Robert S. Wallace

Phylogenetic implications of rbcL sequence variation in the Asteraceae

Complete nucleotide sequences of the rbcL gene were obtained for 25 species of Asteraceae representing 15 of the currently recognized tribes and three outgroup families. A total of 345 variable nucleotide positions was identified, 170 of which were phylogenetically informative. Phylogenetic analyses of the rbcL data generated eight equally parsimonious trees with a consistency index of 0.47. Three major monophyletic clades that correspond to the subfamilies Barnadesioideae, Cichorioideae, and Asteroideae were identified in the most parsimonious cladograms; however, support for these groups was not strong (...)

Phylogeny of the Portulacaceous Cohort Based on ndhF Sequence Data

Abstract The Portulacaceae, Basellaceae, Cactaceae, and Didiereaceae form a monophyletic group within the Caryophyllales, and evidence exists that the first may be paraphyletic if the latter three are recognized at the familial level. Several taxonomic treatments of the Portulacaceae based on morphological features have failed to produce consensus regarding infrafamilial relationships. The present paper employs sequences of the chloroplast gene ndhF to produce a molecular phylogeny of the portulacaceous cohort, focusing on the relationship among major lineages of the Portulacaceae and the three families potentially derived from within them. Results of this analysis supported two major clades within the monophyletic cohort. The first included Portulaca, Anacampseros and its relatives, much of Talinum, Talinella, and Cactaceae; the second, weakly supported, included the remaining genera of Portulacaceae, Basellaceae, and Didiereaceae. This phylogeny also showed that several generic circumscriptions remain inadequate, particularly that of Talinum sensu lato, which was polyphyletic in this analysis, and that all present classifications of the Portulacaceae include demonstrably non-monophyletic tribes. Communicating Editor: Kathleen A. Kron

Chloroplast DNA Variation in the Asteraceae: Phylogenetic and Evolutionary Implications

The sunflower family (Asteraceae) is one of the largest families of flowering plants, consisting of approximately 1,100 genera and 25,000 species (Jeffrey, 1978). The family has been variously divided into two or three subfamilies and 10 to 17 tribes (reviewed in Jansen et al., 1991a; Bremer, 1987). In addition to the disagreement concerning intrafamilial relationships, the phylogenetic affinities of the Asteraceae to other angiosperm families have been the topic of considerable debate (Cronquist, 1955,Cronquist, 1977, 1981; Carlquist, 1976; Wagenitz, 1976; Stebbins, 1977; Turner, 1977a; Jeffrey, 1977; Bremer, 1987). Until recently, systematic studies in the family relied on more traditional taxonomic characters and less rigorous phylogenetic methods. During the past five years we have been examining chloroplast DNA (cpDNA) variation in the Asteraceae to evaluate phylogenetic relationships at a wide range of taxonomic levels using several cladistic methods. We have accumulated restriction site data for approximately 250 genera in the family from all currently recognized tribes. In addition, we have sequenced the gene encoding the large subunit of ribulose-l,5-bisphosphate carboxylase (rbcL) from representative species in the Asteraceae and putatively related families. Our studies, which have produced the largest molecular data set for any plant family, have allowed us to perform phylogenetic comparisons from the intraspecific to the interfamilial levels.

Systematic Implications of Chloroplast DNA Variation in the Genus Microseris (Asteraceae: Lactuceae)

Chloroplast DNA restriction site variation was examined for all 16 species of Microseris, using 22 restriction endonucleases, filter hybridization experiments, and comparative mapping procedures. Mutations were scored relative to other genera of the subtribe Microseridinae, and related genera of the tribe Lactuceae. A total of 115 restriction site mutations was detected, 78 of which were phylogenetically informative. A single most parsimonious cladogram was constructed which indicates three major lines of evolution within the genus. The morphologically distinct annual M. lindleyi was found to be the most divergent and forms the basal lineage within the genus. Forty-three mutations separate annual and perennial species of the genus, whose average sequence divergence is 0.7%. The parentage of the allotetraploid species M. heterocarpa was confirmed, utilizing cpDNA and nuclear ribosomal DNA variation. Evaluation of relative rates of cpDNA evolution indicates that generation time is not responsible for unequal rates of cpDNA in different lineages. The results also suggest that a taxonomic reevaluation of Microseris at the subgeneric level is war- ranted. Microseris D. Don is comprised of 16 species

Phylogenetic studies of Mammillaria (Cactaceae)—insights from chloroplast sequence variation and hypothesis testing using the parametric bootstrap

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.

