Huh! I assumed all ground cherries were sweet and all tomatillos were savory. Is this not the case?
There are sweet tomatillos (given that the species boundaries for tomatillo are fuzzy for botanists as I understand it). What I’m referring to are varieties of tomatillo larger than anything commonly called ground cherry, but sweeter than any typical green tomatillo. The Malinalca landrace and the Queen of Malinalca which was selected from it is one with a distinctive variety name.
There is also one or more landrace of relatively sweet tomatillos that tend to be purplish, and are sometimes sold with generic names like ‘purple milpero’ or just ‘milpero’. ‘Morado tomatillo’ which is somewhat common on seed racks in my area, may refer to one or more varieties, may be selected from the ‘purple milpero’ landrace. Lots of ‘maybes’ in what I’m writing – this is my own original research, and I’ve cobbled together my understanding from a variety of sources. Could be a little wrong!
I will probably have some Queen of Malinalco this year (fingers crossed) and I will probably not have any purple milpero tomatillo (I made a mistake caring for my seedlings).
On the ground cherry side, there are ground cherries that I would describe as sweet but musky. I’m not sure if there are any truly savory ones, but that’s the kind of discussion that I’d love to have here in this thread if anyone knows more! 
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I grow two populations of tomatillos.
I selected one for super-sweet fruits. Size measures around 2" in diameter. They turn yellow when ripe, and some may have purple flesh or skin.
The other grows feral. The fruits taste sour. Size measures around 2.5". They remain green.
That’s extremely cool!
That sounds like a great reason to have separate sweet and savory packets of tomatillos.
Can sweet tomatillos cross with ground cherries? If not (or if it’s possible, but exceedingly uncommon), I think it’s best to keep sweet tomatillos in a separate packet from ground cherries.
I spent a few weeks reading everything I could about interspecific crosses within Physalis when I was working on some of those parts of Wikipedia and planning my garden over the last winter, but it has completely disappeared from my brain in terms of detail.
It will probably come back to me, or I will read Wikipedia and be reminded, but my overall sense is that:
- it hasn’t been widely studied
- there is a lot of anecdotal information about interspecific physalis crosses
- there are certain interspecific crosses that have been more documented, and there are barriers to viability in F2, but evidence from some wild populations that given enough opportunity, there may be fertile offspring
In a really general way, it gives me the same impression as with the various tomato species. There are some combinations that are much more likely to cross than others, but there is a lot of latent potential for crosses within the genus.
I hope someone more qualified than a Physalis Wikipedia editor will weigh in too 
Edit: Oh yeah, for example the species in Physalis are listed by their subgenera which will tend to help locate the more likely interspecific crosses Physalis - Wikipedia
I also tried to find answer to this question and really couldn’t find much. Either it’s not been studied much or it doesn’t happen. Based on that I felt like I didn’t need to worry about it. Also researced ground cherries and based on one uni lecture they seem to cross quite freely. There were some examples of which species cross, but no clear map like there is of capsicum. I have made crosses to p.angulata with p.pruinoisa and p.pubescens that look like they took without issues. Now that I looked at that wikipedia list I noticed that tomatillo is in the same group with p.angulata, which makes sense since they look similar. I thought I might try to make manual cross just for the sake of it. Maybe not so much to see if it works, but rather to see it doesn’t work. It would make me more confident that those ground cherry crosses were actually real if emasculated flowers don’t pollinate without correct pollen. It all felt so easy.
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I just placed an order for Aunt Molly’s. The best deal I have found so far is with Holmes seed company. They have it available at $6 per thousand. I have seen it available elsewhere at 50-200 seeds in the $3 to $5 range. I plan to use this opportunity to stock up on enough quantity for a big direct seed effort next March or April.
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It does seem like tomatillo might be able to cross with several other members of the Physalis genus, according to The Cytotaxonomy and Genetics of Physalis (1951) https://www.jstor.org/stable/3143331
There is free open access, @JesseI I feel like this might be interesting enough to you that I’m tagging you. There are some notes about how some of their interspecific Physalis crosses that they did grow out, not necessarily tomatillo, didn’t seem to have characteristics of both parents, which needed further investigation.
