Is there any relation between the distribution of these species or is it a coincidence, caused by geological forces? habitats? animals?
My initial research yielded nothing on the topic, maybe one of you know something about it? I doubt I am the first to notice this?
Here are some more that more loosely fit the disjunct distribution but seem to follow more of a cool/wet weather habitat trend and I believe to be separate: https://www.one-tab.com/page/blnHVBbVSdaCNIVVU3ZKwA
I don’t know if this concept applies to your particular cases, but disjunct plant populations in Australia are often an artefact of a historically different climate regime. So you get some taxa with populations on the west and east coasts with nothing in between for thousands of km. That’s because that central zone is arid desert, but thousands of years in the past it was closer in climate and vegetation to the coasts; the plants once had a continuous distribution that was then broken over time with changing conditions
Of course, that is usually how disjunct populations come about. I guess I am wondering the specific cause behind this instance more so the general cause. That Australian distribution pattern sounds neat.
Cool, moist places, climate moderated by nearby adjacent large bodies of water. Add climate between becoming drier with more extreme temperatures, and plant ranges are severed. You might want to discuss this is Dr. Anton Reznicek, emeritus professor at University of Michigan. You can find his e-mail on-line.
Thanks for a fascinating collection of observations! While major geological forces (glaciation, inter-glacials, etc.) may be a major factor contributing to these patterns, is there also the possibility of some sampling “error” or gaps in knowledge? As with many areas, the northern portions of the Canadian provinces inbetween your areas of interest are less well-sampled on iNat than more populated regions to the south. They are certainly not unknown botanically–and I know very little about Canadian phytogeography–but I wonder if there may be at least scattered populations of some of these species in the boreal coniferous forests in the northern portions of those intervening provinces.
I’ve had to consider this very question in my studies of moth distributions in the East and West. Questions like, How close to two closely-related congeneric species occur in forested northern Canada when their U.S. distributions seem to be widely separated?
This is also a trend in the Mogollon Highlands Ecoregion (In Press.) of Arizona and New Mexico. Plant species here isolated sometimes hundreds of miles from where they can typically be found. A good example of this is Rhus ovata.
There are many more well known examples all around the world, for some reason I have a special fondness for distributions affected by the past. Another example of habitats with disjunct/relict species is from Florida where I used to be based is the central florida scrub and the north florida ravines.
I did wonder the effects of sampling, when I looked up range maps outside of iNat, some of the species do seem to suffer from a lack of sampling in other parts of their range but most of those are in the second link(ex. Phacelia franklinii, which also ranges more into washington but doesn’t have observations).
There’s quite a few species that have a east and west coast distribution due to rainfall but this seems to be more localized and related to the lakes climate moderating effects.