Re-evaluating species boundaries among members of the Posidonia ostenfeldii species complex (Posidoniaceae) - morphological and genetic variation

A taxonomic re-examination of the Posidonia ostenfeldii complex was underta ken based on field collections in Western Australia. Broad and narrow leave s of seagrass of the Posidonia complex from Success Bank were compared to P . kirkmanii, P. coriacea, P. robertsoniae and P. denhartogii, identified ba sed on their distribution as described by Kuo and Cambridge (1984). The bro ad and narrow leaf varieties of Posidonia on Success Bank were unable to be identified to species due to the overlap of character ranges between group s. Multivariate analysis of 10 vegetative characters examined indicated a c ontinuous variation of character traits within the complex, suggesting the existence of a morphological continuum. Genetic variation was also examined using starch gel electrophoresis, restricted to Success Bank and Marmion p opulations. No allozyme polymorphism was observed among all the samples tes ted across both populations and varying leaf widths. All loci were monomorp hic and homozygous. This study implies that the key of vegetative morpholog ical characters, upon which five species of the P. ostenfeldii complex was erected, was not effective for the identification to species of multiple sa mples from any one location. Presently there is no justification for suppor ting Posidonia coriacea and Posidonia robertsoniae as separate species and it is further recommended that the whole group be reanalysed. (C)2000 Elsev ier Science B.V. All rights reserved.