Natural hybridization between the endangered herb Artemisia gilvescens (Asteraceae) and the common congener, Artemisia indica var. maximowiczii in Japan

Interspecific hybridization between the endangered herb Artemisia gilvescens and its common congener A. indica var. maximowiczii (Asteraceae) was analyzed using morphometrics and molecular genetic markers [ycf6–psbM spacer in cpDNA and the internal transcribed spacer (ITS) region in nrDNA]. Ninety eight plants from Naruto, Japan, were used to determine morphological and genetic variations. PCRRFLP analysis of the ITS regions revealed that 35, 34, and 29 individuals were A. gilvescens, A. indica var. maximowiczii, and their hybrid, respectively. Based on a principal component analysis of six leaf characters, A. gilvescens and A. indica var. maximowiczii were clearly separated into two clusters. Although many hybrid individuals were plotted in the space between the clusters of A. gilvescens and A. indica var. maximowiczii, seven and three individuals plotted as A. gilvescens and A. indica var. maximowiczii, respectively. We detected both A. gilvescens and A. indica var. maximowiczii haplotypes in the putative hybrid individuals in the cpDNA variation analyses, indicating that an F₁ hybrid was formed in crosses in both directions. The percentage of stainable pollen grains (79.2 ± 22.4%) in the putative F₁ hybrids was comparable to results in the parental species (80.1 ± 10.9% in A. gilvescens and 89.1 ± 12.7% in A. indica var. maximowiczii), suggesting that ongoing extensive introgression might be an extinction risk for A. gilvescens. Ex situ conservation in a botanical garden is highly encouraged to preserve the endangered A. gilvescens.