Salvador Arias

Comparative Stem Anatomy in the Subfamily Cactoideae

Basic anatomical features of Cactaceae have been studied since the sixteenth century. This anatomical research has focused on selected features related to different external forms or on stem photosynthetic metabolism. Anatomical stem features, however, have rarely been taken into consideration in systematic studies. Recent work has focused on the subfamily Cactoideae because it is the largest and most diverse subfamily of Cactaceae. Molecular analyses support the monophyly of Cactoideae, but tribal and generic relationships are mostly unresolved. A major goal of this study was to synthesize the available information about anatomical stem features of Cactoideae and to evaluate their usefulness in phylogenetic analysis. Although dermal and vascular tissues have been studied for nearly 350 species of Cactoideae, comprehensive investigations are needed for most members of specific genera or tribes. Phylogenetic analysis based on structural data (morphology and anatomy) showed that the subfamily Cactoideae is monophyletic. This result supports molecular evidence and corroborates that highly reduced leaves are the synapomorphy of this clade. With the exception of Cacteae and Rhipsalideae, the tribes are not monophyletic. The morphological characters that have been used to define the tribes are not synapomorphies and have evolved independently in different lineages. Some anatomical features are unique characters that distinguish terminal taxa; for example, silica grains in dermal and hypodermal cells inStenocereus, prismatic crystals in dermal and hypodermal cells ofNeobuxbaumia, and lack of medullary bundles in members of Cacteae. Most anatomical features, however, behave in a highly homoplasious manner in the analysis of the subfamily. Other studies at the tribal or generic level show that anatomical features are informative and contribute to support different clades. Further studies of Cactoideae, at different taxonomic levels, that include anatomical features, are needed in order to understand their evolution.ResumenDesde el siglo dieciseis se inició el estudio los caracteres anatómicos en Cactaceae. La investigación se ha enfocado a caracteres relacionados con las diferentes formas y el metabolismo fotosintético de los tallos. Sin embargo, en pocos estudios las estructuras anatómicas se han empleado en la sistemática de la familia. La investigación se ha centrado en la subfamilia Cactoideae porque es la más grande y diversa dentro de Cactaceae. Estudios moleculares apoyan la monofilia de Cactoideae; sin embargo, las relaciones tribales y genéricas son inciertas. Uno de los objetivos de este trabajo fue sintetizar la información sobre los caracteres anatómicos del tallo en Cactoideae y evaluarla desde una perspectiva filogenética. Aunque se ha estudiado el tejido dérmico o vascular de alrededor de 350 especies de Cactoideae, se requieren estudios que incluyan a la mayoría de las especies de géneros y tribus específicos. El análisis filogenético basado en datos estructurales (morfología y anatomia) mostró que la subfamilia Cactoideae es monofilética. Este resultado apoya las evidencias moleculares y corrobora que las hojas altamente reducidas son la sinapomorfia de este clado. Excepta por las tribus Cacteae y Rhipsalideae, las otras tribus no se recuperaron como monofiléticas. Los caracteres morfológicos que se han empleado para circunscribir las tribus no son sinapomorfias y se han adquirido en forma independiente en varios linajes. Varios caracteres anatómicos son únicos y distinguen a algunos taxa terminales como son la presencia de cuerpos de sílice en la epidermis e hipodermis deStenocereus, los cristales prismáticos en la epidermis e hipodermis deNeobuxbaumia y la ausencia de haces medulares en especies de Cacteae. Sin embargo, la mayoría de los caracteres anatómicos son homoplásicos en el análisis de la subfamilia, pero otros estudios a nivel tribal o genérico han mostrado que son informativos y contribuyen a diferenciar clados. Existe la necesidad de un mayor número de estudios a diferentes niveles taxonómicos que incluyan características anatómicas con la finalidad entender su evolución.

