The Marsh Orchids in Hampshire and Dorset: Some Recent Research
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Proc. Hampsh. Field Club Archaeol. Soc. 47, 1991, 225-252 THE MARSH ORCHIDS IN HAMPSHIRE AND DORSET: SOME RECENT RESEARCH By MARTIN N JENKINSON ABSTRACT nomy in relation to morphology ie nomencla- tural classification on the basis of distinctive The recent history of the study of the tetraploid marsh orchids floral and vegetative characteristics of the vari- (Dactylorhiza majalis sspp.) presents a picture of controversy ous recognised members of the D. majalis group and confusion. The reasons for this are explored, with an (and indeed some which are not). In common account of recent developments. Some populations in Hamp- with several other workers, I have been ac- shire and Dorset are compared with others elsewhere in the tively involved in such research for several country, by means of multivariate analysis of morphometric years, and it may be that a helpful schematic data. Some potential solutions to the problems, and avenues resolution of the group is beginning to emerge, for further investigation are explored. The problems and as detailed knowledge of these orchids in- relevance of hybrids are discussed. creases: opinion however remains divided. It must be stressed that such research is continu- ing, and is likely to do so for many years. In the INTRODUCTION meantime, it may be helpful for me to outline my own research, to examine the results to The orchid group known collectively as the date (subject to the proviso that it is as yet Dactylorchids {Dactylorhiza Soo spp.) causes incomplete), and to attempt to offer some more problems of identification than any conclusions and avenues for future enquiry. other, both to amateur botanist and expert orchidologist alike. It consists of two main subgroups, the spotted orchids and the marsh orchids. Whilst the spotted orchids and the THE PROBLEMS members of the Early Marsh Orchid group, the diploid marsh orchids (D. incamata (L.) Soo The degree of taxonomic confusion in this sspp.), are fairly readily distinguished, few group is caused by two main factors peculiarly botanists (including many orchid specialists) characteristic of the tetraploid marsh orchids, are able confidently and accurately to identify to some extent compounded by the nature of all subspecies and varieties of the tetraploid some past research and attitudes of some marsh orchid group (D. majalis (Reichenbach) workers. P F Hunt & Summerhayes). Even the few The main difficulty is in assessing the cur- recognised experts disagree with alarming rent taxonomic status of the marsh orchids, consistency. It is this subgroup therefore when it is apparent from all the available which forms the principal subject matter of evidence that the group is in an extremely this paper. fluid state of active evolution. This process is I shall summarise the difficulties caused by most apparent in the tetraploid group. the group, attempt to account for them, and It has been suggested that D. majalis may be outline some of the recent research which has a comparatively young species in the process attempted to resolve them. They are not yet of stabilisation; on the other hand, it has also fully resolved, by any means, and research been proposed that it may be an old species continues into various problematical aspects being progressively altered by the continuous of the biology of this difficult group. influence of hybrids (Summerhayes 1951, et My own particular area of research is taxo- al). My own view, to some extent supported by 226 HAMPSHIRE FIELD CLUB AND ARCHAEOLOGICAL SOCIETY hybrid evidence that I shall outline later in this ecological change, and therefore of outliving paper, is that it is a very young species indeed. the less adaptable parent plants in sites under- Unfortunately, what little evidence is available going progressive change, and also of perpe- is capable of use in a cyclic argument that can tuating themselves with consistent inbreeding. support either point of view: as yet there is no Attempts to resolve the problems posed by conclusive proof either way, and indeed may apparent evolution and hybridisation amongst never be. Whatever the correct view may be, I Dactylorhiza, and to produce an acceptable tax- have noticed that over a period of years, signi- onomic organisation of the group, have to an ficant changes can occur in the morphology of extent suffered from the limitations of both the plants in some populations. Whilst in most research itself and of the workers involved in populations such changes are slight (and per- the research. Many workers have tended to haps attributable to ecological change), in concentrate their attention on a comparatively some they are quite marked - to the extent small number of distinguishing characteristics that I have altered my opinion on identifica- in order to determine the taxonomic status of tion of some plants in the same population particular groups of Daclylorkiza. For example, over a period of twenty years or so. The great emphasis has always been placed on