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tasmanian liverworts - fossombroniaceae

Fossombronia species

Fossombronia thallus with mature sporophyte
thallus with sporophytes
Fossombronia perianth with developing sporophyte and rhizoids
sporophyte within perianth
dehiscing Frossombronia capsule
capsule opening
Fossombronia spores
spores
Fossombronia spores
spores with elaters

 

Of the 33 species of the genus Fossombronia in Australia 6 have been recorded for Tasmania; the family includes 2 other genera with single members in the country. We have no idea how common they are on the Blue Tier as these are fairly inconspicuous plants growing on the ground and it is fairly easy to overlook their presence.

It was only through the sheerest of luck that we discovered our first Fossombronia on the Blue Tier. We noticed some growth on the ground near the Crystal Bridge resembling a darker form of Aneura rodwayi and took a sample. This subsequently turned out to be a hornwort but in the photos we noticed a sporophyte that obviously belonged to a liverwort although this was more rounded than what we have been familiar with. A third trip to the site yielded the perianth which belonged to a thallose liverwort. By elimination and from the structure resembling a somewhat crinkled lettuce we were able to ascertain it was a Fossombronia.

Several subsequent trips to the site failed to produce in situ images as the liverwort was growing through hornwort and thallose lichen with only the sporophytes providing any indication of its presence. Finally a month after our initial discovery we noticed another patch of sporophytes with thallus clearly visible and took the first image above.

The second image above shows a sporophyte developing within the perianth as well as rhizoids near the base which provide some of the functions of the root system in vascular plants. Note the absence of branching. Most liverworts we are familiar with have near transparent rhizoids - Fossombronia is an exception with crimson or light brown rhizoids - although they may also be hyaline (colourless). Third image is of capsule opening. Fourth image is of the massed spores and the last is of individual spores together with double and triple helixal elaters which help dispersal. (It is not possible to do justice to opaque three-dimensional material using transmitted light at high magnifications.)

We soon discovered that Fossombronia is a difficult genus to identify to species level using vegetative features which may vary in differing environments. Spore characteristics, on the other hand, are fairly constant and are more reliable for identification.
David Tng tentatively identified this as F. caespitiformis using Scott's book cited below but suggests that use of an electron microscope will be necessary to confirm identification.

It is interesting that at least in the one specimen we observed the dehiscing capsule (pix 3) did not split into quadrants as is common for leafy liverworts but the 'skin' simply fragmented to release the spores. This may be because of prolonged storage under moist conditions before exposure to drier atmosphere.

We came across what could possibly be another species subsequently from Goshen, outside the Blue Tier. This was identified as F. truncata.

Fossombronia species
Fossombronia truncata
Immature capsule
Immature capsule
Fossombronia sporophyte
sporophyte
mature sporophyte
mature capsule
Fossombronia spore
spore, 50 µm across

 

Literature
- Scott, G.A.M. (1985) Southern Australian Liverworts. Australian Flora and Fauna Series Number 2. Australian Government Publishing Service, Canberra

Web
- Utas has a page on Tasmanian fossombronias with plans to develop a key for the genus
- Australian National Botanic Gardens provide a page on sporophyte development of thallose liverworts
- Scanning electron micrograph of Fossombronia wattsii spore
- E. O. Campbell has an interesting but dated (1988) paper on New Zealand fossombronias with SEM images of sporophytes and includes a bibliography

Page URL: http://www.bluetier.org/Liverwort/fossombronicaeae.htm

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