Another little study done. Just over a year ago I summarised some of the work I was doing looking at orchid leaves under the microscope to see if they helped identification. I added a lot more data in 2018, especially on helleborines (Epipactis) and over the last few days I have revised my summary in a Powerpoint presentation. If anyone is interested then it can be downloaded by following this link to my dropbox account Orchid Leaf Edges TS
In all I examined 36 orchid species, and ignoring the Schedule 8 plants and those without leaves, there are another 5 on which I would like to collect data. All were examined at x100 from small slivers of often damaged leaves using a home microscope. In the field it is possible to get up to around x40.
Most have regular, toothed, leaf edges, with peaks and troughs, and I used several terms to describe those tooth patterns, to try to capture subtle differences. I measured the width of the teeth, and the peak height over the trough. Where teeth were angled I measured the average slant. Some though, such as the butterfly orchids (Platanthera) and the bee orchids (Ophrys), had entire edges (i.e. not indented). Some had spotted leaves, some had purple tinged edge cells. Some had stomata on the upper leaf surface, others did not. Two other measures were the shape and appearance of the leaf tip, and the number of leaf veins. All were faithfully recorded by photographs.
A few - helleborines - did not have regularly patterned edges, but rather, unequally sized papillae, together with areas of only small obvious edge cells, or indeed gaps.
There are definite differences between most species of marsh orchids (dactylorhiza), although common spotted and heath spotted were similar. The 3 fragrant orchids showed subtle differences, for example chalk fragrant had more crowded teeth then the other two, and upper leaf stomata were more likely. The helleborines also had some differences but maybe not enough to safely attribute a species name to a particular plant. Nevertheless leaf edge characteristics might be useful in the mix of plant morphological characteristics in identification.