because a water drops falling inside a cup propels the gemmae with great speed upward. On surfaces with inclinations above 18°, stalks are more common, as a cup lying on its side wouldn’t be very useful, and water can wash down gemmae from stalks more easily.
Regarding dispersal, spores from sexual reproduction seem to be able to move farther away from the mother, but they are not as successful in germinating and occupying a new substract as gemmae. Thus, the different reproduction modes seem to help this amazing little moss to spread by adapting to the most adequate means.
However, when other moss species arrive at the substrate, the pellucid four-tooth moss is rapidly replaced. It has, therefore, a very low success when competing with other species. How can it be one of the most common species in its habitat then? Well, it is so because the specialized propagules of the pellucid four-tooth moth allow it to quickly colonize newly-formed substrates, which arise from the common disturbances on the forest floor. No other species can colonize that quickly, but as they can easily dislodge our fellow, there is an endless struggle to survive. The pellucid four-tooth moss relies on disturbance to go on.
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Kimmerer, R. W. (1991) Reproductive ecology of Tetraphis pellucida. I. Population density and reproductive mode. The Bryologist 94(3): 255-260. https://doi.org/10.2307/3243962
Kimmerer, R. W. (1991) Reproductive ecology of Tetraphis pellucida. II. Differential Success of Sexual and Asexual Propagules. The Bryologist 94(3): 284–288. https://doi.org/10.2307/3243966
Kimmerer, R. W. (1993) Disturbance and dominance in Tetraphis pellucida: a model of disturbance frequency and reproductive mode. The Bryologist 96(1): 73-79. https://doi.org/10.2307/3243322