Xerophyte

Seeds

Black or dark brown, glossy, bowl to helmet shaped about 2 mm long, 3 mm broad.

Description

Astrophytum asteris (a.k.a. Sea-Urchin Cactus or Sand Dollar) is a well known flat barrel cactus with unique and remarkably beautiful form and no typical covering of spines, but with tiny speckled tuft of hairs less than pinhead-sized.

Roots

The main root is somewhat fleshy with fine diffuse roots.

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.

Crested Growth

The crested form (Astrophytum asteris f. cristata) - despite to its beauty - is very rare and sought after by collectors, for its unique features. There are several crested clones mainly selected by Asian growers.

Spines

Not any.

Ribs

The ribs are very low, almost flat on top with no cross-grooves.

Stem

Fan shaped, somewhat depressed at apex, grey-green to dull green (unless stressed), mature plants up to 30 cm (or more in diameter, 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 clones.

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).

Habit

It is a small low growing crested cactus that will slowly forms tangled groups up to 30 cm (or more ) in diameter with age. The plant tends to grow seated in substrate, but in cultivation it is almost always seen grafted on columnar cacti.

Similar Species

Astrophytum asterias is sometimes confused with peyote (Lophophora williamsiiSN|1117]]SN|1117]]). Both species are spine-less, and peyote often has 8 ribs. However, peyote is bluish-green but has irregularly shaped ribs and lacks the tiny whitish scales.

Note

The stem is said to be suffused with chemical compounds distasteful to herbivores.

Blooming Season

The flowers are unusual and eventually produced only by some clones.

Areoles

Round, prominent, 3-12 mm in diameters, forming a line up to the centre of each rib, felted to hairy, white, creamy, dirty-yellow till straw-coloured, then grey. Normally 3 to 10 mm apart.