Achene wall anatomy and surface sculpturing of Lactuca L. and related genera (Compositae: Lactuceae) with notes on their systematic significance

The achene wall anatomy and surface sculpturing of 14 species representing Lactuca L. and related genera were investigated to evaluate inter- and intrageneric relationships. The achene wall anatomy of the studied species can be divided into two types: winged and ribbed. The winged type is present in Lactuca L., Pterocypsela Shih, Cicerbita Wallr., Chaetoseris Shih and Stenoseris Shih, and is characterized by protruding wings and costae in transverse section. Winged type achene mesocarps are composed of parenchymatous cells and fiber cells, and the distinct fibrous strands are confined to the costae or wings of the achenes. The ribbed type is present in Notoseris Shih and Paraprenanthes Chang ex Shih, and is characterized by only having costae in transverse section. Fiber cells are continuous in the costae and intercostae. In surface sculpturing, the ornamentation and the shape of epidermal cells are different among these genera. The results indicate that L. altaica and L. serriola should be conspecific, and that L. dolichophylla is probably an intermediate taxon between Lactuca and Chaetoseris. The results also support the separation of Pterocypsela, Paraprenanthes, Notoseris, Chaetoseris and Stenoseris from Lactuca and Cicerbita as independent entities. Close affinities between Pterocypsela and Lactuca, Paraprenanthes and Notoseris, and Chaetoseris and Stenoseris are also proposed.