Robert S Wallace’s research while affiliated with Iowa State University and other places

Members of Pereskia exhibit some presumably plesiomorphic characters for the Cactaceae including shrubby habit, non-succulent or partially succulent leaves, and in some species, nearly superior ovaries. In addition, the members show a transition from perigynous flowers with half-inferior ovaries to those species having true receptacular epigyny (the predominant condition in the Cactaceae). To examine interspecific relationships within Pereskia we utilized cpDNA restric-tion-site data and sequences from two non-coding regions of the plastid genome—the psbA-trnH intergenic spacer and the rpl16 intron. Maximum parsimony and Bayesian analyses identified three major clades: a clade containing the widespread P. aculeata and the Andean species, a clade containing six species found primarily in southeastern Brazil, Paraguay, Uruguay, Argentina, and Bolivia, and a third clade centered in southern Central America and the Caribbean. The relationship between these three clades and the rest of the Cactaceae remains unresolved, but our data do suggest that Pereskia may be paraphyletic. The sister taxon relationship for the yellow flowered species of Pereskia (P. aureiflora, P. guamacho) was also confirmed, despite their widely disjunct distribution. For many, a typical cactus is a green, leafless stem-succulent plant with numerous spines. However, mem-bers of the genus Pereskia Miller are broad-leaved trees and shrubs. They are clearly members of the cactus family due to the presence of spine-bearing areoles, a floral cup with leaf-bearing nodes, and numerous peri-anth segments. Unlike other members of the family, the ovary in Pereskia ranges from superior to fully inferior. This feature, coupled with aspects of habit, physiology, and morphology have led some researchers to con-clude that Pereskia species represent some of the most primitive members of the cacti (Gibson and Nobel 1986). Species of Pereskia are distributed throughout the northern two-thirds of South America (from northern Argentina) to Mesoamerica and the Caribbean. Back-eberg (1942) concluded that the distribution of Pereskia indicates that the genus and the cactus family arose in Mesoamerica and the Caribbean. Pereskia was first described as Peireskia by Plumier (1703) and Linnaeus (1753) used the name at species rank as Cactus pereskia. However, in the following year, Miller (1754) elevated the name to genus level in the first valid use of Pereskia at that rank. Berger (1926) believed that variation in the ovary position in Pereskia was sufficiently significant to warrant the description of subgenus Rhodocactus Berger, which was itself raised to genus level by Backeberg and Knuth (1935). The re-maining species in the genus Pereskia were divided be-tween two subgenera by Backeberg (1956), who placed the small-leaved Andean species in subgenus Neopei-reskia Backeberg. More recently, authors such as Bravo-Hollis (1978) and Leuenberger (1986) have disregarded the genus Rhodocactus, preferring to recognize a more widely circumscribed genus Pereskia. The CITES Cac-taceae Checklist (Hunt 1999) and Anderson (2001) ac-cept 17 species and two subspecies. The only recent monograph of Pereskia is that of Leuenberger (1986), in which he gives a detailed mor-phological, anatomical, and developmental account of the genus. He also presents an infrageneric treatment of the genus in which he puts forward an evolutionary and biogeographic hypothesis for the genus based upon a number of anatomical and morphological char-acters. Without being explicit, Leuenberger (1986) pre-sents seven infrageneric groups based on a small suite of morphological characters (summarized in Table 1). The lack of clear-cut synapomorphies for Pereskia sug-gest that this genus represents a grade of ''basal'' taxa, and that an exploration of variation in the genus is important to our understanding of early evolution in cacti as a whole. This paper investigates evolutionary relationships in Pereskia and informal infrageneric groupings developed by Leuenberger (1986) by devel-oping a phylogeny using a combination of sequence data from two chloroplast regions, rpl16 intron and the psbA-trnH intergenic spacer (IGS), and chloroplast DNA (cpDNA) restriction site variation.

The genus Mammillaria is likely the most species-rich and morphologically variable genus in the Cactaceae. There is doubt as to whether the genus is monophyletic, and past infrageneric treatments differ regarding generic circumscription. Phylogenetic questions about Mammillaria were addressed using chloroplast DNA sequence data from the rpl16 intron and the psbA-trnH intergenic spacer for 125 taxa (113 Mammillaria, 10 Coryphantha, Escobaria, Neolloydia, Pelecyphora, Ortegocactus, and two outgroup taxa from Ferocactus and Stenocactus). Parsimony analyses were conducted using various heuristic search strategies. Bayesian analyses were conducted using the F81 and F81 + I + G models of sequence evolution. Tree topologies from the parsimony and Bayesian analyses were largely congruent. Hypothesis testing was undertaken using the parametric bootstrap to test the monophyly of the genus and the taxonomic status of Mammillaria candida. Phylogenies derived from the parsimony and Bayesian analyses indicate that Mammillaria is not monophyletic and that the genus Mammilloydia (synonym Mammillaria) is embedded within a "core" group of Mammillaria species. Both these results were corroborated by the parametric bootstrap tests. The entire rpl16 intron was deleted from species in the Mammillaria crinita group.

Parsimony analysis of plastid rpl16 sequences from 62 members of Tribe Cacteae, and four outgroup taxa yielded 1296 equally parsimonious trees of length 666. Strict consensus evaluation of these trees established a highly pectinate topology, which delimited clades within the tribe that correspond to several previously considered generic groups. Aztekium and Geohintonia, which manifest ribs in their stem morphology were shown to represent an early divergence in the tribe, forming a sister group to remaining members of the tribe. Clades containing other genera having ribbed stems also are basal to those that develop tubercles. The most derived clade forms a distinct group of typically small stemmed species with tubercular stem morphology. Within Mammillaria, species formerly placed in the genus Cochemiea and members of the Series Ancistracanthae formed a well-supported, sister clade to the remaining members of Mammillaria. Length variation of the intron in two members of Mammillaria series Stylothelae was also observed. Communicating Editor: Thomas G. Lammers