Xerophyte

Central Spines

None or one, similar to radials but somewhat longer, with a darker tip and upwards bent when it is present.

Seeds

Shiny brownish-black, spherical up to 1.1 mm in diameter, the surface covered with minute, wartlike tubercles. Hilum oval, flat, with a spongy edge more or less developed according to the populations.

Description

Gymnocalycium nigriareolatumSN|17866]]SN|15765]] has rather strong spines set on darkish areoles, white flowers and bluish fruits. In most of the bibliography it is considered as synonymous of Gymnocalycium hibopleurum, but it has a single bluish-green stem with distinctive black areoles, and dark bluish fruits, unlike of G. hibopleurum, that usually has a clustering habit, clearer areoles and green fruits. Moreover G. nigriareolatum is easily distinguished by the yellow colour of the anthers, which makes it close to Gymnocalycium glaucumSN|15765]]SN|17866]]. The fruit is bluish. The aspect of the plants (length of the spines, shape of the ribs, colour of stems etc..) can vary considerably depending to the local circumstances and in the environment of Cuesta del Portezuelo and Palo Labrado, there are plants intermediate with G. hibopleurum, with green fruits and solitary (not clustering) habit. It could be an intraspecific variation, which seems to be very common in the genus Gymnocalycium. In nature the plants are often attacked by a mould fungus and the areoles develop a characteristic black colouring (hence the species name).

Roots

Napiform, short, strong, often highly branched.

Flowers

Near the apex usually white, with a greenish to reddish throat, but sometimes reddish-pink with a darker throat ( "fa. Carmineum"), broadly funnel-shaped, 45-50 mm long, 35-45 mm in diameter Pericarpel short (12 mm), leaf-green, with rounded scales with a white edge and pink point. The scales pass gradually to the external tepals, while elongating and becoming lighter green. External tepals lanceolate, more or less bent towards the outside, white with a median green stripe and a pink top, the median stripe terminates in a brownish spot. Internal tepals are ivory-white, lanceolate. The throat is carmine. Filaments pink. Anthers yellow. Style greenish-white. Stigma yellowish-white, with 10-12 lobes, under the stamens.

Ribs

8 to 16(-20), regular, straight, divided by transverse furrows into into angular tubercles up to 3cm wide. The tubercles are rather flat and rounded to distinctly pronounced and sharp-edged, with very prominent conical to angular chins below the areoles.

Stem

Solitary rarely with basal shoots ( "var. densispinum"), initially flattened spherical, then sub-spherical, 10-20 cm in diameter, 10-15 cm tall. Glaucous-green to velvety light to dark green reddening in full sun. Apex depressed, woolly, spineless or with young spines.

Radial Spines

5-7-(9), radiating, straight to curved toward the body, whitish-grey or pinkish-grey with a brown to black tip, spreading (more comb-shaped in "var. simoi") measuring up to 30 mm long. Young spines black with an orange-brown base.

Fruits

Light to dark (bluish-) green spherical, vertical, up to 1.5 cm in diameter. The scales have a thin white edge and pink point.

Areoles

Round to oblong, 7 × 8 mm, at first with white to yellowish brown wool that turns grey or black with time in the wild, whilst new areoles developed in culture remain yellowish-white.