Sect. Siphisia species are known for their disjunct trans-Pacific distribution range. While the northernmost species in Asia reaches the Mandshurian region, the very same in North America is restricted to S-Canada and southwards.
Nevertheless species from both continents share outstanding similarities in morphology which has resulted in several investigations during the past decades.
Interestingly these revealed the two groups are very variable yet closely related and lead to the conclusion they must have conquered America via the Bering Strait to diversify southwards again just like in Asia.
Although many species show a strong resistance regarding colder temperatures, constant humidity and wrong cultivation conditions their diversity hotspots are to be found in the lowland tropics of both SE-Asia and SE-Mexico.
Exceptions prove the rule of course - there's quite a number of frost-resistant highland species scattered across the Himalaya & adjecent regions plus two hardy species from the USA.
Especially regarding the tropical regions more research would be appropriate to understand their outstanding radiation since flower characteristics and plant habits diversify extremely and may justify the separation of new subtaxa.
To provide an easy overview the species names' below are assigned to their respective species' origin and habit, linked to the subpages of the scroll-down menu on the right.