Freitag, 14. März 2014

Plant of the Day (March 14th, 2013) - Bryum barnesii J. B. Wood.

In my last post, I presented you Bryum argenteum; a very common moss. This time, I want to show you another moss, which is also very common in cities and everywhere else. This species is Bryum barnesii J. B. Wood., which is also a member of the Bryaceae, of course. In German, the species is known as “Zweifarbiges Birnmoos” and in English as “Bicolored Bryum”.

Please Note: the exact status of B. barnessii as species is still unclear. In many books and publications, the species is threatened as a variety of Bryum bicolor and part of a larger Bryum bicolor complex. As a result, the information in this article also apply for B. bicolor.

1) Description

B. barnesii is a small moss, which can reach heights between 1 and 1.5 centimeters. The species grows in loos turfs or cushions. The small leaflets are only about 2 millimeter long. A clearly protruding leaf-rip originates from the base over the entire leaflet to the tip. Unlike B. argentum, there are no different kind of leaflets and also no chlorophyll-free, glassy tip.

B. barnesii - between two concrete slabs

The Sporophyte of B. barnesii is inconspicuous. The brown seta is only about 15 millimeters long. The egg-shaped capsules with the spores are pendulous and pass abruptly into the seta. Normally, the sprophyte is created during autumn

B. barnesii - habitus

However, the distinctive character of B. barnesii are the Gemmae. In Bryology, a gemma is a instrument of asexual reproduction. Normally, a Gemma consists of a single cell or is a tissue, which is splitted off the plant and grows up as a new individual plant. This kind of reproduction is very useful, if the plant has no sexual partner but has to reproduce in order to survive harsh times.

 B. barnesii - closer look on the shoots

In the case of B. barnesii, the Gemmae are small bulbs, which are located in the axil of the leaflets. A single shoot of B. barnessi has 5 of the Gemmae, which are all located at the top of the shoot. However, 11 Gemmeae are also possible. In contrast to this, B. bicolor has often not a single Gemmae or only one on some shoots. For some scientists, this high number of Gemmea is enough to declare B. barnessi as a new species. Other researchers think that the high number of Gemmae is only a variation of B. bicolor but not an own species.

2) Distribution

B. barnesii is a cosmopolitan and very common in the most parts of the world. It prefers fresh but also bright places and a chalky surface to grow. The species is weak in competition with other plants. As a result, it avoids competition and grows on ruderal wastelands, concrete slabs or even wall cracks.

 as with many other mosses an urban area
is the typical habitus of B. barnesii

In many cases, the species grows together with B. bicolor of B. argenteum

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