MINT NOTES 



111 



terminal capitulum only, or commonly with up to two pairs of underlying, axillary verticils, 

 occasionally with as many as eight pairs which are contiguous at least at the apex thus 

 forming an obtuse spike (such a form is the example recorded by Miss Muirhead from 

 R. Eden, Cumberland, v.c. 70, in 1952, Watsonia, 2, 204, which I tentatively, and erro- 

 neously, named as M. X palustris Sole). Calyx glandular, ribbed, always tubular, shortly 

 ciliate to densely shaggy with usually ascending hairs, probably never quite glabrous or 

 even essentially so, the teeth J- J the length of the tube, occasionally rather longer. Pedicels 

 shortly to densely hairy with white or whitish, usually retrorse hairs, apparently never 

 glabrous. Peduncles of axillary verticils usually short, sometimes long and very notice- 

 able. Corolla 4-fid, sometimes deeply so, varying somewhat in size (depending perhaps 

 on sexuality), usually with a few scattered hairs externally and sometimes with a ring 

 of hairs in the throat. Stamens exserted or included, sometimes perhaps absent. (See 

 Schultz (1896, 433-434) for an interesting correlation of stamen development with the 

 size of the leaves and capitula). Scent minty, but rather dull and not sweet, nor pungent 

 as in M. spicata and M. piperita L. Very rarely examples are found with the scent 

 characteristic of M. citrata Ehrh. and it is possible that these may be hybrids although 

 they show no morphological indications of this. Those who wish for an anatomical account 

 should consult A. & E. G. Camus (1911). 



Typical M. aquatica L. is, in my opinion, only a form that, by a combination of 

 certain characters set out in the foregoing paragraph, can be selected out of the innumerable 

 forms that occur. But the different combinations of characters are so endless, and the 

 variation thereby so wide, and yet so gradual - indeed it is only seldom that one can exactly 

 match examples from different localities - that I believe M. aquatica L. to be a polymorphic 

 species whose division into the grades varietas and forma is taxonomically unsound. It is 

 perhaps unfortunate that a great many different forms have received names from eminent 

 speciaUsts of the past. 



The causes of the great polymorphism are not very clear. Cytological investigation 

 indicates that 2n^96 in most plants - if not all. Reproduction is largely vegetative, by 

 runners, and no doubt many mutants become perpetuated in this way as clones. Seed 

 is produced to a certain extent. No doubt also seasonal, edaphic and other environmental 

 factors play their part in influencing the final characters of any given form, and it is 

 clear that some of the named forms owe their status to such causes only. That the 

 degree of hairiness of the stem and leaves is controlled, at any rate in part, genetically, is 

 suggested by occasional occurrences of subglabrous and very hirsute forms sharing a 

 habitat. 



Strail, Braun, Briquet and Topitz are among those who have divided the water mints 

 into many named forms, using species, varietas and forma as grades for the purpose. Indeed 

 Topitz (1913, 168-179) contrived to recognise no less than 40. Leaf characters, degree 

 of hairiness, size of the capitula, presence of axillary verticils, and degree of branching 

 are among the chief criteria used for differentiation. Strail regarded the exsertion or 

 inclusion of the stamens as an important character, but this is probably a matter of sex- 

 function. In my view, all the varieties listed by these and other authors (except var, 

 nemorosa Fr.) are merely examples selected from the great variational range. Many are 

 closely allied, and identification according to any of these four authors, or all, becomes a 

 task of distracting difficulty. This is particularly so in view of intermediates, because, no 

 matter how many named forms there are, intermediates will always be found in a species 

 as polymorphic as this, and with so many names to choose from the correct placing of 

 any given intermediate often becomes taxonomically impracticable. 



This paper, in view of the complexity of the problem, should be regarded as a 

 prelijminary attempt to simplify the British water mints as a whole - to restore a semblance 



