Astrophytum myriostigma var. nudum
This form is without the white tufted characteristics, so it is 'nude', which in this case means smooth green. 
 

Description: A. myriostigma nudum is very similar to the other myriostigma, it only deviate from the well-known typical form for lacking or mostly lacking white flecks, giving a bright green, blue-green,  gray-green or mauve-green color overall depending on clones.
It is by some considered an extreme form of the subspecies potosinus.
Stem: Spherical to shortly columnar with age.  The stems is smooth and can be over 120 cm tall and 5-10 cm in diameter and are shaped like a bishop's headpiece or a star.
Spines: None.
Ribs: The number of ribs vary from 3 to 8 (usually 5).
Flowers: 5 cm in length, pale-yellow, silk-shining unlike the white-spotted plant, occasionally with an orange gloom.
Blooming season: Spring or early summer, They take up to 6 years to bloom.
Fruit: Dry, dehisces towards the apex forming about 5 star shaped lobes. With few seeds.
 

A form with white woolly areoles.

 

A. myriostigma (ssp. potosinum) forma nuda

 

Blooms are like those of the standard myriostigmas
 

The nice cultivar "Maiden's blush"
 

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Astrophytum myriostigma v. nudum (R.Mey.) Backeberg

Scientific name:  Astrophytum myriostigma Lemaire
Original description: Cactacearum Genera nova Speciesque novae et omnium in Horto Monvillano cultarum: 4-6 1839

Origin:  San Luis Potosi, Mexique but many of the clones actually in cultivation are of garden origin (Nursery produced cultivar)

Conservation status: Listed in CITES appendix 2.

Astrophytum myriostigma (ssp. potosinum) forma nuda
 

Cultivation: Although regarded as a choice and difficult plant is not too difficult in a greenhouse, although grows quite slowly. It is sometime seen as a grafted plant but grows very well on its own roots too. Use mineral well permeable mineral soil with little organic matter (peat, humus). Water sparingly from March till October (weekly during summertime, if the weather is sunny enoughand) , with a little fertilizer added. keep perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. (but it is relatively cold resistant and hardy to -7° (-10°)C for short periods) In the rest period no high atmospheric humidity!! They need light shade to full sun this help to keep the plants healthy, although slow growth.
 
Propagation: Almost exclusively by seed that germinate rapidly. Plants are sometimes grafted onto column-shaped cacti.

Photo of conspecific taxa, varieties, forms and cultivars of Astrophytum myriostigma:

• A. myriostigma
• A. myriostigma bicostatum
• A. myriostigma columnare
• A. myriostigma cv. FUKURYU (type A)
• A. myriostigma cv. FUKURYU (type B)
• A. myriostigma cv. FUKURYU (type B) nudum variegata.
• A. myriostigma cv. HAKUUN
• A. myriostigma cv. HAKUUN nudum
• A. myriostigma cv. HAKUUN nudum forma cristata
• A. myriostigma cv. HAKUUN tricostatum
• A. myriostigma cv. HUBOKI
• A. myriostigma cv. HUBUKI
• A. myriostigma cv. KIKKO
• A. myriostigma cv. KIKKO nudum
• A. myriostigma cv. LAIMAKE
• A. myriostigma cv. LOTUSLAND
• A. myriostigma maculatus forma cristata
• A. myriostigma multicostatum
• A. myriostigma nudum
• A. myriostigma nudum forma cristata
• A. myriostigma nudum forma variegata
• A. myriostigma nudum cv MAIDEN BLUSH
• A. myriostigma cv. ONZUKA
• A. myriostigma cv. ONZUKA ball type
• A. myriostigma cv. ONZUKA columnare
• A. myriostigma cv. ONZUKA cristata
• A. myriostigma cv. ONZUKA + HAKUUN
• A. myriostigma cv. ONZUKA + KIKKO
• A. myriostigma cv. ONZUKA quadricostatum
• A. myriostigma cv. ONZUKA tricostatum
• A. myriostigma cv. ONZUKA tricostatum + FUKURYU (type A)
• A. myriostigma cv. ONZUKA white form
• A. myriostigma quadricostatum
• A. myriostigma quadricostatum nudum
• A. myriostigma v. strongylogonum
• A. myriostigma v. strongylogonum cv. COSTA
• A. myriostigma tricostatum
• A. myriostigma tricostatum FUKURYU (type A)
• A. myriostigma tricostatum nudum
• A. myriostigma variegatum