Phylogenetic Analysis of Pachycereus (Cactaceae, Pachycereeae) based on Chloroplast and Nuclear DNA Sequences

Abstract The phylogenetic relationships of Pachycereus (Cactaceae) species and relatives from subtribe Pachycereinae were studied using DNA sequence data. The plastid rpl16 intron, trnL intron, trnL-F intergenic spacer, and nuclear rDNA internal transcribed spacer region (ITS) were sequenced for 30 species, representing the four genera of subtribe Pachycereinae (Carnegiea, Cephalocereus, Neobuxbaumia, and Pachycereus) as well as three additional outgroup genera from subtribe Stenocereinae. Phylogenetic analyses support neither the monophyly of Pachycereus as currently circumscribed nor Pachycereinae unless Stenocereus aragonii and S. eichlamii are included within it. However, these results suggest that the subtribe can be divided into three major clades. The first includes Pachycereus hollianus and P. lepidanthus, which is sister to a large clade combining species from the Pachycereus and Cephalocereus groups. Within this large clade Cephalocereus and Neobuxbaumia together with Pachycereus fulviceps are sister to the remaining species of Pachycereus as well as Stenocereus aragonii, S. eichlamii, and Carnegiea gigantea. Our results suggest that Pachycereus is paraphyletic and that several other genera (Backebergia, Lemaireocereus, Lophocereus, and Pseudomitrocereus) may be resurrected to accommodate these new phylogenetic insights. A number of morphological and anatomical characters support these relationships, indicating that future analyses combining both molecular and morphological characters will be particularly useful in resolving relationships within this group of columnar cacti.

Phylogenetic relationships in Peniocereus (Cactaceae) inferred from plastid DNA sequence data

The phylogenetic relationships of Peniocereus (Cactaceae) species were studied using parsimony analyses of DNA sequence data. The plastid rpl16 and trnL-F regions were sequenced for 98 taxa including 17 species of Peniocereus, representatives from all genera of tribe Pachycereeae, four genera of tribe Hylocereeae, as well as from three additional outgroup genera of tribes Calymmantheae, Notocacteae, and Trichocereeae. Phylogenetic analyses support neither the monophyly of Peniocereus as currently circumscribed, nor the monophyly of tribe Pachycereeae since species of Peniocereus subgenus Pseudoacanthocereus are embedded within tribe Hylocereeae. Furthermore, these results show that the eight species of Peniocereus subgenus Peniocereus (Peniocereus sensu stricto) form a well-supported clade within subtribe Pachycereinae; P. serpentinus is also a member of this subtribe, but is sister to Bergerocactus. Moreover, Nyctocereus should be resurrected as a monotypic genus. Species of Peniocereus subgenus Pseudoacanthocereus are positioned among species of Acanthocereus within tribe Hylocereeae, indicating that they may be better classified within that genus. A number of morphological and anatomical characters, especially related to the presence or absence of dimorphic branches, are discussed to support these relationships.

Molecular phylogeny, origin and taxonomic implications of the tribe Cacteae (Cactaceae)

This study aimed to test the phylogenetic relationships of the tribe Cacteae, the generic circumscription within the tribe, in particular, the monophyly of the genus Ferocactus, and to provide a biogeographical hypothesis about the origin of Cacteae. The analysis included 135 species from all of the 27 accepted genera and four outgroup species. Five chloroplast regions were sequenced, aligned, and coded postulating gaps, simple sequence repeats (SSRs), and inversions as potential synapomorphies, and their contributions to phylogenetic reconstruction were evaluated. The phylogenetic analyses recovered 63% of the genera as monophyletic. The contribution of rpl16, trnL-F and psbA to the phylogenetic signal was higher than in the two more slowly evolving genes (rbcL, matK), but the gaps and SSRs supported some of the genera. This result differs from those of previous phylogenetic studies in which less than 35% of the genera were recovered as monophyletic. In this work, Astrophytum and Echinocactus were re-circumscribed with five and four species, respectively. Turbinicarpus was found to be polyphyletic; 11 species correspond to Turbinicarpus s.str., whereas a highly supported clade corresponded to Rapicactus, and three species need further study. Contrary to its current circumscription, Ferocactus was not supported as monophyletic because it is polyphyletic concerning Glandulicactus, Leuchtenbergia, Stenocactus and Thelocactus. We recognize this group of genera as the Ferocactus clade in which the species share the presence of scales in the pericarpel and ribbed stems, whether tuberculated or not. The Cacteae seem to have originated in the Sierra Madre Oriental and then dispersed to the Mexican Plateau, where radiation and diversification occurred at the boundaries of the Miocene–Pliocene Epoch. The development of the Mexican Plateau and the Trans-Mexican Volcanic Belt may have favoured the isolation of the Cacteae. A taxonomic diagnosis is presented for the tribe Cacteae and 18 genera that we now recognize.

