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Wednesday, July 25, 2012

Cavernous Crystalwort (Riccia Cavernosa)

Bryophyte
I found this growing on a rock in the Olifants River a long while back and have never been able to identify it. It is about 2.5cm in diameter and a type of Liverwort. A very nteresting find for me.
Thanks to Nigel from http://www.ispot.org.za for telling me what it is.
 What is a liverwort?



A liverwort is a flowerless, spore-producing plant - with the spores produced in small capsules. The introductory WHAT IS A BRYOPHYTE? page noted that bryophytes have a gametophyte stage and a sporophyte stage. The spore capsule (possibly with a supporting stalk, or seta) is the sporophyte and this grows from the gametophyte stage.


The aim of this page is simply to describe the features you can see in a liverwort. You will see much, but by no means all, of the variety to be found in the liverworts. While the identification of liverworts often requires the use of a microscope, you can learn a lot just by using your eyes and a hand-lens that magnifies 10 times. In the reference button you’ll find some books with good colour photographs of Australian liverworts. Looking through them will give you a good introduction to liverwort diversity.


The division of the liverworts into leafy and thallose is very useful and is used by all bryologists. However, it is important to note that there are a few liverworts, classified as thallose, which come very close to leafy in appearance. The liverworts show a great variety of gametophytic form (far greater than that shown by mosses or hornworts). Regardless of whether a liverwort is leafy or thallose, the gametophyte is the dominant stage - in terms of both bulk and longevity. Sporophytes are fairly ephemeral. This is markedly different to the flowering plants where the sporophyte is the dominant stage.


All liverworts produce mucilage, which helps liverworts absorb and retain water. The mucilage is produced by the gametophytes, either internally in slime cells or externally in slime papillae. The latter are simply very tiny outgrowths, possibly stalked, from the gametophyte. Amongst the thallose liverworts there are genera (such as Riccardia, right) in which the mucilage is produced by slime papillae and genera (such as Marchantia) with internal slime cells. In the leafy liverworts mucilage is produced in slime papillae, which may be found on stems or leaf tips, depending on the species. Liverworts produce mucilage at the growing points and this mucilage protects the growing points from drying out.


Since liverworts are photosynthesizing plants, their cells contain chloroplasts. In addition to chloroplasts, the cells of about 90% of liverwort species contain oil bodies . These vary in size, shape and number per cell, depending on species and are therefore useful for identification. While often colourless, brown and blue oil bodies are also found. There are species in which the oil bodies are found in the majority of cells, while in others they are confined to isolated cells. In some cases the oil bodies are persistent and can be found in dried, herbarium specimens but in many species the oil bodies disintegrate when a specimen is dried for storage in a herbarium and the oil bodies are then permanently lost. The compounds found in these oil bodies are various terpenoids and the amount produced various between species. In many cases the functions of these compounds are unknown, but they do give distinctive aromas or tastes to various liverworts.


Another feature common to virtually all liverworts is the presence of rhizoids. These are anchoring structures, superficially root-like, but without the absorptive functions of true roots. Liverworts in the genus Haplomitrium lack rhizoids and have a rhizome-like growth, with both erect and subterranean stems. As a rule liverwort rhizoids are single-celled, with just a few species having multi-celled rhizoids.


The male and female gametes (sperm and eggs) are produced on the gametophyte (in antheridia and archegonia, respectively) and a fertilized egg will develop into a spore-bearing sporophyte. Thus the spores are part of the sexual reproduction cycle. There's more about this in the REPRODUCTION SECTION.

Information from: http://www.anbg.gov.au/bryophyte/what-is-liverwort.html