Discussion
Our study produced a high-quality genome of a shade-loving plant,M. pygmaea , with potential horticulture use. Our analysis revealed that M. pygmaea is very similar to the ancestral genome PCK (Lysak et al., 2016; Schranz et al., 2006). Four chromosomes, AK1, AK4, AK7 and AK6/8, are shared between Megadenia and PCK. The fifth chromosome (Mp5) is similar to PCK’s chromosome AK5/8/6, but differentiated by a 9.92-Mb paracentric inversion. The sixth chromosome (Mp6) was derived from ancestral chromosomes AK2 and AK3 via an end-to-end translocation. Therefore, M. pygmaea has a relatively simple karyotype structurally resembling PCK but with one fewer chromosome, which most likely preceded its independent divergence and later intrageneric diversification (Artyukova et al., 2014). Further research is needed to elucidate whether an ancestral genome ofMegadenia was derived from PCK or another, structurally similar, ancestral genome. A more comprehensive sampling of extant M. pygmaea populations would reveal more details about the closest relatives of this genus. This newly described, high-quality M. pygmaea reference genome will be a valuable resource for further horticultural research and breeding, as well as for research focused on the evolutionary trajectory and biogeography of Megadenia .