Recent phylogenetic studies have placed the extant lineages Amborella, Nymphaeales, and a clade including, Illiciales, Trimenia, and Austrobaileya (the 'ITA clade') near the base of the angiosperm tree. Amborella and ITA members share a suite of ecophysiological and morphological traits related to their occurrence in wet forest understory habitats. In particular, Amborella and ITA members exhibit a variety of growth forms ranging from shrubs to woody vines and a number of physiological traits associated with adaptation to shade. This suggests that angiosperms arose in shady, wet forest understory habitats. In contrast, Nymphaeales possess a suite of ecophysiological features generally associated with sunny to shady aquatic environments. Because these specialized ecophysiological features are closely linked with the aquatic habit, Nymphaeales may represent a separate ecological experiment and thus have little bearing on the ecological circumstances surrounding the origin of the angiosperms. A view of the earliest flowering plants as understory shrubs and vines growing in wet environments differs from previous suggestions that the first angiosperms arose in disturbed, exposed, and semi-arid environments. However, further work on the ecophysiology, phylogenetic relationships, and fossil history of these lineages is necessary to clarify how faithfully the modern representatives of the Amborella and ITA lineages reflect the ecological roles and environmental conditions surrounding the origin of the angiosperms.

Key words: Amborella , basal angiosperms