Disjunct, highly divergent genetic lineages within two rare<i>Eremophila</i>(Scrophulariaceae: Myoporeae) species in a biodiversity hotspot: implications for taxonomy and conservation

Abstract

Effective conservation management should target appropriate conservation units, but evolutionarily and genetically divergent lineages within nominal taxa are often unrecognized. The south-western Australian biodiversity hotspot may harbour many cryptic taxa, as it contains many plant species with naturally fragmented population distributions. Using microsatellite markers, we tested the hypothesis that disjunct population groups in the rare species Eremophila microtheca and E. rostrata (Scrophulariaceae: Myoporeae) are highly genetically divergent and represent separate evolutionarily significant units (ESUs). Chromosome counts indicated that all individuals assessed were diploid (2n = 36). Genetic differentiation among disjunct population groups was highly significant (P < 0.001) for both E. microtheca (FST = 0.301–0.383; Dest = 0.756–0.774) and E. rostrata (FST = 0.325–0.346; Dest = 0.628–0.660), and was similar to their differentiation from allied species. These results, including high incidences of private alleles, suggest historical divergence among cryptic taxa within E. microtheca and E. rostrata. Population groups in E. rostrata have recently been taxonomically recognized as two subspecies. Our study suggests that E. microtheca should also be reassessed as two taxa or considered as two ESUs, and the southern occurrence should be listed as Critically Endangered. We suggest a precautionary approach for flora in this and similar landscapes, whereby historically wide geographical disjunctions are assumed to indicate separate units for conservation.