This beautiful species is seen in many localities in northern and northeastern Mexico, and appears to be quite variable both vegetatively and in the inflorescence depending on the locality. This species was initially called Agave macroculmis by Dr. Howard Scott Gentry in his Agaves of Continental North America with the type (the plant that the original description was based on) from a plant in the university botanic garden in Palermo, Sicily. This plant did not have the large, fleshy bracts on the stalk just below the inflorescence as seen in plants in northern Mexico (see photos below), and Dr. Gentry dismissed this as a result of the milder climate in Sicily. In 1990, Bernd Ullrich determined the name Agave macroculmis to be a synonym of Agave atrovirens, which occurs in southern Mexico, thereby leaving those plants in the north without a name. Ullrich then proceeded to pay homage to Dr. Gentry by naming this awesome agave after him. If you want to read Ullrich’s original article and to see more pictures, check the agavaceae.com website.
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Having seen these plants in several localities in northern Mexico, I am starting to wonder if it could actually be divided into 3 subspecies.
First, the form on Cerro Potosí is quite stout with relatively short and super wide, dusty green leaves. The following shots are from Cerro Potosí.
Another form found further south along the Sierra Madre Oriental in eastern Mexico is variable with some plants having a more open form, deeper green leaves that are longer and relatively narrower than the plants seen on Cerro Potosí, and others with a denser rosette with deep green leaves. Regardless of the rosette appearance, these plants produce numerous offsets unlike the ones on Cerro Potosí. The next pictures are of plants found in the Sierra Madre Oriental.
Finally, there are plants in the Sierra Patagalana that appear to have mixed genes with Agave asperrima. The leaves on some plants are slightly rough to the touch and the inflorescence is more open.
Following, are several shots of plants in habitat. Some show dramatic color as they die while flowering.