Grooved tubercle?

[loyall]

Not sure where to post his question, so here it is in the General forum. The description of the genus Coryphantha in CactiGuide says, "...small, globose plants that have grooved tubercles instead of ribs." I have perused the photos of Coryphantha, and I do not see these grooved tubercles. Can someone tell me what to look for, and possibly show a photo of a grooved tubercle? I suspect my problem may be that I do not understand what I am looking for.

[mmcavall]

I've just stumbled on this term while trying to identify my Coryphanthas. I'm not sure what is a grooved tubercle. But observing my plant I noticed something that is indeed different from a Mammillaria, for example.
Look at the picture below. Note that there is wool (the white stuf) going from the axil of the tubercle to the tip of it. It is like a "sulcate" tubercle, the "sulcus" filled with wool. (Sorry, I'm probably inventing new words...its hard to explain).Try to see it in the picture. Again,not sure it is the groove in the tubercle, but is a distinctive characteristic.

It is easy to see it in the tubercle at the positions 5 o' clock or 11 o'clock.

20220226_122937_copy_768x1024.jpg (98.01 KiB) Viewed 745 times

[greenknight]

An excellent example! The grooves are not usually filled with wool, so not this easy to see. Sometimes quite hard to distinguish, in fact, but this is what you look for - a groove in the upper side of the tubercle, from the axil to the areole.

[loyall]

Thanks guys. I get the idea now. I appreciate both your assistance.

[DaveW]

Basically as I understand it is originally an extended areole where the spiny part has remained on the top of the tubercle but the flowering part migrated to the axils

https://www.jstor.org/stable/2439372

[loyall]

Thank you DaveW for the link to the article on false ariole dimorphism in Coryphantha.

[7george]

Grooves appear at upper part of tubercles of mature plants. Young cacti or offsets have smooth ones like Mammillaria or other genera.
The same with Escobaria.

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