Difficulties arise in identifying groups of plants for various reasons: some groups are just too large! There are a lot of umbellifers (the parsley family), not very similar to each other but it is hard to remember them all. Other groups consist of many closely related, and very similar, species whose identification requires very close examination (for example, the Lady’s Mantles (Alchemilla), or the Eyebrights (Euphrasia)). Others groups are difficult for other reasons and many may justifiably throw their hands in the air, or at least shrug their shoulders! Consider small creeping plants with smooth eaves in opposite pairs that grow in damp or watery areas, especially in mud, many of which root along their stems.* These are too inconspicuous for many to bother with, but come from a wide range of unrelated families. Not only do these look superficially similar, but some vary quite considerably accordingly to where they grow – they are `polymorphic’ – varying with the depth and speed of flow of the water and the substrate (mud, sand or rocks) and often looking very different in different environments. Worse than this, some rarely flower, so that no flowers or fruits are available and we have only stems and leaves for identification purposes.
So why bother with such difficult and inconspicuous groups? Well, that is what botanists do! And, as usual, the more closely we look, the more interest there is, and from such observations occasionally great discoveries are made. So with one such sample (above), gathered from a burn in Olav’s Wood in Orkney, I visited the University of Manchester Herbarium – a magnificent and historical collection, with approximately one million specimens many dating back to the mid 19th century. This is valuable not only as all good herbaria are – an important resource for plant sciences – but also because many of the specimens are from sites in the UK (and elsewhere) now lost, and moreover ancient specimens open up the possibility that we can examine how plants may have changed, even over 100-150 years. The difficulties of identification are shown in the herbarium specimens. Some of the Water starworts (Callitriche) have three labels attached over the decades with different names (partly because species boundaries have become clearer) and few have any flowers or fruit. Stace [New Flora of the British Isles, Clive Stace. C.U.P. 19191] says of the Water starworts “leaf-shape is notoriously variable and misleading” and “difficult to identify certainly without a strong lens or microscope”. I’ll only be satisfied if I can get my specimens to flower and fruit, but don’t wait around!
* Amongst such plants are the Blinks (Montia), Water starworts (Callitriche), Waterworts (Elatine), Bog stitchwort (Stellaria uliginosa), Water purslane (Lythrum portula), Pigmyweeds (aquatic Crassula species), New Zealand Willowherb (Epilobium brunnescens) and Bog pimpernel (Anagallis tenella). A useful article on these plants can be found in the BSBI (Botanical Society of the British Isles) News No. 106, September 2007: Maddening Mimics: a belated reply.