Pilosocereus

Pilosocereus (from Latin, "hairy cereus") is a genus of cactus native to the Neotropics. Tree cactus is a common name for Pilosocereus species.^[3] The genus Pseudopilocereus is a synonym of this genus.^[1] For many years, the illegitimate name Pilocereus was used for this genus, although properly a synonym for Cephalocereus.^[4]

The commonly cultivated Pilosocereus pachycladus (syn. Pilosocereus azureus) is a blue cactus with hairy areoles that emit golden spines.

When mature, most species develop a hairy lateral cephalium either white, golden, brown, or golden brown. A noteworthy example of an exception to this rule is that of Pilosocereus pentaedrophorus. Generally, tubular flowers emerge year-round from the hairy cephalium. These flowers emit off-putting smells attracting flies and bats for pollination. Flowers come in white, pink, and purple too. Generally, Pilosocereus flowers are self pollinating, but there may be exceptions. After pollination, globose fruits an inch or bigger form. When ripe, they split and reveal their red pulp. Pilosocereus are generally dispersed by bats.

The taxonomic history of the genus name Pilosocereus is somewhat complicated. In 1838, Charles Antoine Lemaire created a section within the genus Cereus, C. sect. Cephalophori, based on Cereus senilis and C. columna-trajani. In the same year, Ludwig Pfeiffer published the genus name Cephalocereus, also based on Cereus senilis. In 1839, Lemaire raised his Cereus sect. Cephalophori to a genus under the name Pilocereus, presumably unaware of Pfeiffer's earlier name. Since both Cephalocereus and Pilocereus are based on the same type (i.e. Cereus senilis), the later of the two names is superfluous, and so must be rejected under the International Code of Nomenclature for algae, fungi, and plants (ICNafp).^[4] In 1894, Karl Moritz Schumann decided that Lemaire's Cereus sect. Cephalophori needed to be split into two genera, rather than treated as one genus. He retained Pfeiffer's Cephalocereus, and attempted to use Pilocereus for the other.^[5] Schumann removed from Pilocereus both of the species originally designated by Lemaire; however, this is not allowed by the ICNafp which requires that a name is permanently attached to its type, so Pilocereus sensu Schumann is equally illegitimate.^[4]

Subsequently, the genus name Pilocereus was widely used and several attempts were made to legitimize it. One possible solution would have been to conserve Schumann's name against Lemaire's. However, a proposal to do so was not accepted by the 1954 International Botanical Congress.^[4] In 1957, Ronald Stewart Byles and Gordon Rowley provided a solution by publishing Pilosocereus with the type species Pilocereus leucocephalus (which thus became Pilosocereus leucocephalus). They also provided names in Pilosocereus for all the species then placed in Pilocereus.^[6]

As of June 2025, Plants of the World Online accepted the following species:^[1]

• Media related to Pilosocereus at Wikimedia Commons
• Data related to Pilosocereus at Wikispecies