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Variability in Saxifraga ferruginea Graham (Saxifragaceae) Randhawa , Ajit S.

Abstract

Saxifraga ferruginea Graham complex is widely distributed in the Pacific northwest and exhibits considerable variability. Different taxonomists have recognized the variability in different ways. Their decisions were based on morphological studies of herbarium specimens and plants in the field. The main objective of the present investigation was twofold: 1. to determine the extent of variability within the species complex. 2. to find out whether or not there is correlation between different characteristics to delimit sub-specific taxa. Fields of study from which information was derived were: cytology, morphology (living and herbarium specimens), embryology, anatomy, chromatography, and crossability involving different populations of the species range grown in the greenhouse at the University of British Columbia. Laboratory and field investigations were conducted during 1965-1968. Cytological observations and chromosome counts revealed 10-paired diploid as well as 19-paired polyploid (aneuploid) populations. Polyploids were in general more irregular in meiosis than the diploids. Embryological studies indicated an unusual behaviour of integumentary and nucellar layers, not reported earlier in the genus Saxifraga. This phenomenon was common to all populations examined. Morphological studies were carried out on herbarium specimens obtained for the entire range. Live plants representing different populations were examined for seed, leaf, flower and pollen characters. The characters used in the keys of previous taxonomists were carefully examined. The species was found to propagate sexually by seed, andvegetatively by plantlets developed in the inflorescence and by new crowns arising from the rhizome. Anatomy of the rhizome showed the presence of endodermis which is not present in the peduncle. Druses are common in leaves, sepals and ovary walls. In these and other anatomical respects the populations were alike. The chromatographic study gave a similar pattern of phenolic compounds for all the populations examined. S. ferruginea lacks 2, hydroxyphenyl acetic acid, a compound known to be present only in one genus, Astilbe, of Saxifragaceae. The polyploid populations were interfertile as were the diploids but with a reduced seed set as compared to intrapopulation crosses which served as controls. The reciprocal crosses between polyploid and diploid populations failed to set seed. The block to gene flow between polyploid and diploid populations suggests a genetic barrier favouring differentiation in time. The distribution of diploids and polyploids in S. ferruginea appears to be correlated to Pleistocene Glaciation in the Cordilleran Glacial Complex and plant migration in post-glacial times. This situation has been discussed. Although a tremendous morphological plasticity has been observed in the species complex, the only consistent difference among populations is the two chromosomal races. The other characteristics do not show any correlation with chromosome number so that the diploids and polyploids are morphologically indistinguishable. The conclusion is that although differentiation may occur in the future, establishment of subspecific categories is not warranted at the present time.

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