El hábito y la forma de crecimiento en la tribu Cacteae (Cactaceae, Cactoideae)

The terms ‘growth form’ and ‘habit’ are often used as synonyms. However, their assignment to different species is problematic because of the morphological diversity occurring in some taxonomic groups, as is the case in Cactaceae, particularly in the tribe Cacteae of the Cactoideae subfamily. Stem morphology was studied in 102 species (26 genera) of Cacteae in order to identify the habit and to recognize how many growth forms occur in the tribe, as well to make a distinction between the concepts of habit and growth form in Cactaceae, and to discuss the differences between them and the concepts of life form and plant architecture. Based on observations and measurements for 102 species of Cacteae, four growth forms (cylindrical, columnar, globose, and globose-depressed) were recognized. Neither the habit ‘tree’ or ‘herb’ can be assigned to any member of Cacteae based on their size or longevity. Twelve percent of the studied species of this tribe have basitonic branching (shrubs) as for Acharagma roseana, Ferocactus pilosus and Thelocactus bicolor . In order to avoid confusion, we suggest using only the term ‘growth form’ when referring to the various stem forms in the Cacteae tribe.

Morphology and anatomy of the Cephalocereus columna-trajani cephalium: why tilting?

The morphology and anatomy of the Cephalocereus columna-trajani flowering region was described and compared with data on other species. The vegetative and reproductive regions were described in detail. The results showed that after the flowering region is differentiated, morphological changes take place which are correlated with anatomical changes. The flowering region in this species is termed a lateral cephalium because of its reduced interareolar space, increased areole size and abundant long bristles and trichomes in the areoles. Periderm development near the apical meristem, lack of chlorenchyma and a delay in xylem fiber differentiation are also traits characteristic of a lateral cephalium. The lateral cephalium of C. columna-trajani shared the same combination of morpho-anatomical characters with its sister taxon, C. senilis, except for the number of ribs in the cephalium. Both species survive in high temperature environments and their cephalium faces north; however, only C. columna-trajani tilts, thus we hypothesize that incorporation of fewer ribs associated with periderm development in the cephalium contributes to stem tilting.

Análisis cladístico del género Pachycereus (Cactaceae) con caracteres morfológicos

ResumenEl géneroPachycereus incluye 13 especies de acuerdo con las clasificaciones más recientes, y se distribuye en Guatemala, México y SW de los Estados Unidos, Se presenta un análisis filogenético con el propósito de fundamentar la monofilia del género, respecto a los otros géneros de la subtribu Pachycereinae. Se creó una matriz utilizando 44 caracteres estructurales (morfología y anatomía) y 29 taxones, incluyendo nueve especies de Pachycereinae. Los resultados indican que la subtribu Pachycereinae sólo puede ser monofilética si se incluyen dos especies deStenocereus: S. aragonii y.S. eichlamii, con base en dos caracteres de la semilla (paredes periclinales planas y microrrelieve finamente rugoso). El géneroPachycereus no es monofilético de acuerdo con la clasificación más reciente;Pachycereus hollianus yP. lepidanthus carecen de zona fértil diferenciada y representan el grupo hermano de las restantes especies de la subtribu Pachycereinae;P. fulviceps está relacionado con los génerosCephalocereus yNeobuxbaumia por el tipo de zona nectarial, el color de la pulpa del fruto y los cristales prismáticos de oxalato de calcio en células epidérmicas;P. grandis, P. pecten-aboriginum, P. pringlei, P. tepamo yP. weberi se resuelven como grupo monofilético por presentar un surco angosto y una flor con constricción en la base del tubo. Este grupo de cinco especies debe representar al géneroPachycereus sensu stricto.AbstractThe genusPachycereus is restricted to Guatemala, Mexico, and the SW United States and includes 13 species according to the most recent classification. A phylogenetic analysis was conducted in order to test the monophyly ofPachycereus with respect to other genera of subtribe Pachycereinac. A matrix of 44 structural characters (morphology and anatomy) was scored for 29 taxa, including nine species of the Pachycereinae. Results obtained indicated that the subtribe Pachycereinae can only be monophyletic if two species ofStenocereus (S. aragonii andS. eichlamii) are included in it, based on two seed characters (smooth periclinal wall and finely rough relief).Pachycereus is not monophyletic according to the most recent classification.Pachycereus hollianus andP. lepidanthus lack a differentiated fertile zone, and form a basal group in the subtribe Pachycereinae; they do not belong to the genusPachycereus. Pachycereus fulviceps is related to the generaCephalocereus andNeobuxbaumia based on nectar zone type, color of fruit pulp. and prismatic calcium oxalate crystals in the epidermic cells.Pachycereus grandis. P. pecten-aboriginum, P. pringlei, P. tepamo, andP. weberi are a monophyletic group, based on the presence of a narrow interareolar groove and flowers with a basally constricted tube. This group of five species comprises the genusPachycereus sensu stricto.

