| BEN |
| BOTANICAL ELECTRONIC NEWS |
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| ISSN 1188-603X |
| No. 257 September 21, 2000 | aceska@freenet.victoria.tc.ca | Victoria, B.C. |
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A very large rock has been tossed into the placid pool of classical plant taxonomy. This article will describe the implications of the resulting wave on the palaeobotanical community at large.
On August 6, 2000, I travelled with Adolf and Oluna Ceska from Victoria to Portland, Oregon, to attend 'Botany 2000, New Frontiers in Botany', for the annual meetings of the American Bryological and Lichenological Society, American Fern Society, American Society of Plant Taxonomists, International Association of Plant Taxonomy, and the Botanical Society of America. As a member of the Palaeontological Section of the latter group, I was keen to attend this gathering of approximately 900 attendees, for 4 days of talks, poster sessions, and informal meetings with current palaeobotanists. I divided my time mainly among the systematic and palaeobotanical sessions, which I briefly report here (for more info, abstracts, etc. see the website: http://www.botany2000.org/).
The 'rock in the pool' was actually launched last summer (1999) at the 16th International Congress held at the Missouri Botanical Gardens in St. Louis. Dubbed 'Deep Green' and with a grant of $285,000 USD, 200 scientists from 12 countries confronted classical Linnaean taxonomy (where all organisms are divided into the standard taxa we all learned in school - kingdom, phylum, class, order, family, genus, species, mainly on the basis of morphology), to replace it with phylogenies based on new data, involving sequencing of DNA and other strategic biomolecules, statistical analyses, and phylogenies based on cladistics (construction of hypothetical 'phylogenetic trees' or cladograms). See their website at: http://ucjeps.herb.berkeley.edu/bryolab/greenplantpage.html
That Botany 2000 was hit by a wave of tsunami proportions from the 'Deep Green' rock is evidenced by the excitement observed in the otherwise staid halls of Academe. Using sophisticated lab hardware, complex probability theory, and ornate computer programming, otherwise impossible-to-handle massive data sets are crunched down to produce the modern analog of the old 'family trees'. Called cladograms, these branching diagrams are read left to right, to show increasing diversity and presumed evolutionary pathways for the taxa under consideration. Reaction to the new methodology has been swift, from "It's moronic!" (William Berger, Curator of Botany for the Field Museum in Chicago), to "I think it's the greatest thing since sliced bread." (Michael Donoghue, Director of Herbarium, Harvard University). Some random notes from these sessions follow.
Cladistic phylogeny is attempting to integrate data from classical morphology, biochemistry, and palaeobotanical sources. An interesting first, as an example: a group of researchers have been able to extract 'geolipids', in this case terpenoids from Miocene (Clarkia Flora of Idaho) fossil leaf and cone material from five different fossil conifers (Metasequoia, Taxodium, Cunninghamia, Glyptostrobus, and Calocedrus), compared them to their modern counterparts, and found significant differences which can distinguish the genera from each other, as well as demonstrate degrees of interrelationship. If the new system of cladistic phylogeny becomes widely adopted, the old Rules of Binomial Nomenclature will be replaced by the PhyloCode, with a new set of rules based on cladistics (see http://www.ohiou.edu/phylocode/).
An interesting and well organized treatment of this information can be found on the website: http://www.ucmp.berkeley.edu/exhibit/phylogeny.html and is highly recommended to the reader who wishes to learn more about this new and rapidly emerging branch of bioscience.
The many linkages between terrestrial higher plants and geology have a long and colorful history. The first real scientific contributions were made during the first part of the 19th century. Primacy goes to Alexander von Humboldt who described the effects of altitude on plant life during his tour of Andes (Humboldt, 1805). Goran Wahlenberg (1814), in his flora of the Carpathians, noted effects of geology on plant distribution. But the most notable contribution was made by Franz Unger (1836). What follows on Unger is an excerpt from a new book in press by Art Kruckeberg, Plant and Geology - A Global View (Kruckeberg, 2001).
It is to Franz Unger (1836) that we turn for a full-blown conceptualization of the geology/plant connection. Unger (1800-1870) had a long and productive career in plant science; he made influential contribution to the growing science of botany in areas of cell biology, anatomy and morphology, palaeobotany, and plant pathology. But his earliest adventures with plant life were ecological. In that great 19th century encyclopaedic work, The Natural History of Plants, Anton Kerner von Marilaun gives us a vivid picture of the patterning of vegetation by substrate that set Unger to develop his chemical concept of plant distribution. I quote at length from this picturesque account, from the English version, volume 2 (Kerner and Oliver 1902, pp. 495-496):
"The little town of Kitzbuhel, in the Northeast Tyrol, has a very remarkable position. On the north rises the Wild or Vorder Kaiser, a limestone chain of mountains with steep, pale, furrowed sides, and on the south the Rettenstein group, a chain of dark slate mountains whose slopes are clothed far up with a green covering. The contrast presented by the landscape in its main features is also to be seen in the vegetation of these two mountain chains. On the limestone may be seen patches of turf composed of low stiff Sedges, Saxifrages whose formal rosettes and cushions overgrow the ledges and steps of the rugged limestone, the yellow-flowered Rhododendron, and white-flowered Cinquefoil adorning the gullies, dark groups of Mountain Pines bordered with bushes of Alpine Rose; and opposed to these on the slate mountains are carpets of thick turf composed of the Mat-grasses sprinkled with Bell-flowers, Arnica montana and other Composites, groups of Alpine Alder and bushes of the rust-coloured Alpine Rose - these are the contrasts in the plant--covering which would strike even a cursory observer, and would lead a naturalist to ask what could have been the cause. No wonder that the enthusiastic botanist, Franz Unger, was fascinated by this remarkable phenomenon in the vegetable world. In his thirtieth year, furnished with a comprehensive scientific training, he came as a doctor to Kitzbuhel, and with youthful ardour he used every hour of leisure from his professional duties in the investigation of the geological, climatic and botanical conditions of his new locality, devoting his fullest attention to the relations between the plants and the rocks forming their substratum. The result of his study was his work, published in 1836, On the Influence of Soil on the Distribution of Plants as shown in the Vegetation of the Northeast Tyrol, which marked an epoch in questions of this sort. The terminology introduced in the book found rapid entrance into the botanical works of the time. Unger divided the plants of the district accordingly to their occurrence on one or other of the substratums -- in which lime and silica respectively predominated -- into (1) those which grow and flourish on limestone only; (2) those which prefer limestone, but which will grow on other soils; (3) those which grow and flourish on silica only; and (4) those which, whilst preferring silica, will grow on other soils."
