Where do you find plants? Sometimes it seems the clue is in the name. For example, anyone looking for the Radnor Lily in the UK will only find it in Radnorshire. However, sometimes this is misleading. The Radnor Lily, Gagea bohemica, also lives in Mediterranean and Central Europe. It’s an example of a disjunct distribution, where species that are closely related genetically live in geographically distant locations.
Tertiary relict and Arctic/circumboreal distributions are two major patterns of Northern Hemisphere intercontinental disjunctions with very different histories. Tertiary relicts are “survivors from plant communities that were distributed throughout a large part of the Northern Hemisphere during much of the Tertiary (i.e. 65 – 15 million years ago (Ma)).” The plants tend to live on, isolated in warm regions separated after land bridges were lost or mountains rose. Arctic/circumboreal distributions, in contrast, tend to be younger, cold climate species. This is because opportunities for these species arose at the end of the Tertiary as the planet cooled. Each distribution has been well researched, but members of one biome have generally not been incorporated in the biogeographical analyses of the other. Links or transitions between these two biomes have rarely been addressed.
Liu and colleagues generated phylogenies of Chimaphila based on cpDNA and nuclear ITS, using Bayesian and maximum likelihood methods.
The authors conclude: “This study at the genus level indicated a close link between Tertiary relict and circumboreal biota and revealed that the circumboreal forest biome might have an old origin, at least 20 mya. Chimaphila contains a clade of four species with a Tertiary relict distribution, whose two Asian species arrived there independently of one another.”
Milne, R. I., & Abbott, R. J. (2002). The origin and evolution of tertiary relict floras. Advances in Botanical Research, 281–314. https://doi.org/10.1016/S0065-2296(02)38033-9
Liu, Z.-W., Zhou, J., Peng, H., Freudenstein, J. V., & Milne, R. I. (2019). Relationships between Tertiary relict and circumboreal woodland floras: a case study in Chimaphila (Ericaceae). Annals of Botany. https://doi.org/10.1093/aob/mcz018