Family BRACHYTHECIACEAE

Microhabitat

This epiphytic moss is usually found growing on tree branches, trunks, or stumps and sometimes even on rocks (depending on the growth form) but almost never on the ground.

Distribution

Isothecium stoloniferum is found in western North America from Alaska to California. In British Columbia it is reported frequently in coastal areas and occasionally from the interior.

Branching pattern of a creeping specimen
Photo Credit: Yan Zhuang

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Morphology

This moss species is highly variable. Plants found on rocks and tree bases most often have thick regular branching, while plants growing on tree branches are often slender and hanging. The branching pattern is often untidy, and branches usually emerge at close to right angles from the main branch. The shoots are often attenuate. The leaves are not sharply pointed, and they have toothed margins near the tip and a single, obvious costa (midrib). Sporophytes are often abundant. They are red-brown in colour, and suberect or inclined.

Key identifying features

I. stoloniferum is often epiphytic on all kinds of trees, most often in humid, coastal forests. It tolerates a wide variety of light conditions, but is not likely to be found in deeply shaded areas. The irregular, untidy branching will be the first clue as to the identity of this plant. The plant can grow in up to 4 growth forms which are thought to be influenced by moisture and shade. Sometimes two growth forms will be present in the same specimen. If you realize that you have different growth forms, rather than different species, it will be a great clue that you have Isothecium. Often, the leafy shoots are slender and have a creeping nature. If you look closely with a hand lens at the leaves you will note that they have a toothed margin and a single midrib.

Interesting notes

This is a moss with an identity crisis. It has proven very difficult to classify and name because it has many growth forms that look very different from each other. In fact, there is still some debate about whether these growth forms are all one species or if they should be separated into different species. What this means to an average moss enthusiast is that I. stoloniferum provides an interesting identification challenge.

Isothecium stoloniferum is abundant in its favourite habitats. It drips off of tree branches and trunks, and even adorns rocks occasionally. It is so ubiquitous, in fact, that it was chosen as an indicator species for a heavy metal assessment throughout the lower mainland.

The scientific name Isothecium stoloniferum is quite a mouthful, and might seem difficult to remember at first, but actually the name tells you a lot about the plant if you know a little Greek. In the genus name, iso means equal, and thecium means receptacle or container, which refers to the sporangium. This makes reference to the symmetric sporangia often found in this genus. The specific epithet stoloniferum means “bearing stolons”. Stolon is the botanical term for a shoot that bends to the ground or that grows horizontally above the ground. This makes reference to the creeping nature of the species.

This species is often incorrectly (according to genetic evidence) called Isothecium myosuroides, which is really only found on the Atlantic coast of North America and in Europe. It may also be referred to as I. spiculiferum in books and on the internet, causing even more confusion.

This diverse moss was noticed early in BC’s bryophyte discovery history, and was described by the Swiss-born explorer Samuel Bridel in 1827. It has had over 7 name changes since that time, but the current name has stuck for more than 100 years. However, as mentioned at the start of this section, the many growth forms of this species beg the question of whether they really are all the same species and have been the subject of some genetic research to unravel the answer. With this technology and renewed interest in Isothecium stoloniferum, another name change may be on the horizon.

Selected References

Index Collectorum of the Department of Systematic Botany at the Albrecht von Haller Institute of Plant Sciences, Georg August University Göttingen:
http://www.sysbot.uni-goettingen.de/index_coll/Search_B.htm#B

Pott, U., and Turpin, D.H. 1998. Assessment of atmospheric heavy metals by moss monitoring with Isothecium stoloniferum Brid. in the Fraser Valley, BC, Canada. Water, Air, Soil Pollut. 101(1-4): 25-44.

Lawton, E. 1971. Moss flora of the Pacific Northwest. The Hattori Botanical Laboratory, Ninchinan, Miyazaki, Japan.

Schofield, W.B. 1992. Some common mosses of British Columbia, 2nd ed. Royal British Columbia Museum, Victoria, Canada.

By Sharon Jeffery

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