AN INTRON LOSS IN THE CHLOROPLAST GENE RPOC1 SUPPORTS A MONOPHYLETIC ORIGIN FOR THE SUBFAMILY CACTOIDEAE OF THE CACTACEAE

The deletion of an approximately 700-bp intron in the chloroplast-encoded generpoC1 was shown in 21 representative species of the subfamily Cactoideae of the angiosperm family Cactaceae. Members of the subfamilies Pereskioideae and Opuntioideae were found to possess the intron, as did members of the related families Aizoaceae, Basellaceae, Didiereaceae, Phytolaccaceae, and Portulacaceae. These results support a monophyletic origin for the most-speciose subfamily of the cactus family, and represent a first report of the loss of this intron in dicots.

Molecular Systematics of Tribe Cacteae (Cactaceae: Cactoideae): A Phylogeny Based on rpl16 Intron Sequence Variation

Abstract 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

Molecular Phylogenetics of the Leafy Cactus Genus Pereskia (Cactaceae)

Abstract 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 restriction-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.

Karyotypic studies in the genus Echinocereus (Cactaceae) and their taxonomic significance

SUMMARYMitotic chromosomes of 11 diploid (2n = 22) species of Echinocereus and five varieties of the polyploid (2n = 4x = 44) E. engelmannii included in the seven taxonomic sections of the genus were studied. The genus exhibits relatively symmetric karyotypes, having mostly metacentric chromosomes. Likewise, interspecific and intraspecific variability was observed in terms of genome length, chromosome length, and karyotipic formula. There was also variability in the number of satellites, and they were observed on the short arms of the chromosomes. There is an apparent correlation in decreasing chromosome and genome length in species with more derived morphological characters. In addition, karyotype asymmetry increases as the chromosome and genome length increases. Polyploid taxa investigated had larger chromosomes and genomes than diploid taxa. Robertsonian changes and centric fusion of telocentric chromosomes, are thought to be involved in the existence of homogeneous karyotypes. No evidence of structura...

Chloroplast DNA Evidence for Divergence in Ferocactus and its Relationships to North American Columnar Cacti (Cactaceae: Cactoideae)

An analysis of chloroplast DNA restriction site variation was undertaken to investigate the evolutionary divergence of Ferocactus and its possible relationship with North American columnar cacti of tribe Pachycereeae. Our chloroplast DNA study using parsimony-based phylogenetic reconstruction methods provides molecular synapomorphies to define major lineages within Ferocactus and columnar cacti of the tribe Pachycereeae. The issue of monophyly in Ferocactus remains problematic: it appears to be a paraphyletic assemblage derived from an Echinocactus-like ancestor from which three major lineages have evolved. Also, there is a lack of support for the hypothesized basal position of F flavovirens and F robustus, and no evidence was found to favor the phylogenetic relationship of Ferocactus with North American columnar cacti, in particular with Escontria chiotilla. For the columnar cacti, the study supports the monophyly of the tribe Pachycereeae as well as its two subtribes: Stenocereinae and Pachycereinae. In the Stenocereinae, Stenocerelus dumortieri was found to be in a basal position, and forms a phylogenetically distinct lineage from Stenocereus s. str. and other columnar cacti such as Escontria, Polaskia, and Myrtillocactuis. This supports the segregation of S. dumortieri from Stenocereus, and the resurrection of Isolatocereus dumortieri as a distinct genus.