M. swinglei hybridization

Several years ago, on a hill northwest of Guaymas, I collected seeds of a mammillaria which I have labelled M. swinglei. This species was very, very plentiful on that particular hill. It was difficult to avoid the plants while walking around. The plants which I grew from the seeds had whitish flowers, often with a somewhat pinkish or brownish midstripe. These plants also had axillary bristles. The first two photos show an example of this M. swinglei in my collection.
I had pollinated the flowers, but this is not really necessary because this species is self-fertile. From the fruits I harvested the seeds and grew plants from it. The young plants looked very similar to the parents, and during the last days there were flowers for the first time on one of these plants. See the third photo. If I would not have known its origin, then I would not have called it M. swinglei, but perhaps M. sheldonii. These plants must be of hybrid origin! I had even sent seeds to the German Mammilaria Society because I was pretty sure that the seed was pure; the seed was put in this years' AfM seed list.

It is quite interesting to note that Reppenhagen writes about M. swinglei that it is distinguished from M. sheldonii because of its mostly white flowers and axillary bristles. The picture in his 2-volume book, however, shows a pink flowering plant!

This example shows how difficult it is to assign a name to a plant. Had I not had the parent plants, I would have labelled the young plants as M. sheldonii or perhaps M. alamensis. A name can only be assigned to an unknown plant if you know who the parents are! For me, this is a reason that I hardly ever respond to ID requests in this forum.

What I have learned from my example is that I will try to prevent hybridizaton in the next year by putting a net over my M. swingleis. It is already too late to do that now, because all the Ancistracanthae are flowering at the moment and bumblebees are flying from one flower ot the other!

Wolter ten Hoeve.

Very interesting, especially with a plant from the M. sheldonii complex. I often wonder about some of these plants, and your experience here prompts me to ask a question about the flower.

In several Mammillaria species, the petals are often paler with a darker midstripe. Sometimes these are just different shades of pink, sometimes the mid stripe is so small that the flower looks almost white. There are examples in the Ancistracanthae as well as others, but M. boolii, M. longiflora and M. insularis come immediately to mind. Is it possible that this is what you are seeing here as well, just natural variation expressed to look different to its parents?

The variability in this M. sheldonii complex is quite amazing really, flower colour perhaps but especially in the central spine(s), its length, colour, hook or straight, or even existence. I grew some sedlings from a straight spined member of the M. sheldonii complex from San Carlos Bay, and they looked when young just like a typical M. sheldonii, with hooked spines etc. I sold most of them as I thought they were hybrids, and just kept one, and this is now producing straight spines. I wish I had kept more.

One day, perhaps, we'll have to genetic studies so that one more input on relationships in this complex can be understood properly.

Well, all 5 original seedling plants (from habitat seed) look very similar. They all have hooked centrals (not a single straight central) and 2 to 4 axillary bristles, which M. swinglei should have. The flowers of all 5 are whitish with a vague brownish to very light-pink midstripe. The plant of the photo had the most pinkish flower. It would be the best to see the plants in flower in habitat in order to see how variable the colour is, and if there are really pink ones present.
The 'hybrid' seedlings have 1 or 2 axillary bristles and the plant body is a bit more open than the body of the 5 original seedling plants, but that could have to do with age. Up to now, only one of these 'hybrid' seedlings has flowered, so hard conclusions cannot yet be drawn, but it is at least remarkable that such a pink flower (almost homogeneous pink, hardly a midstripe visible) did not show up on the 5 original plants.

Wolter.

The flowers of your original plants look much like those of HK277, of which I had a plant with pale flowers, but it is no longer with me, unfortunately. I don't remember checking it for bristles in the axils. I do have 6 cuttings attempting to root down from an old plant, so I may get to see the flowers again.

It'll be interesting when others of the second generation flower!

As an aside, I took seeds from a straight spined "sheldonii" plant at San Carlos Bay in 2010, and sowed them in 2011, I think. The resulting seedlinsg all have hooked spines, so I was disappointed and passed most of them on a just M. sheldonii. I kept one plant, and now it is producing straight spines! The initial hooked spines are still there at the bottom of the plant, but I guess will disappear in time. I don't know whether this is a characteristic of straight spined forms of M. sheldonii, whatever they are named!