This form has a very characteristic glabrous stem lacking the white tufts of loose hairy scales typical of the common Astrophytum asterias. The smooth green epidermis show up the felty areoles. The plants during cold and dry winter rest often take a nice red coloring.
Common Name:Â Sand Dollar Cactus, Sea Urchin Cactus, Star Cactus, Star Peyote
Habit: It is a solitary (unless damaged) perennial stem succulent growing deep seated just flat to the ground surface. Only in cultivation plants may have a spherical till columnar shape.
Roots: The underground body is fleshy, turnip-like, with fine diffuse roots.
Stem: Non-branched, much depressed, disc-shaped to low dome-shaped, grey-green to dull green (unless stressed), mature plants 2-7 cm tall, 5-16 cm broad, dotted with numerous minuscule tufts of bright white wool (hairy scales). These hairy scales are usually loose, sprinkled over the stem in irregular patterns, sometimes arched around the areoles or on line. Cultivated plants possess sometimes very dense and big hairy scales. The short white wool on surface, said to substitute for lack of shade from spines. There are also completely flake free pure green specimens.
Ribs: The stem is typically divided by very narrow but distinct vertical grooves into 8 broad ribs. The ribs are very low, almost flat on top, forming triangular sections with no cross-grooves. The normal rib number eight is very stable in wild specimens, independent of the age of the plant, but in cultivation selected cultivars and hybrids can have from 4 to 13 ribs.
Areoles: Round, prominent, 3-12 mm in diameters, forming a line up to the center of each rib, felted to hairy, white, creamy, dirty-yellow till straw-colored, then grey. Normally 3 to 10 mm apart, but sometime very close one to each other in cultivated plants.
Spines: Not any. Only seedlings show some rudimentary spines within the first weeks and months.
Flowers: Apical, diurnal, radial, 3-5 cm long, 5-7(-9) cm in diameter opening widely, yellow with orange/red throats. Ovary and tube very short, densely covered with thin, bristle-like, black tipped scales and with cobwebby wool in axils. Outer tepals short, narrow, pointed, greenish, covered with short fuzz on outer surfaces; inner tepals long, slightly spatulate, from narrow orange-red bases; upper parts clear yellow, edges entire, tips entire and slightly pointed to erose and irregular. Filaments orange at bases, yellow above, anthers and pollen yellow. Style yellowish with 10-12 yellowish-green stigma lobes.
Blooming season: In habitat the flowering period is spring and each flower lasts for one or two days only, but the plant may flower at any time during the warmer months of the year if adequate water is provided.
Fruits: Oval to round, about 1,5-2 cm long, green, pinkish or greyish-red densely covered with spines and dull-white wool, becoming dry and finally breaking off at or near base (not opening above the base).
Seeds: Black or dark brown, glossy, bowl to helmet shaped about 2 mm long, 3 mm broad.
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz