Rhodocactus

Like all cacti, Rhodocactus species have a succulent habit and specialized structures, areoles, that bear spines. They differ from most cacti in having persistent leaves. They grow as trees, 3–7 m (10–23 ft) tall. When mature, their stems develop bark, but its development is delayed, and all the species other than Rhodocactus nemorosus retain stomata. The areoles of Rhodocactus species can form "brachyblasts",[3] called "spur shoots" by Beat Leuenberger. The areole initially forms in the axil of a leaf (stage A in the diagram below). This leaf may be lost, leaving a leaf scar, and leaves may grow on the areole (stage B). The areole may then grow out to form a brachyblast – a short, very crowded shoot that bears leaves (stage C). Later this may form a longer, but still short shoot that has its own areoles (stage D).[4] Asai and Miyata regard the formation of brachyblast leaves as a distinguishing characteristic of the genus in comparison to Pereskia.[3] Rhodocactus flowers are about 3–5 cm (1.2–2.0 in) in diameter.[3]

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  Areole and brachyblast development in Rhodocactus
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  Areole on a young stem of R. grandiflorus is in the axis of the auxoblast leaf (stage A)

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  Areoles on this stem of R. grandiflorus have brachyblast leaves (stage B)
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  Short shoot of R. grandiflorus (stage D)

Rhodocactus was originally described as a subgenus of Pereskia by Alwin Berger, and was raised to a genus in 1936 by Frederik Marcus Knuth.[1][3] The genus was later sunk back into in a broadly defined genus Pereskia. Molecular phylogenetic studies from 2005 onwards suggested that when circumscribed in this way, Pereskia was not monophyletic, and consisted of three clades.[5][6][3] By 2016, each clade was recognized as a separate genus, one of which is Rhodocactus. Only the type species of Knuth's circumscription of the genus, Rhodocactus grandifolius, belongs to the clade re-described as Rhodocactus. The other species were mostly newly transferred from Pereskia.[3]

A consensus cladogram from a 2005 study is shown below with the more recent generic assignments added. It shows that the three genera are basal to the rest of the cacti.[5]

Species

As of April 2021, Plants of the World Online accepted the following species:[2]

Image	Scientific name	Distribution
	Rhodocactus bahiensis (Gürke) I.Asai & K.Miyata<	Brazil
	Rhodocactus grandifolius (Haw.) F.M.Knuth	eastern and southern Brazil.
	Rhodocactus nemorosus (Rojas Acosta) I.Asai & K.Miyata	Brazil, Paraguay, Uruguay and northeast Argentina.
	Rhodocactus sacharosa (Griseb.) Backeb.	Bolivia and west-central Brazil to Paraguay and northern Argentina
	Rhodocactus stenanthus (F.Ritter) I.Asai & K.Miyata	Brazil

Species that have also been placed in Rhodocactus include:[3]

• Rhodocactus bleo (F.M.Knuth) F.M.Knuth = Leuenbergeria bleo F.M.Knuth) Lodé
• Rhodocactus guamacho (F.A.C.Weber) F.M.Knuth = Leuenbergeria guamacho (F.A.C.Weber) Lodé
• Rhodocactus horridus (DC.) F.M.Knuth = Pereskia horrida D.C.
• Rhodocactus lychnidiflorus (D.C.) F.M.Knuth = Leuenbergeria lychnidiflora (D.C.) Lodé
• Rhodocactus portulacifolius (L.) F.M.Knuth = Leuenbergeria portulacifolia (L.) Lodé
• Rhodocactus zinniiflorus (D.C.) F.M.Knuth = Leuenbergeria zinniiflora (D.C.) Lodé