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I was sent a grafted split tubercle of Digitostigma (Astrophytum) caput-medusa by a kind collector in Slovenia. These grafts are rather strange in that the new plant does not arise from the tubercle epidermis but from the internal cut surface underneath rather like a piece of tissue culture at first rolling the tubercle to one side.

These links shows the method used and I think "Ariocarpus" in the link is probably the person who sent it me since it was grafted on the same Ferocactus glaucescens stock he uses:-

http://www.cactuscultivars.com/forum/in ... opic=233.0" onclick="window.open(this.href);return false;

http://www.cactuscultivars.com/forum/in ... pic=233.20" onclick="window.open(this.href);return false;

I received the plant in January as just a split grafted tubercle with a tiny nub about match head size appearing at one side in the middle. This is the plant a few weeks ago and now one bud has flowered, therefore has made all this growth since the beginning of the year:-
An interesting method of grafting by splitting a tubercle lengthwise and I wonder if it could be used on other tuberculate cacti, Leuchtenbergia etc?

Interesting!
So how typical is it for cactus grafts to be able to grow, other than from an aereole?
Is this a peculiarity of Astrophytum c-m, or is it quite common?

No idea, most grafts I have seen grow from the areoles or axils but then I have not seen them grafted as split tubercles. Digitostigma's do seem to have the ability to produce flowers from down the tubercle where previously there was no obvious areole. The largest bud in my picture was unusual in that it came from the apical areole whereas you can see the others are from further down.

In the case of the grafted tubercle the new plant did not come from the tubercle epidermis but as tissue from the cut surface underneath. However in tissue culture they do seem at first start as undifferentiated tissue and what pops out from the underside of the tubercle looks very like this, see micro propagation examples at bottom of this link:-

http://www.cactus-art.biz/schede/ASTROP ... edusae.htm" onclick="window.open(this.href);return false;

The above link says flowers do not come from the apical areole and whilst from lower down seems more common, my plant shows they can.

Interesting