Frailea cataphracta has 10 to15 low and broad ribs. The tubercles are dull green and flatted above, with a purple-brown lunate (moon shaped) blots situated below the areoles. It is undoubtedly one of the most fascinating cacti.

Family: Cactaceae (Cactus Family)

Subfamily: Cactoideae

Tribe: Notocacteae

Scientific Name: Frailea cataphracta (Dams) Britton & Rose 1922

Britton and Rose established the genus Frailea in 1923 and Frailea cataphracta was made a character species for the newly created genus.

Distribution: Cordilleras of Altos Paraguay, Paraguay and brazil (South America)

Habitat:  Grows in fine sandy-loamy or fine grained but permeable soil often at the edge of sandstone plates. Forms dense colonies in all sizes with over than 200.000 plants. The vegetation consists of grass and small brushes, with no other cacti species present. Most of the Fraileas grow in half shadow under the grasses and brushes and only few are exposed to full sun. Climate is warm and humid. The rainfalls happen all around the year with a relatively high amount of over 1500 mm with much thaw during the night.

Conservation status: Listed in CITES Appendix II

Synonyms:

• Echinocactus cataphractus Dams
  In:  Monatsschr. Kakteenk. 14: 172. 1904 (Original pubblication)
• Echinocactus cataphractus
• Frailea uhligiana
• Frailea cataphractoides
• Frailea matoana
• Frailea melitae

Etymology: The genus name "Frailea" remembers the Spanish "Manuel Fraile", born in 1850 who was responsible for the cactus collection of the Department of Agriculture of the United States at the end of the XIX century.
The species name name "cataphracta", means armoured or mail-clad.

Frailea cataphracta has  10 to15 low and broad ribs. The tubercles are dull green and flatted above, with a purple-brown lunate (moon shaped), blots situated below the areoles.

Description: F. cataphracta is a very small depressed cactus that do usually not sprout in nature, but in culture with age begins to clump around the base and grow oddly. It is undoubtedly one of the most fascinating cacti.
Stem: Dull-green and dark-brown or purplish, globose-flattened 1-2(-4) cm in diameter, deeply imbilicate at apex
Ribs: 10 to 15 with low and broad crescent-shaped tubercles flatted above, with a purple-brown lunate, blots situated below the areoles.
Radial spines: 5-9 straight 1-2 mm long, appressed, yellowish or whitish.
Central spines: Absent.
Flower: Sulphur yellow from the top of the plant, sometimes larger than the plant itself (4cm diameter). But don't be disappointed when the easily produced buds fail to open. Fraileas are cleistogamous meaning that their flowers produce seed without even opening. Without the need for pollination, hence the buds rarely reach full bloom and remain closed. They will open only in great heat in the hottest, brightest, afternoon sun, if at all.
Fruit: Dry indehiscent with scales and bristles that detach easily, pericarp membranous, fragile that break easily releasing the seed.
Seeds: Comparatively large, black and shining, up to 2 mm wide, with a triangular, deeply concave face.

Crests of this species are also known and very beautiful.
 

An unusual developed flower

Buds

Cultivation:  Grow them in rich, porous soil and let them dry out between waterings.  These plants need a minimum temperature of 5-10° C (but occasionally temperatures of a few degrees below 0° are not dangerous)
Sun Exposure:  It enjoys full sun, and it can take on a near black appearance when kept in bright light.  In a shaded position the plants grow faster, but are not flat shaped and dark coloured.
Characteristically, during the dry season plants retract completely under the ground both in the wild and in cultivation too.

Notes: This plant is short living (It does not live long - about 10-15 years).