Updated Oct. 20, 2005 at 1:30am: Welcome to readers of Tangled Bank No. 39! If you don't know what Tangled Bank is, it's a biweekly collection of recent science-based writings and images from weblogs around the world, hosted by a different weblog for each edition – it's a great way to find out about other science weblogs!
Updated Oct. 17, 2005 at 8:05am: Welcome Boing Boing readers! If you're new to the site, you might like to check out a few other photos such as chocolate vine, 'Bright Lights' Swiss chard or the first BPotD, Melliodendron xylocarpum. Also, have a gander at the BPotD widget! – Daniel.
The idea and concept for this photograph of variability in autumn leaf colour of vine maple is thanks to Dan Otis, who assembled the collection for his own photo during the recent Maple Society Symposium field trip. Dan kindly allowed me to also take a picture, so I'm sharing it with you. Bear in mind, though, that if you like the image, please be sure to thank Dan in the comments, and not me – after all, all I had to do was show up and press a button after he did the work. This is the third in the series of three shots on Acer circinatum, previously featured here and here.
From a previous entry, Anthony asked “Why would being in the woods affect the color of the maple leaves?”, since I'd mentioned that the vine maples in the woods were yellow in autumn colour, while those in exposed sites were a brilliant orange-red. For an outstanding article on the topic, check out “Autumn Colours – Nature’s Canvas is a Silk Parasol” (PDF - 750K). Written by Dr. Rob Guy and Jodie Krakowski of UBC's Faculty of Forestry for UBC Botanical Garden's journal Davidsonia (I'm working on its new web site with open access to all recent articles), I'll quote the abstract to answer the question in brief:
“The variety and widespread nature of leaf colour change in autumn has led to investigation of the biochemical pathways and compounds responsible. The synthesis of bright red colouration initiated by longer nights prior to leaf abscission in deciduous species points to some adaptive value for this expensive ephemeral trait. It is hypothesized that during the breakdown of the unstable chlorophyll and the dismantling of the nutrient-rich photosynthetic apparatus, red anthocyanins provide a more biochemically parsimonious alternative to the elaborate xanthophyll system. This alternative enables leaves to screen out excess light energy and circumvent photooxidative damage to leaf cells, while allowing photosynthesis to persist at low rates in support of metabolic processes and phloem loading required for nutrient resorption from leaves.”
In other words, the formation of red pigments in the autumn provides protection, preventing the too-rapid breakdown of chlorophyll which could occur in exposed (read: excess light) areas. As you can clearly see in the leaf in the upper right, the bottom-right corner has the pattern of the leaf above. Where the leaf above shaded this leaf, no red pigments were produced. Where the leaf was exposed, bright red anthocyanins were formed. To take this to a broader perspective, vine maple trees in shaded forests and under low light conditions have little need to produce red pigments, as the breakdown of chlorophyll can occur at a modest pace. However, vine maples in exposed sites turn flame orange and red, so that the pigments produced will slow the rate of chlorophyll breakdown. The leaves in this photograph are from trees that are partially exposed, hence the attractive blend of colours.
No botany resource link today, since I'm answering one of Victoria's questions regarding plant taxonomy and names: Why is it that so many plants are in limbo as to their correct/finalized/accepted names?
I recently gave a lecture on the topic, and I had stated there were two broad reasons. I'm going to split one of those reasons into two, so I'll give three reasons here. Please know, though, that any one of these reasons can be combined with another one or all three can occur in a particular scenario.
The first reason is analogous to bookkeeping. Imagine a scenario where a name is published for a plant and it is later discovered that another taxonomist had already published the name describing a different plant (or, as has happened occasionally, the same taxonomist!). The most recent name would have to change since the older name (assuming everything is scientifically valid) would have priority. Or, imagine that someone names a plant that had already been named. The latter name is dropped as a synonym of the original version. Essentially, these rules try to enforce the notions that each species of plant has only one validly published name and that each name can only apply to one species of plant. As you might suspect, the modern days of rapid communication and information warehouses mean that names needing to change due to bookkeeping are now not a big proportion of the whole.
Disagreement about whether a subset of a species is distinct enough to be a subspecies or variety, and if so, which one of the two it should be is the second reason. I'll direct you to this page from the Brooklyn Botanic Garden on “How Plants Are Named” for a discussion on the differences between subspecies and varieties. Frankly, this is a reason that makes me roll my eyes, because it causes much consternation over a relatively trivial matter. Should it be Pallaea glabella subsp. simplex or Pallaea glabella var. simplex? From the BBG link, you'll note that some scientists have tried to define when each should be used. Other scientists argue that only one or the other is needed, and they then refuse to recognize the other when publishing floristic works or databases, so in the fern species above, some scientists would use subspecies and others would use variety. This reason for instability of plant names makes little sense in the face of the overwhelming loss of biodiversity.
The final reason is the biggie. You first of all need to know that the modern system for scientifically naming plants predates Darwin's and Wallace's Theory of Evolution. Plant nomenclature did not therefore have mechanisms to reflect evolutionary relationships, though plants were recognized as being part of identifiable natural groups (e.g., composites or legumes) and very similar plants shared the same genus. As the conceptual lynchpin of modern biology took hold, however, the same general system of plant nomenclature was mapped onto evolution, such that this general principle emerged: plant names and classification should reflect evolutionary relationships.
The utility of this principle is immense, simply because closely related plants share similar characteristics. Given a scientific name for an unknown plant, a taxonomist can make several predictions about its morphology. A biochemist can predict the compounds she might be able to extract or use the knowledge of plant relationships to target groups of plants in search of a particular chemical. A horticulturist can use methods from propagating related species to increase the chance of successful propagation, perhaps helping conserve an endangered species. I'll expand on this area when I answer Victoria's question about the importance of taxonomy, but it will suffice for now to say that the predictive value when nomenclature and classification are tied to evolution is supremely important.
The downside, however, of tying the two together is that our understanding of evolutionary relationships both continues to develop and will doubtfully ever be completed. As new techniques are developed (e.g., rapid analysis of nucleic acid sequences) or new evidence is found (e.g., fossils, new species), different hypotheses may be formed about evolutionary relationships. Given that plant names and classification should reflect evolutionary relationships, the name of a species, genus or family may change to reflect the new hypothesis. It so happens that the rapid accrual of information through modern molecular techniques is causing a significant clarification of plant relationships, therein also requiring significant changes to plant names recently. Will it ever settle down? Perhaps, but it is hard to predict what future techniques might be developed to determine relationships. I suspect, though, that the massive loss of biodiversity will sadly make things simpler for our descendants due to smaller datasets.