Found two links:

http://www.rosemagazine.com/pages/yellowrose.asp

http://www.rosegathering.com/china.html

My suspicion is that rose seeds likely spread with bird droppings with birds blown off course in storms.

Since roses aren't terribly tropical, this limited them to the northern hemisphere.

It would also be possible for seeds to survive with plants uprooted in floods then carried across the oceans with tradewinds and currents, with again the tropics proving a barrier against the more temperate seeds.

Which is a reasonable theory, though begs the quesiton of whether Eurasia or North America had the seeds first.

As for possums, North America has lots of the big ugly-looking things (I almost ran into one a couple weeks ago going a block or two away), and that doesn't stop rosa rugosa from colonizing wherever.

Some of the toughest roses around are from Asia. Arnold Arboretum's rose collection (Jamaica Plain, Boston, if there are people who like horticulture coming to Noreascon 4, it's a good place to visit) includes some from places like Siberia, I thnk, and those things are -extremely- aggressive growers (have impressive thorniness, too).

One of these days Real Soon Now I am going to pay a visit to Nor'east Roses which is in Rowley. The place grows miniature roses. Their "Scentsation" family is EXTREMELY fragrant. Don't leave them for very long in a car, I made that mistake when I was working around the corner from where the New England branch of the Rose Society has its garden and was having its annual plant sale in May or late April. I bought three or four Scentsation plants, which were in book, and left them in the car in the parking lot for an hour or two while I was in the office, may have run some errand after then, and then went home--with the windows DOWN and getting a migraine from overdose of rose perfume. It was THREE DAYS before I could drive the car without having to have the windows rolled down!

http://www.noreast-miniroses.com/bin/nemr2003.cgi

(Btw, ever read "Guns, Germs, and Steel"? Most domesticatable (sp?) plants arose (ahem) on the 'Eurasian' continent. That might be why.)

My first thought was that there was something in South America that could outcompete roses. However, it stands to reason that if something could outcompete roses in the same niche there, they'd outcompete roses in the north eventually as well (see marsupial extinctions). So scratch that.

I checked into the pollinators of roses, but there's nothing special there. I thought, maybe they rely upon migratory pollinators, like monarchs or something. No go there either.

So what's the main difference between the north and south hemisphere, I have to ask. As far as I know, it's mostly just a reversed seasonality. When one is winter, the other is summer.

So I suspect that roses were, for whatever genetic reason, never able to alter their flowering season to match the southern hemisphere, so they were flowering ( or not flowering at all) when pollinators were available. So due to the seasons, they couldn't reproduce, and never took hold.

With modern breeding and the assistance of humans, we've been able to adjust the rose's blooming season, perhaps.

That's my guess. I'm checking with some botanists I know to see what they think.

It can get from there to NorAM, via the Berring Land Bridge, but only in alpine species that have trouble spreading once they're here.

It can't get from there to Africa, because there's this great big desert and then a bunch of tropical jungle in the way. (Pretty much all roses are temperate plants, right? So even though the Sahara wasn't there until relatively recently, thre's still the problem of not growing anymore where the Sahara is, and not having got past the jungles to grow in Southern Africa.)

It can't get to Australia or Malasia because there's an ocean in the way, and the Eurasian side of the ocean is an unsuitable biomome for the roses to be in in the first place.

It can't get to South America because propagating southward through NorAm means propagating through a bunch of climate bands and then across arid highlands and a narrow isthmus full of tropical jungles. (Human farmers had and have trouble moving plants around North/South in NorAm.)

So the rose must stay home, until these people with ships start shifting them into suitable habitat, I think.

Modern times has these people in ships, who are the plant kingdom's best friend in terms of worldwide propagation of successful species.

Give it enough time and there will be native Australian, African and South American roses, the same way we have Native Americans--it's not that they originated here, but they've been here so long that you need archeology to prove it.

No one's sure if they're an ice age leftover, an early deliberate introduction by natives, or what.

Oh, and someone was propagating it as a nursery tree, I think with an eye to adding it to the set of street trees.

