Comparison of growth characteristics and evaluation of hybridization potential between native and exotic individuals of endangered <i>Geranium robertianum</i> ―Herb Robert Conservation Research Group―

<p>Geranium robertianum is an annual herb of the family Geraniaceae that grows only in limestone areas in Shiga, Gifu, and Tokushima Prefectures in Japan. Because its distribution is restricted to limestone sites, the number of individuals is small, and it is listed as an endangered species in each prefecture. On the other hand, this species has been found growing along roadsides and forest edge throughout Japan. This is thought to be introduced from overseas as an ornamental plant and naturalized. In this study, we collected leaves and seeds of G. robertianum from 26 sites across Japan and conducted MIG-seq analysis, common garden experiments, and crossing experiments to evaluate the degree of genetic differentiation, adaptation, and hybridization potential of native and non-native individulas. The MIG-seq analysis showed that at least two exotic lineages had invaded Japan, with one lineage distributed in cooler regions, mainly in Hokkaido and Tohoku, and the other in warmer regions south of Tohoku. The native lineage showed genetic differentiation among mountain ranges and between low- and high-elevation populations. Morphological differentiation according to elevation was also observed, indicating that they are adapted to their respective growing environment. The exotic individulas produced more seeds than the native individuals under growing conditions with direct sunlight. Crossing experiments between exotic and native individuals produced fertile seeds, so we should take care to ensure that exotic individuals are not introduced into native habitats.</p>