Frankia strains are actinomycetes that fix N-2 in root nodules of plan
ts classified in eight families of the Angiospermae. The wide variety
of plants infected has raised questions about the ecology and diversit
y of Frankia symbionts, and their co-evolution with actinorhizal plant
s. Partial sequencing was done of the small subunit (16S) rRNA gene fr
om Frankia endophytes present in the root nodules of Alnus cordata, A.
glutinosa, A. viridis, Casuarina equisetifolia, Coriaria arborea, C.
plumosa, and Elaeagnus pungens growing in New Zealand. With the except
ions of the Coriaria spp., all of the plants are exotic to New Zealand
. Analysis of the 16S rRNA gene indicates that the exotic species were
nodulated by Frankia strains that cluster with strain groups previous
ly shown to be typical for each actinorhizal host. Frankia in 12 nativ
e Coriaria spp. nodules yielded two sequences differing in only one po
sition, suggesting a relatively low diversity compared with the exotic
species.