This purchase only includes chapter 20 of this title.
Cycas szechuanensis W.C.Cheng & L.K.Fu was not published until 1975, although it was one of the two cycads with the longest cultivation history in China. Some individuals of the species were cultivated for hundreds of years. A comprehensive provenance investigation of C. szechuanensis was carried out in 2011. The survey covered almost all old specimens of the species recorded in literature. Meanwhile, in order to study genetic diversity of this species, 61 samples from 13 locations in four provinces were analyzed using SSR markers. For comparison, we also assessed genetic diversity of 25 samples of C. fairylakea, a closely related species of C. szechuanensis, from 3 locations in three provinces. The results showed that there were no natural populations and male plants of C. szechuanensis left in China and all examined individuals are female. Compared with C. fairylakea, which harbored a moderate level of genetic diversity, C. szechuanensis exhibited little variation, which means that all examined individuals of C. szechuanensis might come from the same mother plant about 400 years ago. For purposes such as religion, folk custom, or gardening, people bred the cycads by suckers or divisions and spread them around and the current distribution pattern was formed. Little variation has been accumulated during hundreds of years of cultivation. Considering that obvious but relatively low genetic differences existed between C. szechuanensis and C. fairylakea, we agree to treat C. fairylakea as a subspecies of C. szechuanensis. According to the codes of nomenclature, C. szechuanensis will be reduced to an autonym C. szechuanensis subsp. szechuanensis. Additionally, according to the criterion of the IUCN Redlist, the protection level of C. szechuanensis subsp. szechuanensis should be upgraded from critically endangered (CR) to extinct in the wild (EW).
Keywords: Cycas szechuanensis, C. szechuanensis subsp. fairylakea, provenance investigation, SSR, genetic diversity