Isolatocereus (2012)

By Eric Driskill (October 2012)

Isolatocereus was originally described by Michel Scheidweiler in 1837 as Cereus dumortieri. In 1909, Britton and Rose placed it in Lemaireocereus, and about 33 years later, in 1942, Curt Backeberg described the genus Isolatocereus, where it remained until 1961.

For another 30 years, it was placed in Stenocereus. In 1991, Gibson recommended that it be separated back into Isolatocereus. Using DNA sequencing in 1997, Hugo Cota and Robert Wallace found the cactus forms a phylogenetically distinct lineage from Stenocereus. This supports the resurrection of I. dumortieri as a distinct genus.

The name means “isolated cereus,” coined by Backeberg based on a statement Britton and Rose made about the lack of abundance of plants in the wild. The plants are usually large specimens isolated on rocky hills and cliffs. They grow in several areas of central Mexico, with Hidalgo, north of Mexico City, the northernmost site. Isolatocereus grows as far west as Michoacan. South of Mexico City, the plants grow in Morelos, Guerrero and Peublo, and as far south as Oaxaca.

I. dumortieri grow into large candelabralike forms up to 50 feet tall. The blue-green stems, an attractive characteristic of the plant, are 2 to 6 inches in diameter. Stems have five to eight ribs with straight margins. Although the plants have one to four central spines and six to nine radial spines, most of the spines tend to be central, resembling a comb, somewhat similar to an Uebelmannia pectinifera. Flowers are tubular to funnel-shaped, pale green to white, and look similar to Pilosocereus blooms.

This is a very nice columnar plant to consider adding to your collection. It has color, hue and bloom shape similar to Pilosocereus. The spines appear somewhat like a comb. Grown in a pot – even in a greenhouse – the plants will not hit the roof any time soon. They are slow growing and show better body color, spines and shape if grown slowly and with bright light.

Sources:
The Cactus Family – Anderson, E. F. – 2001
Chloroplast DNA evidence for divergence in Ferocactus and its relationships
to North America columnar cacti – Cota, J. H.; and Wallace, R. S. – 1997
CactiGuide.com – http://www.cactiguide.com/cactus/?genus=Isolatocereus