The current understanding of the genus Stephanocereus A. Berger composed not only of Stephanocereus leucostele (Gürke) A. Berger, but also of Stephanocereus luetzelburgii (Vaupel) N. P. Taylor & Eggli (Anderson 2001; Hunt et al. 2006; Anderson & Eggli 2011; Hunt 2013), is basically due to the observation made by Eggli, that the juvenile characters of the two taxa are very similar (Taylor & Eggli 1991). Actually, the field studies relating to the morphology of the two species show more differences than similarities. In particular, while S. leucostele in its ontogenetic process can be assimilated to a "giant Arrojadoa" (evident are the common ring-like cephalia on the stem tips, a character that only rarely appears on some old individuals of S. luetzelburgii), the semaphoronts (Hennig 1966, 6-7, 32-33, 63, 65-67), globular at first, then with the characteristic elongated bottle-neck shape of S. luetzelburgii, make this taxon unique in the Cactaceae. The habitats of the two taxa are also quite distinct; while S. leucostele is characteristically found in the Bahian caatinga, S. luetzelburgii populates the campo rupestre of the Chapada Diamantina (Taylor & Zappi 2004, 290-291). This distance is also confirmed at the molecular level, where preliminary studies of gene sequences in tribe Cereeae, conducted at Kew by Patricia Soffiatti (unpubl. Data in Taylor 2002, 14: 28), show that S. luetzelburgii is separate from S. leucostele, being the first basal to a range of more derived cereoids, while the second is immediately basal to Arrojadoa Britton & Rose (represented in the analysis by A. dinae, A. rhodantha, and A. penicillata). The molecular closeness of both species of Stephanocereus to Arrojadoa is instead underlined by Machado et al. (2006), data then assimilated in this sense by Hunt (2013, xii). On the other hand, if it is true that unlike Arrojadoa pollinated by hummingbirds (ornithophily), Stephanocereus has a distinct pollination syndrome, based on nocturnal pollination by bats (chiropterophily), we recall as underlined by Taylor & Zappi (2004, 291), that A. Cardoso photographed a hummingbird while visiting the S. luetzelburgii flowers. In this regard, we also know that in Echinopsis rhodacantha (Salm-Dyck) Förster, there may be mismatches between the floral syndrome (i.e. ornithophily), and the pollinators actually observed visiting the flowers of the taxon (i.e. halictid bees, probably of the genus Dialictus) (Eggli & Giorgetta 2015, 20: 3, 8). In the same vein, molecular analysis also show that floral traits and related pollination syndromes are no longer able to distinguish taxa at a generic level (Ritz et al. 2007; Lendel et al. umpubl. data & Nyffeler et al. umpubl. data in Nyffeler & Eggli 2010; Schlumpberger & Renner 2012; Anceschi & Magli 2013a; 2013b). That said, on the basis of morphological and molecular data in our possession, we prefer to distinguish the truly exceptional form of Stephanocereus luetzelburgii in the monotypic genus Lagenosocereus Doweld, as Lagenosocereus luetzelburgii (Vaupel) Doweld, and instead include S. leucostele among the members of Arrojadoa as Arrojadoa leucostele (Gürke) Anceschi & Magli (for the latter see on p. 39 of the present booklet). (Quoted from Anceschi & Magli 2021, 72-73)
July 2021