Very true!
Depends on which botanist you talk to. Some have the rat tail radish as a different species, others not. Given that they will readily cross both ways with common radish I’m inclined to think not but, if they are, then the two way crossability is a plus.
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Yeah, and like i said that’s the way I was taught at school. And that’s the common definition on the internet to, for example Nature says on their page defining ‘species’:
A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offspring. Species are characterized by the fact that they are reproductively isolated from other groups, which means that the organisms in one species are incapable of reproducing with organisms in another species.
Source:
species | Learn Science at Scitable.
But then, are you going to say Solanum esculantum, Solanum galapagense, Solanum cheesmaniae, and Solanum pimpinelifolium, are all in fact one single species? Because on that logic, they would be.
That page goes on to say:
Species can also be defined based on a shared evolutionary history and ancestry. This method of defining species is called phylogenetics, which is the study of the evolutionary relationships among organisms.
So, if we go along with the way this concept is used in plant science, I don’t think we can simply stick to the simple idea of whether they can cross or not. Hence the separate but readily crossable tomato species.
Now looking into it more deeply, we may find more reason to not consider them separate species from genetic evidence in papers such as ‘SSR-Sequencing Reveals the Inter- and Intraspecific Genetic Variation and Phylogenetic Relationships among an Extensive Collection of Radish (Raphanus) Germplasm Resources’:
From that paper:
And:
Here’s an article, ‘Identification of genome-wide single-nucleotide polymorphisms among geographically diverse radish accessions’, available to download in full from this page if you’re interested in reading it:
https://www.researchgate.net/figure/Phylogenetic-tree-of-81-representative-radish-accessions-constructed-using-the-maximum_fig2_339351616
And here’s an image from that article on migration:
So there seems to be good reason for designating them as the same species. However, I personally feel the more important thing for us than words, is function - physical attributes. Their roots are no good for eating, and most radishes have their edible root as our main concern. So, functionally, they are significantly different, more so than Solanum esculantum and Solanum pimpinelifolium are from each other, in that regard.
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Yeah, that makes sense! I would say the thing that matters to me most is how well they cross. Physical attributes matter, but when it comes to landraces, knowing which plants are going to share those physical attributes with the next generation of my landrace is important.
For instance, prickly lettuce has nothing in common with lettuce that I want to eat. However, they cross easily. 
Therefore, I consider them the same species, and that’s extremely important because prickly lettuce is a super common weed in my area. Due to the fact that I can’t get rid of all prickly lettuce within breeding distance (I can remove it all from my yard, but not my neighbors’), I’ve decided I just plain don’t want to try to grow a lettuce landrace. I’d be constantly dealing with bitter thorny nasty halfbreeds. Don’t wanna. Instead, I’ll focus on other species for my leafy greens.
So I tend to think it matters a lot whether Rat Tail radish is the same species as radishes grown for roots. If I wanted radish roots just as much as seed pods, I wouldn’t want to grow Rat Tail radishes next to the rest. On the other hand, if I want seed pods only and don’t care about roots, growing them next to each other may be a great idea.
Yeah. Although, if you want some fun, you could cross them then grow out the F1 and F2 in an isolated location away from your rot specialist and pod specialist populations (both of which should also be separated from each other!) and see if you can select for both attributes (plus leaves perhaps). Like I mentioned if you don’t mind the root being smallish, you could try crossing giant rooted ones with large pod ones, and select for:
- acceptable root size
- large pod size and plentiful production
- nicely eatable leaves
Mind you I just thought of another potential drawback - I don’t know if they flower under the same conditions but I wonder, perhaps the rat tail ones have been selected to flower more easily, and the root ones less easily? If that effects the harvests in your climate, that would be a concern too. Though I don’t know if that’s an issue, I don’t know the details.
Suuuper late to this thread, but I’ve been growing Madras Podding Radishes for a few years now, and they are fantastic! Definitely a radish focused on edible pods (not roots or leaves), but they are tough and actually reseed themselves readily here in zone2b. They’re juicy and snappy, and even our pups like to eat them!
I’d be willing to share seed for next year, if you send me a SASE.
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I’ve heard farmers who grow the Rat-Tail for seed say that it is extremely hard to keep it from crossing with other radishes. It’s just a variety bred for tender pods, not a different species.
Excellent! That’s just the information I was looking for! Thank you!
Ooooh, that sounds great. I’ll message you. 
