"Some of nature's most exquisite handiwork is on a miniature scale,

as anyone knows who has applied a magnifying glass to a snowflake."

    Rachel Carson (1907-1964)

    Ecologist, writer

Liverwort sporangia, species undetermined. Maricao State Forest, western Puerto Rico.

    Before I begin to show and discuss the things living in the Caribbean, I should offer a cautionary comment on the field of biology that deals with the diversity of life: Systematics. This branch of Biology is usually divided into two areas: Taxonomy (which deals the classification and naming of biological organisms), and Phylogenetics (which deals with the evolutionary relationships between organisms). And my remarks are cautionary, more than anything else, because I am not a biologist. I am only playing at being one.

    The classification of biological entities is in a state constant fluctuation, because it is in its nature to be fluctuant. As one moves down the branches and the trunk toward the roots of the phylogenetic tree of life, and approaches the lower levels of classification, the distinctions among plants, animals, fungi, and hosts of unicellular organisms become increasingly blurred. While I have tried to be as scientifically precise as possible, this web site is not about Systematics, and I deal only with its very basics, when I have to.

    Indeed, because Taxonomy and Phylogenetics do not exactly correspond to one another even when treating the same subjects, they are sometimes difficult to integrate.

    For all the advances of modern Biology, it is still difficult at times to emplace some organisms among animals, or plants, or fungi. Today, for example, the very term "plant" has rather little value, from a strictly scientific standpoint. If we were to limit the concept involved therein to terrestrial photosynthetic organisms and some (not all) groups of green algae, and were then to become fastidious in distinguishing them from other creatures, we should speak not of "plants", but of the "phylum Virideplantae" within the "kingdom Eukariota".

    Then you have fungi, a taxonomic kingdom unto themselves, and thus on a par with other eukariotes like Viridaeplantae (green plants), Metazoa (animals), Rhodophyta (red algae), and several others. Considered to be plants until the late XX century, they are now believed to be more closely related to animals than to any other group of living beings.

    So, you see, for all its "cold scientific objectivity", Taxonomy (and, really, empirical sciences in general) is as much an art as it is a science. It depends on strict observation, experimenting, publication, and sharing of measurable data... and on the personal theological and philosophical views (or lack thereof) of the very scientists that "do" their science.

    Indeed, it even depends on the particular thought current and method to which a particular scientist subscribes. In the case of Biology, this is to say that there is more than one legitimate way to determine to what group an organism belongs, and each way may indeed provide a different result. Different combinations of morphological, behavioral, genetic, and other kinds of studies might make two different scientists place the same species in different genera, families, and even orders. (Classes and phyla are much more "stable").

    Even the empirical biological "species" - which is actually based on an Aristotelian philosophical construct - is not as easy to define (as opposed to describe) as it may sound. If the usual definition of "a group of genetically isolated organisms which, being such, can only reproduce successfully among themselves" is accepted, what about all-female, parthenogenic "species"? They do not reproduce among themselves (they do not mate but, rather, every individual is a clone of its mother). And what about the - rare but existing - fertile offspring arising from the genetic exchange of two different species, sometimes even belonging to different genera?

    Simply said, sometimes this it is not as easy as it looks.

    For more information on Systematics go to the Tree of Life Web Project at http://tolweb.org/tree/, and to http://www.ucmp.berkeley.edu/glossary/gloss1phylo.html.

The Terrestrial Chlorobionts

DIVISION BRYOPHYTA: NON-VASCULAR PLANTS

CLASSES BRYOPSIDA AND HEPATICOPSIDA: MOSSES AND LIVERWORTS

    This division (the plant equivalent of an animal "phylum") includes the chlorobionts which are ancestral to all others.

    Liverworts (Class Hepaticopsida) and mosses (Class Bryopsida) are two related groups, and are the most primitive of terrestrial plants save for some algae. It is in the warm and humid environments of the tropics where they are most varied and abundant. Rocks, tree trunks, and branches in cloud and montane dwarf forests of the Antilles are frequently covered in them. In fact, there are about 10000 species of mosses, making them the third most diverse group of terrestrial chlorobionts, after flowering plants and ferns.

    They can be mainly told apart by their rhizoids (what in them takes the approximate place of "roots"). Those of mosses are multicellular, while those of of liverworts are single-celled.

    Like the more advanced ferns, they have a two-stage life cycle: gametophytes for sexual reproduction, and spore-bearing sporophytes. However, they are distinguished from ferns in that they lack a vascular system to carry nutrients to the different parts of the plant. The organism absorbs what it needs to grow and reproduce directly through the cellular membranes of its tiny roots, and from there they pass directly to the rest of the plant through osmosis. This trait precludes mosses and liverworts from growing large and, indeed, none of them is more than a few centimeters in height.