Ramicauls, pleurothallids, sympodial orchids
I've spent all day (literally) trying to determine, exactly, what a ramicaul is. I love pleurothallids, with Masdevallia and Dracula being my favorite genera (though the maxillariinae get an honorable mention, as do podochilaeae), so in reading about just about anything involving pleurothallidinae, you have all of these mentions of ramicauls. As far as I could ever figure, the general habit of pleurothallids was more or less like any other sympodial orchid; you have a rhizomatous structure that forms as a result of generalized meristem growth extending upward to becoming a new leaf structure and downward to form roots, and as both mature the horizontal stem hardens and lengthens. I just think of Cattleyas as the quintessential sympodial orchid; new roots only grow from areas where there are also new leaves, and the overall "success" of the new leaf (as judged by whether or not it blooms) seems to be more or less entirely dependent on the "success" of the new roots to attach the plant more firmly to its base, and also to absorb sufficient water and nutrients. The general structure of a Cattleya leaf is you have a short, vertical stem, then a pseudobulb, then the actual leaf; if the plant is happy and everything is provided for it, then a flower spike will additionally grow from the base of the leaf, at the top of the pseudobulb.
Where pleurothallids differ, primarily, is that they do not form pseudobulbs. Being primarily cloud forest plants, they have no need to accommodate for drought periods and can just "assume" constant moisture. Therefore from the rhizomatous horizontal stem, new leaves form, just like with Cattleyas and other sympodial orchids, from the ends. However, perhaps a little more obviously than the Cattleyas, the roots actually appear after some time from the vertical leaf stem; the undifferentiated area between rhizome and leaf, which is the ramicaul. Each leaf-ramicaul-root unit is, in many ways, a fully realized individual plant, which is connected to each other leaf-ramicaul-root unit via the rhizome in order to share water, nutrients, and security. And, over time, the rhizomatous part can dry up and the growing end of the branch goes off on its own as a new "clone" of the original plant.
Nevertheless, the ramicaul seems to be the "business" part of a pleurothallid of any stripe. Not only does the leaf grow from one end and the roots from the other, but the flower spikes emerge from one end or the other of the ramicaul as well. With most members of Stelis, Pleurothallis, and others, the flowers come from the top of the ramicaul, seeming to emerge from the base of the leaf. With Masdevallias, Draculas, and others, the flowers emerge on comparatively long spikes that come from the base of the ramicaul and hang pendulously from the plant.
My question is this: on Cattleyas, to use them once again as an example, is the stem between the pseudobulb and the rhizome technically a ramicaul as well? At least on a Cattleya the roots grow more obviously straight from the very base of the growth, out of what becomes the rhizome. On the Dracula lotax I have, the roots grow out of several areas in the ramicaul and sometimes wrap around the rhizome, but don't appear to grow properly from it. Or is the stem on a Cattleya leaf just a stem because it does not have as much breadth of function as a pleurothallid ramicaul?
