Arrojadoa

Arrojadoa
File:Arrojadoa.jpg
Kingdom	Plantae
Family	Cactaceae
Subfamily	Cactoideae
Tribe	Cereeae
SubTribe	Cereinae
Genus	Arrojadoa
Species
Notes	Taxonomy follows Joël Lodé (2015).

Etymology

The genus is dedicated to Dr. Miguel Arrojado Lisboa (1872-1932), who was the superintendent of the Brazilian Railroads at the time Britton & Rose described the genus in his honor in 1920.

Description

Arrojadoa is a genus with solitary or branched stems appearing from the base. The stems are more or less slender, and can be erect, pendulous, or sometimes rhizomatous. The areoles are usually positioned close to each other, bearing rather small, often setose spines.

The flowers are diurnal and self-sterile. They are tubular, apical, and naked, emerging from a characteristic annular cephalium. Flower colors vary from red, pink, and purple to yellow or sometimes white. Pollination is primarily ornithophilous, carried out by hummingbirds (such as Chlorostilbon lucidus, Phaethornis pretrei, and Eupetomena macroura). The fruits are spherical to pyriform, juicy, and indehiscent. Seeds are shiny, black, and tuberculate. Dispersal is essentially ornithophilous.

Habitat

The genus grows in the "caatinga", the spiny dry forest of northeastern Brazil. They are often found among bushes which serve as support for the larger species, or in the shade under shrubs. They prefer slightly loamy and sandy soils, quartz gravel, or manganesiferous altered soils, often growing alongside other Cactaceae and terrestrial bromeliads.

Altitude range: approximately 270–1100 m.

Distribution

• Brazil (Bahia, Minas Gerais, Pernambuco, Piauí)

Species

According to the Joël Lodé index, the genus currently includes the following recognized species and subspecies:

• Arrojadoa x albiflora (A. dinae x A. rhodantha)
• Arrojadoa beateae (= A. heimenii)
• Arrojadoa dinae
• Arrojadoa eriocaulis
• Arrojadoa eriocaulis subsp. nana
• Arrojadoa horstiana
• Arrojadoa marylanae
• Arrojadoa multiflora
• Arrojadoa penicillata
• Arrojadoa rhodantha
• Arrojadoa rhodantha subsp. aureispina
• Arrojadoa rhodantha subsp. reflexa

Notes

• Arrojadoa is characterized by its annular (ring-like) cephalium, from which the flowers emerge.
• Molecular analyses by Machado et al. (2006) suggest that the genus, as traditionally circumscribed, is polyphyletic.
• There is significant taxonomic discussion regarding A. marylanae; it was moved to a new genus, Arrojadoopsis, by A. Guiggi (2007) due to morphological differences, though some researchers suggest it may be a stabilized natural hybrid.
• Stephanocereus and Arrojadoa are very closely related and share the annular cephalium, but differ in pollination syndromes (chiropterophilous vs. ornithophilous) and fruit morphology.
• Some taxa previously associated with Arrojadoa have been moved to other genera based on DNA evidence, such as Micranthocereus hofackerianus.
• The genus is considered an interesting example of reticulate evolution, involving potential natural hybridizations with genera like Coleocephalocereus or Pilosocereus.