Pilosocereus armatus

Pilosocereus armatus is a species of flowering plant in the cactus family Cactaceae, native to the Virgin Islands and Puerto Rico.^[1] It was first described by Christoph Friedrich Otto in 1837 as Cereus armatus, and transferred to the genus Pilosocereus in 2021.^[2] It has been treated as Pilosocereus royenii,^[3] and Pilocereus royenii var. armatus is among its many synonyms.^[1] However, P. royenii is a name without a clear application.^[4]

Pilosocereus armatus has bluish green stems with 7–11 ribs. Its branches are usually upright. Areoles have spines up to 6 cm (2.4 in) long and silky hairs up to 4 cm (1.6 in) long. Non-flowering areoles have fewer hairs. The flower is 5–7 cm (2.0–2.8 in) long. The inner perianth segments are pinkish, the outer ones pinkish to pale green. The fruit is red.^[3]

There has been considerable confusion over the correct name for a species of the genus Pilosocereus found in Puerto Rico and the Virgin Islands. Sources have used Pilosocereus royenii, a name based on Linnaeus' Cactus royenii. However, the original description of C. royenii does not make clear its origin and precise identification.^[3][4] In 2019, an attempt was made to validate C. royenii by designating a neotype.^[3] This did not succeed because it did not take into account the earlier designation of a different neotype in 2013, which also failed to make clear its origin and precise identification. The earliest available basionym is Cereus armatus; hence as of June 2025, the accepted name is Pilosocereus armatus.^[4][1]

Pilosocereus armatus is native to Puerto Rico and the Virgin Islands.^[1][3]