A BIOSYSTEMATIC STUDY OF SOME GLYCERIA SPECIES IN BRITAIN* 



1 . Taxonomy 



/ 



By Martin Borrill 



Welsh Plant Breeding Station, Aherystwyth'f 



Introduction 



The genus Glyceria, a critical taxonomic group, has been the subject of several recent 

 papers. The wider aspects of its classification and cytology have been dealt with by 

 Church (1949). The taxonomy of the British species has been studied by Hubbard 

 (1942, 1954), Lambert (1949) and Jungblut (1953'), whilst the cytology has been investigated 

 by Maude (1939) and Fitzpatrick (1946). The diploid species G. declinata has formed 

 the subject of papers by Walters (1948) and Stormer (1951). 



It is generally agreed that in Britain the following three species of section Glyceria^ 

 and one hybrid occur : 



During the course of biosystematic studies to be described in subsequent papers, 

 it was found that a proportion of the specimens could not be classified with complete 

 confidence. The taxonomy of the group was therefore investigated in an attempt to resolve 

 this difficulty, and the results are given here. 



The homogeneity of the species 



The variability of the species suggested the presence of intraspecific chromosomal 

 races. Such races usually have detectable morphological differences (Muntzing 1936), 

 and in order to study phenotypic variation from this point of view numerous herbarium 

 specimens were examined, measurements being made of lemma length, anther length, 

 and pollen diameter. 



The specimens were selected in order to include plants from diverse geographical 

 localities and types of habitat. In each species, the frequency distribution of these taxono- 

 mic characters approximated to a normal curve, as illustrated for anther length in G. fluitans 

 in Fig. 1 and for pollen diameter in all three species in Fig. 2; they therefore belonged 

 to a single population in the statistical sense, showing that widespread intra-specific 

 chromosomal races are absent. 



Critical taxonomy 

 General Remarks 



Floristic characters show wide and overlapping ranges of variation as can be seen 

 in Table 1. Vegetatively, and in growth habit, the species intergrade so extensively 



• Part of a thesis for the degree of Ph.D. of the University of London. 



t The experimental work for this investigation was carried out in the Botany Department of the University College of Leicester. 

 J;The sectional name Glyceria replaces the name Euglyceria proposed by Grisebach in 1853, in accordance with the new rule 

 that : " the subgenus or section containing the type species of a generic name must bear that name unaltered." 



1. G. fluitans (L.) R. Br. 2n 



2. G. plicata Fr. , 2n 



3. G. declinata Breb. 2n 



4. G. X pedicellata Towns. (G. fluitans X G. plicata) 2n 



40 

 40 

 20 

 40 



291 