reasons for such changes are difficult to deter- differences in labellum shape and markings: mine, but those populations which show the examination of Figure 3 in this paper will show most marked changes are geographically at once how unreliable it is to place too much isolated from others, and also contain more emphasis on those features alone. The extent than one species of Dactylorchid: the progress- of labellum variation within subspecies of D. ive influence of hybrids is therefore a legiti- majalis is such that individual plants within a mate assumption. It is hybridisation, of population of one subspecies will often show course, which is the second major factor con- the characteristic features of another subspe- tributing to the problems posed by the marsh cies. Other characters such as number, length orchids. and breadth of leaves, type and degree of leaf The exceptional propensity of Dactylorkiza markings, level of anthocyanin staining of spp. to hybridise with each other is well known stems and floral bracts, and colour of flowers amongst orchid enthusiasts: I have even heard have all assumed considerable importance in them described by one as 'an incestuous little the determination of taxa: examination of the lot'! The welter of forms to be found in the majority of floras and flower keys, and even average mixed colony has to be seen to be many specialist papers, will show that they believed. Identification of the individual plants tend to concentrate on a small number of concerned can at best be putative, and at worst features such as these, and ascribe 'diagnostic' is sometimes impossible. Whereas many plant significance to alleged differences between hybrids are infertile, that is not true of Dactylor- taxa in these features. Recent research how- kiza hybrids: most of the Fl hybrids produced ever (Bateman & Denholm 1983) has shown from initial crossings of two species are them- that the diagnostic status of some of these selves fertile, and hence capable of further much-used character-states is not supported hybridisation, both with each other, and with by the morphometric evidence. I shall also the original parent plants (introgression). show that my own studies have revealed What is more, it is my belief, based on what I certain potentially diagnostic features that have observed in certain populations in the have never before been considered, and have New Forest (see p 247 below), that even these also considerably weakened certain characters further hybrids retain a high degree of fertility. as potentially diagnostic. Dactylorkiza groups The marsh orchids hybridise particularly fre- have thus, it would appear, been subdivided quently with the spotted orchids: the resultant into species, subspecies and varieties on the forms are usually robust vigorous plants, ap- basis of a small number of rather minor differ- parently capable of considerable resistance to ences: the examination of a much wider range JENK1NSON: THE MARSH ORCHIDS IX HAMPSHIRE AND DORSET: SOME RECENT RESEARCH 227 of floral and vegetative characteristics, and of taxa. Furthermore, widening the scope of such the range of variation apparent in a large analysis, to sample populations from as wide number of different marsh orchid populations an area as possible of not only the British Isles, from a wide area, presents a rather different but also of Continental Europe, would vastly picture. enhance the validity of taxonomic decisions, Thus the parochial nature of some research and perhaps ultimately arrive at a more satis- work must have a considerably more limited factory schematic resolution of this difficult application than that claimed for it by the group of orchids. workers concerned. What one worker has I make no such ambitious pretentions for described as 'taxonomic chauvinism' is a fea- this paper, however: that is for the future. I ture of much past research: the status acquired shall simply compare some marsh orchid po- in botanical circles by the claiming of a new, pulations in Hampshire, Dorset, Oxfordshire, perhaps rare taxon for the local county flora, or Gwyncdd, Dyfed and Yorkshire, in order to the naming of a hitherto undiscovered taxon, give the reader some idea of the problems we has tended to militate against taking the wider face, and perhaps give some useful clues as to over-view. More pragmatically, the expen- the likely eventual resolution of those diture of time, money and effort that is problems. required in order to make adequate compari- sons of a large number of samples from a wide geographical range must inhibit much valua- THE TETRAPLOID MARSH ORCHIDS: ble work. In Europe, for example, there are RECENT HISTORY wide differences in the assessment and distinc- tion of taxa from those prevailing in the British Until comparatively recently, it was widely Isles: the two spotted orchids, D.fuchsii and D. accepted that there were five full species of maculala, regarded as separate species in marsh orchid present in the British Isles, as Britain, arc treated on the Continent as con- follows: specific (Sundermann 1980, Buttler 1986) - 1.