Distribution and ecology of the genus
Geographic location
The habitats of Austrastrophytum are on the Mexican plateau, 800-1800 m above the sea along the western border of the Sierra Madre Oriental. The areas of Septentriastrophytum are 700-1500 m above sea level, north of the Sierra Madre Oriental which beds at Monterrey westward and east of this at the Gulf region up to Texas, USA with only 50-300 meters above the sea.
The southernmost representative of the genus, Astrophytum ornatum, is located in the state of Hidalgo in just a little over 20 degrees north latitude. In the north you find Astrophytum asterias near the Rio Grande, Astrophytum capricorne at Bustamante, Nuevo Leon, and Astrophytum capricorne v. niveum near Cuatro Ciénegas, Coahuila, around 26-27 degrees north latitude. The westernmost habitats of Astrophytum coahuilense are located near Lerdo, Durango. East, near the Gulf of Mexico you find as mentioned Astrophytum asterias. The location of Astrophytum caput-medusae in Nuevo León has been kept secret until today.
Soil and landscape
One finds Astrophytum basically only on calcareous soils and terrain formations with at least partly Cretaceous and Jurassic strata. At a few sites, like Metztitlan, Hidalgo and San Luis Potosí, the capital of the same state, this layering is mixed with rock of volcanic origin. This dark brown to black rock and gravel may not be confused with the metamorphosed limestone of the similar color, which dominates especially in Coahuila. The substrate in the root zone of plants consists mainly of sediments mixed with a bit of humic substances at Austrastrophytum with a higher percentage. In Septentriastrophytum we find next to the sandy proportions clay and little humus, occasionally larger loess inclusions.
The countryside in the south at Astrophytum ornatum is shaped by the rugged canyons and river valleys of the Rio Moctezuma and its tributaries. Astrophytum myriostigma in San Luis Potosi and Tamaulipas inhabits board flat, sandy land, rolling hills and small mountains which appear from a distance often surprising green overgrown. The planes to the Gulf, with some tropical landscape, small, flat elevations with thorn bush vegetation and meadows in shallow depressions that border boulder fields, dominate the landscape from Astrophytum asterias. In turn, Coahuila impresses with wide flat surfaces, deep arroyos, surrounded by majestic mountains and mountain ranges. Astrophytum grow here often in a stunning backdrop.
genus Astrophytum
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