I’ve seen people saying something like, “Slow to bolt” about root-focused radish varieties, as if that’s a good thing, so I suspect most of them are selected for being slow to flower. That said, when I grew French Breakfast radish last year, they started flowering after about 50 days and were giving me delicious pods in about 60-70, and Rat Tail radishes say they’ll give you seed pods in about 60 days, so it may be that they’re not that slow to bolt. Or maybe it was just that I planted them late and they were dealing with July heat. 
I don’t keep precise records so can’t say an exact date, but less than sixty days ago I planted a bunch of radishes. Some of my old landrace mix, some new white daikon type that has smooth fuzz less leaves and some rattail. The rat tail is starting to bolt, the others are not.
Cool! That’s good data!
I should add, the rat tail plants are considerably smaller and less robust. Rather puny by comparison to the others, don’t know what’s up with that, growing conditions are exactly the same for all.
Oh, that’s a shame!
Yeah that’s exactly what I was meaning. But I guess it also depends on when you plant them.
I wonder 2 things:
- Whether the root radishes varieties you grew might have been better suited to your specific conditions than the rat tail variety/varieties you grew.
- Whether you are referring to how they are at the pod producing stage, or prior to that. I wonder for example, if the rat tail ones are smaller, taking up less space, through much of their life, but produce a higher weight of pods, then that would actually be a good thing - more weight in pods per square meter would be ideal, right?
They look nice! Although the pods seem fat but very short compared to the rat tail radishes I posted above. But maybe could be cool to make a landrace with all 3 rat tail radishes posted to this thread, and maybe some others too!
Yeah, the pods on the Madras Podding Radishes remind me of the pods on the French Breakfast radishes I grew last year. They were crisp and juicy, with barely any spice at all. They were delicious both raw and cooked. Yummy.
On the first point, that is quite possible because mine are basically a landrace that have been growing, mostly feral, in my garden for several years.
On the second point, I planted mine and three new types from Baker Creek all together in the same bed at the same time. All of them came up about the same time and are growing nicely except for the rat tail. They are bolting already without having grown much at all and are much smaller than any of the others. They don’t look healthy and there is little chance that I see of them producing much of anything, especially since I will probably just cull them out.
I’m used to radishes whose bloom stalks get four or five feet tall and produce more pods than I know what to do with from just a couple of plants. I usually chop them back, a lot, and depend on staggered planting or rather staggered sprouting of volunteers to extend harvest time.
The one with smooth, fuzz-leaves is doing great, I can’t tell any difference in growth from my own. It’s also the one I most what to add to mine so I’ll be saving lots of seed from it. That fuzz-less trait makes the leaves themselves just as good to eat as the pods, I hope to introduce it to the whole population.
As far as the rat tail, I don’t put up with inferior performance when I try a new variety or crop. Especially like here, when I know for sure it is the variety and not some other factor that accounts for it. It’s not worth the trouble of adjusting my soil, habits or anything else to accommodate them when all others grow fine. So long, rat tails, I don’t think I even what your pollen in my patch.
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Sounds awesome!
I wonder, perhaps the rat tail would have liked to have been planted earlier? So they could establish more energy reserves before bolting? And, if they do produce seed, maybe worth saving the seed and planting again, maybe also with more seed you could experiment with several plantings at different times to see what works best in your conditions? I’m just thinking aloud…
Or… maybe just a different variety would suit your conditions better…
But yeah the pollen issue I can understand, if you can’t grow them far enough away from your rot population.
It might be worth trying another Rat Tail from another source someday, just in case it was only that specific population and not the whole species that was poorly adapted to your climate. Probably the best way to do that would be to keep a casual eye out for a neighbor who grows them, and ask if they have a few spare seeds.
Your radish landrace sounds awesome! 
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I’ve sort of waffled back and forth about the rat tail radishes. After deciding to cull them I ended up leaving some. Partly because the leaves, though not so much as the China Jade, are largely fuzz less. Some of the others are starting to catch up in flowering so I can let them cross, if I want too. But I’ve decided for sure I don’t want to. The smaller ones I culled earlier had no root at all, not surprising but I pulled a couple of larger ones they also had no root at all.
Although I consider the pods as more of the eatable harvest than the roots, we do sometimes enjoy the very large roots that can often be harvested in the fall or early winter, and I also depend on those large roots to rot and improve my soil. I don’t want to screw that up just for the novelty of long skinny pods. So, the rat tail and all current flowers on the rest are really for sure, going away this time.
Now that fuzz-less trait from the China Jade is another story, they are great, and they do make nice big white roots. The more the better of seeds and pollen from them.
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