I want a list of extant plant genera that were present on every continent, except Antarctica, prior to the rise of anatomically modern humans, ~100k years ago. I think that list probably includes....
Well, firstly, there were mosses and ferns that evolved in the Devonian, Carboniferous, and Permian eras:
Cystopteris (bladderfern)
Equisetum (horsetail fern)
Isoetes (quillwort)
Lycopodiella (bog clubmoss)
Lycopodium (common clubmoss)
Pteridium (bracken fern)
Selaginella (spikemoss)
There were other plants in those eras like scale trees and seed ferns, but they're extinct now and this list isn't for quitters. Also, there were some moss and fern plants before the Devonian era, but I think they're all extinct.
Next are some much more recently evolved plant genera for which the internet claims at least one species is native to every continent but Antarctica:
Ilex (holly)
Euphorbia (spurge)
Ranunculus (buttercup)
Typha (bulrush/cattail)
Zanthoxylum (prickly ash)
.
Why are they on all of the continents if they evolved after the continents drifted to their current positions? I dunno. Maybe they're good at spreading their seeds on the wind or the water or bird feet or bee legs or fish poop.
I'm probably missing some other non-vascular plants in the list, like genera of liverworts and hornworts. (Edit: The liverwort genus Marchantia and the hornwort genus Anthoceros are both cosmopolitan.) Also, it's super weird to me that there aren't any conifers on the list yet. Like, {Abies, Cedrus, Pseudotsuga, Tsuga, Sequoia, Pinus} - none of those are natively cosmopolitan, if I remember correctly. I'm running out of conifers.
Some honorable mentions: Ginkgo and Magnolia and Metasequoia (dawn redwood) are quite ancient plant genera (late Permian to Triassic), and we know from fossils that they used to be distributed all over North America, Europe, and Asia. Maybe they were also found in South America, Africa, and Australia/Oceania, but we just haven't found fossils there yet? Or maybe they weren't. Fun fact, the dawn redwood was only known through fossils until 1944, when we found some in Japan.
Also from the fossil record, I think we can say that Cycads used to be everywhere but Europe. They're like stubby palms, kind of, if you're not familiar. Cycads include several genera, and I don't know them very well, but maybe one genus or another was once cosmopolitan, except for Europe and Antarctica, and might still be, except for Europe and Antarctica, for all I know.
Before written history, but not so far back as the fossil record, I think Berberis (barberry) was everywhere but Australia; Aristolochia (Dutchman's pipe) was everywhere but Australia; and Papaver (poppy) was everywhere but South America. I'd be upset with Australia for not having any normal plants, but then I remember Wollemia. Do you know Wollemia? It's is a genus of coniferous trees that was only known by fossils until 1994, when we found some in Australia. Australia might not have normal plants, but it has some great plants.
Finally, Ephedra is a very old genus, and Ephedra species are currently considered native to every continent but Australia, and a fossil of a plant closely related to Ephedra was once found in Australia ("New ephedroid plant from the Lower Cretaceous Koonwarra Fossil Bed, Victoria, Australia" (Krassilov et al., 1998)), so I'd guess that Ephedra once had a cosmopolitan distribution, and it's still an honorable mention today.
If you have more good suggestions, I'd like to hear them.