Translation, rose spread over the land bridge didn't have to be alpine species. I don't recall seeing roses growing up at Thule--grass, poppies, and even what I figured out much later on had to be an artic willow, literally clinging for dear life to a rock (the winds at Thule are second only to the top of Mt Washington)to avoid being blown away-- but nothing that looked like a rose/had thorns.

Alpine plant species tend to be small things--the larger a plant, the more susceptible is it getting blown away, dying of exposure, etc.

I wonder, what was the farthest south that roses had been found before human intervention in recent centuries -- were there roses in North Africa? And how far south was their "natural" range in the Americas?

Would this be contradicted by the fact that in Northern California my roses bloomed all year round?

MKK

I'm heading toward a BS in "plant biology", since the University of Washington no longer has a botany department, but I didn't have any botany courses this quarter, so thanks for the question. My answer is "Give them time." The Rosaceae are a fairly recent evolutionary development, and, as people have been saying, right now they mostly like to live in temperate regions. Unlike the Asteraceae, which are also a young family but often have windborne seeds, most Rosaceae seeds are distributed by animals due to some really nifty fruit types. So, while the Rosaceae are very successful, you don't tend to find them jumping quite as far. Birds migrate, but they certainly don't keep their gut contents with them the whole time.

And if you're just talking about the genus Rosa, that's 2x10^2 species instead of 2x10^3 species, and the chances of one of them adapting all the way through tropicality and back to temperate life are that much less. Guns, Germs, and Steel is a pretty good reference for that sort of thing, as Yahmdallah said, though it doesn't go into much detail.

The book I used for species counts and to confirm my recollection of trends in the family was Wendy B. Zomlefer's Guide to Flowering Plant Families, which is a wonderful taxonomy resource. I think it cost me about $75, but it's a wonderful resource.

I was in Hebrew school with her and her cousin Barbara, and worked summers in the lab at the plastics plant her father Jack Zomlefer founded and owned (he went to college at University of Chicago intending on studying to become a rabbi, but he took a chemisty class and Chemistry reached out and grabbed him: "You are NOT going to be a rabbi, you are going to be a Chemist!" He wound up with a doctorate in it, invented a number of chemical processes, and landed in Leominster, original home of the plastics industry in the USA, founding Solar Chemical Corporation and becoming a very wealthy man. One couldn't tell it from his house, though, which was a small Cape-style home, unlike e.g. the Doyle Estate (which wound up being donated to The Nature Conservancy by their heirs who'd moved away from Leominster) owned by the Doyle family which had the Doyle Works of Dupont in Leominster. Almost all the plastics industry left the area years ago, and all the Zomlefers except Jack's brother's widow left the area, too (none of them went into the plastics business, even before it left Leominster. Wendy went into botany, which was a complete non-surprise). She stayed because she's like Debra Doyle--someone born and raised in Texas who hates hot weather. There are maybe a dozen Zomlefers in the world.)

If anyone knows a good site for things like which plant families are older than others, and whether legumes are more closely related to mints than they are to Scrophularaceae, I'd be fascinated. Everything is out there, but it can be hard to find.

Dawn

Epacris is the type-genus of the family Epacridaceae, called the Southern Heaths - closely related in a number of ways to the Ericaceae (Heath family), but there are very few of those below the Equator (only one species in the whole of Australia, found on a couple of mountaintops), and no (? I think) Epacrids in the North. There are similar disjunctions in a number of plants & animals.

On other fronts:

R. acicularis is indeed, as far as I know, found into zone 2, and there is a rumor that the ploidy tends to increase with latitude -- that plants native to temperate regions are typically diploid or tetraploid, while plants from the Arctic are sometimes hexaploid or octoploid. I haven't had an opportunity to test this conjecture, and I don't recall seeing any confirmation of it, just the naked claim. Makes me wanna learn how to do chromosome counts (and DNA fingerprinting), y'know?

I was going to blather more; but maybe I should let it go at that, unless someone wants the names of more extremely hardy spp, or wants to grow roses in bogs, or....

Cheers --
jon