I didn’t remember anything this comprehensive about Physalis self-pollination and crossing, even though it doesn’t go as far down the rabbit hole as I would like, it seems useful.
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That is more comprehensive that I could find. Most were just some species of ground cherries, but the feel I got watching one youtube lecture is that ground cherries will easily cross and that’s why at some places it might be hard to make distinction if one is cross or some subspecies. Did that say anything about whether tomatillo crosses were by embrio rescue or natural crosses? I remember eggplants and it’s relatives could get wide variety of crosses with embrio rescue, but very few naturally. Is that first column % succes with crosses?
There is a rightmost column with a heading I didn’t get into the screenshot. It represents viable hybrids that the researchers grew out and felt had obvious indications of a successful cross.
Therefore, the fact that there are no entries on that far right column for P. Ixocarpa reflects that they did not get any viable seeds that grew all the way out. Maybe a clue that embryo rescue would be useful, but I don’t think this project attempted it on their crosses.
Ok, so it’s more like what I gathered from earlier googling that lack of info meant they don’t cross freely, atleast with the most likely suspects. It’s kinda reassuring for change to have something like tomatillo that you don’t have to think whether it crosses with other species or selfpollinates. It and bees do all the work. What’s left for me is selecting.
For this year, I designed some Physalis “crossing blocks” which were composed of a tray of five Physalis starts believed to be different species, one of them a sweet tomatillo, one of them perennial, and each with different physical characteristics.
The plan was to plant these clusters far from each other, including two offsite with friends. Life intervened and I was not able to do this, the starts accidentally dried out, and now I’m working in a much more casual way.
What I would like to have is a sweet tomatillo that is known to not self-pollinate that I could use this way in the future. Put it in a cluster of ground cherries and see if any seeds appear on the sweet tomatillo. I don’t have any tomatillos that I know to have this attribute, but perhaps that should be the the first phase of my project before I get into making interspecific breeding sets again.
The way I understand is that tomatillos always need other plant to pollinate. One online lecture I watched on youtube had couple quite excited scientists when they had made variety that actually self pollinates. Maybe self pollination can come as epigenetic change because of conditions (lack of pollination). Then it might be quite hard to actually determine if variety actually isn’t self pollinating. Or would need a grow-out next year to see.
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Thank you that is a good lead for me to learn more!
I planted P. peruvianum this spring. Only one plant got established. Presuming it’s self-incompatible, then any seeds that it makes will be crosses with GTS ground cherry grex, or my tomatillos. It’s always so long season for me, that it might not mature fruits at all.
I have thought they are self-compatible and my experience seems to suggest that as well. They haven’t had any problem setting the first fruits, unlike tomatillo that took couple weeks before bumblebees got their work schedule right.
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If that is true, I am very excited about the 20 or so seeds I saved from the tomatillo plant that I grew next to the ground cherries by mistake. As far as I am aware, only one tomatillo plant was there, a green variety. I managed to get a couple fruits before its size and lack of productivity annoyed me which caused its premature demise.
Most likely just found a way to selfpollinate. I have heard before people having one plant produce and I’m not sure if first time I grew that I had more than one plant that did eventially after a while produce some. Atleast in tomatoes there are self-compatible populations in species that generally are self-incompatible so there must be a way even those can switch if they really need to. Easy to see that kinda adaption to arise at some point as other way they don’t make seed and are eliminated. It may then be deactivated if there isn’t need for it as outcrossing is a lot better for population health. If you really want them to produce having more than one plant is the way to go.
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In many species, the self-incompatible mechanism works like only 99.5% of the time, so selfing may occur, even though super rare. That damned fuzzy biology that gets in our way of saying always/never. Yup. Chaos rules.
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I don’t mean to change the subject too much :), but how do we save seeds for ground cherries? I’ve gotten my first 2. Do you just pull them out and dry them or do we put them in water for a couple of days let them mold and then dry them like tomatoes?