Ploidy for this dummy

I am surveying Rosa californica, which I’ve read is tetraploid (n=14). Anyone familiar with the species knows it is wildly variable in prickle form, leaf surface, and hip shape. The only constant seems to be 5 petals and the shape of the buds.

What is involved in confirming the ploidy of a reasonably number of specimens of a species, say 4 to 6, by root tip squash testing? Can one assume hybridity from any unusual ploidy results?

I am especially interested in a thicket with very glandular and fragrant foliage and urceolate hips. I doubt it’s a hybrid because hip productions is profuse.


Cass Bernstein

Hi David,

Yes, it seems like there has been a real break from the rangey growth habit of the earlier persicas. Because of good fertility with modern roses, I think that all of my repeat bloomers are tetraploid.

Cass, is “n” different with R. californica? Usually n=7. I do not have any experience with it, but it sounds very nice.

Jim Sproul

I think it is 4n=28, but i have a feeling that each variation could have the possibility of being different.

Thanks, Jim and Jadae. Sorry for the dummy part. The Jepson Manual treatment states Chromosomes: n=14. I think the intention is to suggest californica is tetraploid. Nutkana is listed n=21, gymnocarpa n=7, so that is my conclusion.

Back to my point. R. californica is widely reported to be both diploid and tetraploid. I’m looking for a way to track which forms and varieties correspond to each ploidy. Is this manageable?

I think mine is tetraploid sheerly by “feel” of it, plus random objective facts.

There is a lot of variability in California species, and there has been a lot of confusion between species. I remember reading about a subspecies that at one time was considered to be a subspecies of R. californica that was later determined to be a subspecies of R. woodsii. Californica is tetraploid; woodsii is diploid. That confusion may have led to reports of diploid californicas.

Cass, it’s interesting that you found a “thicket with very glandular and fragrant foliage”. I found one plant in a californica thicket a few years ago that was truly mossy, with a strong pine fragrance in the foliage and buds. I took cuttings of it, but they didn’t take. I’ve been back to the thicket, but didn’t find the mossy plant. If I ever see it again, I will either dig up the plant, or not take all of the mossy parts of the plant as cuttings.

David Zlesak described the root tip squash procedure that he uses in a past issue of the RHA Newsletter, but I don’t remember which issue it was. You might want to email him. There are also kits that you can buy to do root tip squashes that include everything but the microscope. This one has enough materials to do at least 40 root tip squashes, but I don’t know if it is the best one to use with rose roots:


Thanks, Jim for this new link to the kit. I got the link here to a classroom notes for a lab on how to do root tip squash chromosome counts. I guess I’ll learn how. I’ll do a lab with a young friend who is a molecular cell biologist at Cal who probably did this in junior high school.

I’ll track down the woodsii connection.

I’ve found californica is forgiving of having suckers uprooted. This is a terrible drought year, the soil bone-dry and undiggable. Still, with a small hand-pick it’s possible to dig several canes to a depth of about 6 inches and about 6 inches of stout suckering root. That is more than enough to root several plants. I keep the suckers in deep shade, mounded in 5 gallon pots, misted every once in a while, and they leaf out within three weeks. I don’t cut them back. The plants are grateful for any moisture. They are in a semi-dormant state.

The thicket I found isn’t pine-scented. That’s the normal resinous scent I find. This thicket’s foliage smells like the leaves of Geranium macrorrhizum and its hybrids, which is described as musk-scented. It is powerful, present even after the leaves have been dried for the herbarium. The blooms have slight clove or cinnamon scent. It could be a hybrid. I intend to find out.