Methodus Plantarum Nova [1682]

Abstract

parents, distribution and habitat in the British Isles and to some extent in Europe, data on fertility/sterility, chromosome numbers and experimental work. I would question the sequence of the parents in the names (e.g. Salix pentandra× alba), often not in alphabetical order and differing from the index (S. alba× pentandra). The extent of the texts varies considerably depending on the available information and importance of the hybrid, but also on the personal interest of the authors and editors. A useful list of illustrations is given for each hybrid and nice colour photographs of several hybrids are included. Each hybrid description includes a table of hectad totals separately with each parent, and for all but the rarest spontaneous hybrids a hectad map is given showing the distributions of the hybrid and its parents. The maps are otherwise similar to those in the New Atlas of the British and Irish Flora but lacking age and status information. Unfortunately, status information is not given in the tables, either, and the reader cannot easily see the essential role of introduced plants in the hybrids, so the New Atlas of the British and Irish Flora must be consulted. Hybrids arise where the parents meet. So it is not astonishing that usually both (or all three) parent species are present in the area where a hybrid is noted – this is neatly seen in the maps. If one or both of the parents are absent from a hectad, it is usually matter of under-recording or disappearance. Hybrids are commonly sterile or with low capability to spread generatively, but they have often good capability to vegetative spreading to large vigorous colonies, which can establish for decades or centuries. Good examples are Circaea × intermedia, much more widespread than one of the parents (C. alpina) at present, Nuphar × spenneriana, rare but widespread whereas one parent (N. pumila) is restricted to northern Scotland, and Potamogeton × bottnicus with one of parents is completely missing from the British Isles. In case of Crataegus×media, its abundance in the north, outside the area of C. laevigata, tells of frequent plantings and escaping of the hybrid there. Most spontaneous hybrids between native plants are rare and exceptional, because plants have different genetic and biological mechanisms to prevent hybridising. However, some hybrids between native taxa are widespread in the common area of the parents, as, among others, in many hybrids in Salix and in Geum rivale × urbanum, Nasturtium microphyllum × officinale, Hypericum maculatum subsp. obtusiusculum × H. perforatum, Mentha arvensis × aquatica, Stachys sylvatica × palustris, Senecio jacobaea× aquaticus, Festuca pratensis × Lolium perenne andGlyceria fluitans × notata. Often disturbance of habitats breaks ecological isolation and makes meeting of parents more probable. In many widespread hybrids between native and alien species, such as Bromus hordeaceus × lepidus, Hyacinthoides non-scripta ×H. hispanica and Senecio jacobaea × S. cineraria, originally geographically isolated species have become together resulting many of the most widespread and best-established hybrids. Interestingly, hybrids between American Epilobiums and native taxa are in Finland clearly less often recorded, so may be under-recorded? Numerous hybrids have arisen accidentally or by purpose in gardens. Many of them are widespread in cultivation, but also freely escaped especially with garden refuse. Some are more common and widespread than the native parents, if present. Their number and role in flora, vegetation and landscapes can be prominent. Examples include Symphytum× uplandicum, Saxifraga× urbium, Polygonatum × hybridum and many hybrids in Spiraea, Rosa, Ulmus and Narcissus. From the clear and formally exact descriptions, exact numbers in the tables and attractive maps the reader can get an impression that hybrids are not so difficult and wonder why they are neglected in Floras. But the situation is not always clear-cut. The text frankly gives many cases where difficulties exist in delimitation of the hybrids, especially between morphologically similar parents and when highly fertile. Especially critical are genera like Crataegus, Betula, Salix, Euphrasia and Dactylorhiza. Probably some of the hybrid definitions will not hold in the future. In many hybrid descriptions the editors have to mention that the data is insufficient and the maps do not give a proper picture of the probable frequency and the area. So in hybrids, there is still much to do also for field botanists. Hybridisation has great importance not only in developing cultivated plants but also as a continuous process going on in the native flora and between native and introduced species.Hybrid Flora of the British Isles with its 499 pages, sized 25 × 32 cm, is a unique compilation of the information on hybrids and this process, and it will be a standard book for botanists not only in the British Isles but also elsewhere in Europe.