The essence of Unger's view -- that mineral content of rocks and soils is the major edaphic influence on substrate-specific plant distribution -- has been substantiated over and over again in modern times. Unger's attempt to quantify the mineral nature of the substrate differences, was to carry out analyses of ashed plant parts. As Kerner pointed out, this approach failed, but the key concept of mineral difference s remains viable. Kerner became a disciple of Unger's ecological ideas and carried out transplant and pot test studies on species from limestone and siliceous rock habitats. He explained the plant responses as follows (Kerner and 0liver 1903, p. 498):
"The difference in the vegetation on the closely adjoining limestone and slate mountains ... can be accounted for most satisfactorily in the following way. Plant species which demand or prefer a siliceous soil are absent from limestone mountains wherever their roots would be exposed to more free lime than is beneficial; if present they would be weakened, and thus vanquished in the struggle with their fellows, to whom the larger quantity of lime is harmless, and they would eventually perish. These plants flourish luxuriantly, however, on slate mountains because there the soil does not contain an injurious amount of lime. The absence of species, demanding or preferring lime, from slate mountains can be explained in the same way."
It is curious to note that Unger's earliest work, cited above, is not considered by botanical historians as his major contribution. Besides being the co-author (with Endlicher) of a popular botany text, Unger made major contributions in palaeobotany and historical plant geography, as well as in plant anatomy, plant pathology and cell theory. His stand in debate with Schleiden on cell division has been upheld and his ideas on evolution, though attacked by the clergy of the day, presaged some of Darwin's ideas. Interestingly, Unger was a teacher of Gregor Mendel in Vienna. "Unger's involvement in the working out of the cell theory and its application to the fertilization process may well have played a crucial role in equipping Mendel for the cytological interpretation of his breeding experiments" (Dictionary of Scientific Biography 1978, p. 542).
Unger appears to have pioneered the "Chemical Soil Theory" (Braun-Blanquet, 1932) which asserts that the inorganic constituents of the parent rock and derived soil strongly influence the response of plants. It was not unexpected, then, that a contrasting "Physical Soil Theory" would emerge. It belittled the chemical effects and emphasized the importance of physical properties (texture, particle size, porosity. etc.) in determining the nature of plant responses. The first acclaimed proponent of the Physical Soil Theory was Jules Thurmann (1849). In his Essai de Phytostatique Thurmann emphasized both textural differences (psammitic or coarse textured soils versus pelitic or fine-grained clayey soils) as well as the capacity of weathering of parent rocks (eugeogenous rocks, high in silica that weather readily versus dysgeogenous rocks like Iimestone and chert that weather slowly). And so, in the mid-nineteenth century a lively debate was joined; the two "hostile camps", so described by Braun-Blanquet (1932), kept the contrasting theories in the air for the remainder of the 19th century. The debate continued on to the time in the early 20th century when soil science had acquired its major breakthrough, discovery of the colloidal soil fraction and its role in cation exchange in soils. From this salient discovery (in the 1920s) and other influences, adherence to either the chemical or physical theories dissipated. It was then realized that both sets of factors are complexly interactive to yield a particular plant-soil system.
References
For those of you who visit the BEN archive on the Web (http://www.ou.edu/cas/botany-micro/ben/), you may already be familiar with a new full text search engine, implemented to search old issues from volume 115 (October 15, 1995) to the present. This was implemented at the beginning of August. A convenient input box is provided on the home page for a default search of the site, which searches for all terms and is case insensitive. If you like options, you will prefer visiting the search page, which allows searches for an "exact phrase", "all" search terms (which is the default) or "any" of the terms given in a phrase. There is also an option for case-sensitive searches or case-insensitive searches (the default) which may be useful for finding specific terms. This is a "no-frills" search engine, so the linked BEN issues that are returned may need to be searched by issue using the browser search key (in the edit menu of your browser), which will jump from one term to the next in the document. The issues are arranged by number of "hits" for the term and then by issue number.
Tables of Contents (listed on separate pages by year) and the alphabetical subject index are still available on the site -- they are just augmented by the search engine. I wrote the search engine because both tables of contents and indices are horribly inefficient at finding data that the writer, editor and/or indexer did not recognize were useful at the time.
On another happy note, I was able to meet Adolf and Oluna Ceska for the first time, in person, during the Botany 2000 meetings at Portland and share dinner. As you may be aware, I started archiving BEN with the same enthusiasm and foresight that Adolf had, without even having met him beforehand. Our meeting has been duly documented with digital images on the Web. The images are at http://www.ou.edu/cas/botany-micro/ben/ceska.shtml