Astrophytum myriostigma
cv. Onzuka tricostatum

This is a very nice and super selected plant, 3 rounded ribs and very nice V marking.
 

Description: Astrophytum myriostigma cv Onzuka "tricostatum" with only three ribs - is one of the most sought after cacti, that have fabulous markings much like the ‘kabuto’ asterias. There is a variety of variations in ribs shape and in stems markings.
This cultivar tends to be unstable, and some of the three ribbed specimens develop additional ribs as they age. Old and big plants which maintain the typical three ribbed shape are very prized. If you are so inclined you can pay large sums of money for some of the best Japanese forms.
Flowers: arise from the areole at the tip of the stem on mature plant (at least 4-5 years old) they are large, funnel-shaped, yellow, 5-7 cm wide. Blooming intermittently throughout the warm months from spring to autumn.
 

Cultivation: Although regarded as a choice and difficult plant in cultivation it is relatively easy to grow. It is sometime seen as a grafted plant but grows very well on its own roots too. Use mineral well permeable substratum with little organic matter (peat, humus). Water sparingly from March till October and keep perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. (but it is Hardy to -7°C for short periods) In the rest period no high atmospheric humidity!! Sun Exposure: Light shade to full sun.
Be careful: The epidermis of ONZUKA  is harder than in the normal myriostigmas and cracks easily if plants are overwatered.

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

cv. ONZUKA tricostatum

Conservation status: Listed in CITES appendix 2.

Origin:  Japan, Garden origin (Nursery produced cultivar)
 

Etymology: "tricostatum"  just means it has 3 ribs. There are some other varieties of the 3 ribs, such as "nudum tricostatum", "Fukuryiu tricostatum", "Onzuka tricostatum", "Onzuka Fukuryiu tricostatum" etc.
 

A. myriostigma cv. Onzuka tricostatum  fukuryiu
With false ribs between the true ribs.

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

• A. myriostigma
• A. myriostigma bicostatum
• A. myriostigma columnare
• A. myriostigma cv. FUKURYU
• 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 + FUKURYU tricostatum
• A. myriostigma cv. ONZUKA + HAKUUN
• A. myriostigma cv. ONZUKA + KIKKO
• A. myriostigma cv. ONZUKA quadricostatum
• A. myriostigma cv. ONZUKA tricostatum
• 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 type1
• A. myriostigma tricostatum nudum
• A. myriostigma variegatum

Propagation: By seeds, remembering that  seedlings dislike strong light and dry conditions  and need to be repotted frequently. Eventually, as they become mature, they attain a maximum size of 8-10 cm (20) cm in diameter. However, old plants become senile and have a tendency to succumb to disease and a weak root system. At this stage, as is well known, they die suddenly. So, after they reach 10 cm in diameter grow them slowly, and adopt a new repotting period, using intervals of every 2 - 3 years. Additionally grow them under drier conditions or with stronger sunlight.
But plants are often grafted to accelerate growth as they would generally take at least a five years to reach maturity on their own, but the grafted plants are typical rather tall growing, compared with plants on their own roots that are usually more flat to the ground.