The subgenus Siphisia is characterized by the presence of a 3-lobed gynostemium, whereas subgen. Aristolochia usually presents 5-6 lobes and subgen. Pararistolochia 6-24.
From an evolutionary viewpoint this subgenus is even older and more primitive than the 'classic' subgen. Aristolochia representing 'living fossils' in that context.
Thus subgen. Siphisia is not a species-rich lineage and can be further divided into the following sections only:
restricted to S-China and few adjacent countries.
named by reason of similarities to species of Nepenthes pitcher plants and mainly consisting of highland species from the Himalaya region. According to the latest discoveries its range of occurrence is to be expanded to Vietnam and Hainan.
is distributed across the Japanese Islands, Taiwan etc. but also reaches the Eastern part of China and Vietnam.
interestingly consists of species from Asia (Russia to Indonesia) as well as about two dozen ones from North America.
Mexico is the centre of diversity once again but the southernmost species even reaches Panama.
Recent investigations led to the conclusion these separate distribution hotspots resulted from the colonization of North America via the Bering Strait and extinctions within the last Ice Age leading to the withdrawal to more temperate/tropical areas again.