Geographic scales of genetic variation amongst Isoëtes in New Zealand

• Genetic analyses were used to identify unique or representative populations.
• Most populations of plants from the 20 lakes were significantly different.
• Populations with known tetraploids were characterised by low genetic variation.
• Water depth of correlated with measures of genetic variation in one lake

Endemic plants of the genus Isoëtes occur as obligate submerged species in freshwater lakes and slow-flowing waterways in New Zealand. Some populations of are under threat or extinct following habitat deterioration. Genetic techniques have been employed to clarify population variation along geographic scales and to focus conservation efforts on unique, or representative populations. plants were sampled from a wide geographic range including lakes on both the North and South Island, with a finer spatial scale (sites and depths within lakes) investigated for four larger lakes within which a larger number of plants could be collected. RAPD (random amplified polymorphic DNA) profiles generated from eight primers were determined for 254 plants from 20 lakes. The majority of the diversity was partitioned between (81%) rather than within populations (19%). Lakes were separated into four clusters (UPGMA), two clusters included only South Island lakes, one comprised a single North Island lake and the fourth cluster included lakes from a wide geographic range. There was a weak correlation between geographic and genetic distance indicating that factors other than isolation by distance determine variation between the populations. As there is a high percentage of genetic variation between populations, the extinction of any population would substantially reduce the total genetic variability for the species. In this context the recognition of the genetically distinct populations of Isoëtes and clustering of lakes has significant implications for their contribution to the conservation of New Zealand Isoëtes as a whole.