Mammillaria Mercadensis?

[inky]

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Hi all,

I am new to caring for cacti and recently purchased the little cutie above My best guess is that it is a Mammillaria Mercadensis. After making the mistake of potting it in Miracle Gro Cactus mix, I discovered this wonderful group's soil mix advice. I am in the process of acquiring some NAPA 8822 and perlite to make a propper soil. I will be repotting several cacti and as well as some Lithops ASAP. Fortunately, I have NOT watered any of them so they seem to be doing OK in their temporarily incorrect soil conditions. The little bald spot on top was caused by me gently teasing off one of those yucky, hot-glued straw flowers.

Any opinions on the correct identification would be appreciated. THANKS!

[greenknight]

I think M. mercadensis is correct, and the winter flowers fit that ID perfectly. Never grown the species myself, but it's said to be rather rot-prone and needs very well-drained soil - at least 50% grit in the mix. In your humid climate, even more grit and very cautious watering are in order.

Nice plant - I wish I could slap whoever is responsible for glueing a strawflower on it.

[7george]

Mammillaria zeilmanniana ? And there is some synonymity confuse/misuse with M. guillauminiana, M. crinita and so on.

And I agree these "miracle" peat-based mixes are not the best choice for mammillarias. I use mostly mineral ones.

[DaveW]

I agree with George, it's more likely Mammillaria zeilmanniana, probably one of the commonest Mammillaria's you will find on sale in Garden Centres and stores.

A couple of offsets of Mammillaria zeilmanniana Maja sent me last year. The flowers look big as the offsets were only about 1 inch across at the time, which shows how free flowering it is:-

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

Though Mammillaria mercadensis flower colour is variable, but I don't think that's your plant:-

http://mammillarias.net/gallery/mammill ... nsis&lg=uk" onclick="window.open(this.href);return false;

[greenknight]

On the other hand, take a look at these - http://www.llifle.com/Encyclopedia/CACT ... lauminiana" onclick="window.open(this.href);return false;

It could be zeilmanniana, but I would expect it to be producing offsets at that size if it was.

[7george]

It will produce some offsets maybe later this summer, at least mine did at about this size.

The putting of Mammillaria guillauminiana as a variant of M. mercadensis is quite doubtful for me. The description of M. guillauminiana:

Mammillaria guillauminiana Backeberg 1952
Plants solitary or forming clumps. Taproots present. Stems globose, pale green, to 5.5 cm (2.2 in) high and in diameter.
Tubercles conical, axils naked. Central spines 4-5, brown with darker tips, to 6 mm (0.2 in) long, lowermost one
hooked. Radial spines 30-32, bristle-like, white, 6-7 mm (0.2-0.3 in) long. Flowers white with pink midveins, 8-10
mm (0.3-0.4 in) long and in diameter.

is different from the plant in question here.
Was there a taproot? Such plants do not survive in wet peat and are avoided by mass commercial growers.

And M. mercadensis should have lighter flower I think:

sp minutely pubescent, especially the rsp; csp 4(-7), chestnut-brown above, white below, becoming reddish, more
robust than the rsp and twice as long as the others, hooked; rsp 20-30, weak, white; fl pale pink

I do not trust much the systematics of llifle.com...

[greenknight]

The mammillarias.net page DaveW linked to say the flowers of M. mercadensis are "very pale magenta to magenta". While most of the photos of the species are lighter pink, zeilmanniana can also have paler flowers, so that's not definitive.

My first thought was that it was probably zeilmanniana, but I changed my mind after studying it. I could easily be wrong, the two look quite similar and both vary considerably. Time will tell - zeilmanniana is one of the freest-blooming cacti, if it produces lots and lots of flowers you can figure it's a zeilmanniana. The growing instructions are the same in either case.

[inky]

Thanks everyone for the input! I guess I will just have to observe its flower production to find out what I've got.