The systematic significance of seed morphology in Stenocereus (Cactaceae)

Seed morphology of 24 species of Stenocereus was examined by scanning electron microscopy. Quantitative and qualitative features were evaluated to identify groups of species using a phenetic analysis. Two groups were distinguished based on morphological variations of seed size, luster, multicellular sculpture, keeling, cell-size, periclinal wall sculpture, microrelief and HM complex shape and position relative to rim. All species studied were keeled, with isodiametric cells in the lateral region. Stenocereus alamosensis, S. kerberi and S. beneckei are unique among Stenocereus species in that their seeds are flat but lack micro-relief. Stenocereus aragonii and S. eichlamii have large, glossy seeds lacking micro-relief unlike other Stenocereus species, but like most Pachycereus, are unique in that cells in the lateral region display partly convex, low domes. Quantitative and qualitative congruence and discordance among characters that determine species groups in Stenocereus are discussed.

Taxonomic Revision of Pachycereus (Cactaceae)

Abstract A comprehensive taxonomic revision of the genus Pachycereus (Cactaceae, Cactoideae, Pachycereeae) is presented. Pachycereus is characterized by one synapomorphic character, the presence of a narrow interareolar groove, and by the combination of flowering region differentiated with flexible spines, flower with a narrow region between the pericarpel and the receptacular tube and the occurrence of trichomes and short spines in the pericarpel. Five species are recognized in the present treatment. One species (P. pecten-aboriginum) is widely distributed from Chihuahua in northern Mexico to Chiapas, three species (P. grandis, P. pringlei, and P. weberi) are restricted to defined floristic provinces, and one species (P. tepamo) is endemic to Depresion del Balsas. A key and descriptions of the species, based on herbarium specimens, field observations and intensive field collection are presented. The taxonomic history, synonymies, distribution, uses, and representative specimens are included. Three new combinations, Pterocereus gaumeri subsp. foetidus, Lemaireocereus lepidanthus, and Lophocereus marginatus, are proposed.

Phylogenetic Relationships in Echinocereus (Cactaceae, Cactoideae)

Abstract Echinocereus is the third most species-rich genus in the Cactaceae. It is distributed in North America from Mexico to the central U. S. A. Previous molecular phylogenetic studies have indicated that the genus is polyphyletic, but incomplete taxon sampling and unclear resolution have hindered the formal re-evaluation of generic and infrageneric circumscriptions. To address this problem, we analyzed six plastid regions (matK, rbcL, psbA-trnH, trnQ-rps16, rpl16, and trnL-F) using maximum parsimony and Bayesian inference criteria for 59 species, including all previously proposed infrageneric entities and representing the full range of morphological variation known in the genus. Our results support the monophyly of Echinocereus if E. pensilis is excluded and reestablished as the monotypic genus Morangaya. Two additional morphological characters, erumpent flower buds and green stigma lobes, further support the circumscription of Echinocereus sensu stricto. Phylogenetic analyses recovered nine main clades in Echinocereus s. s., one of which corresponds to the Triglochidiati section; the remaining clades did not correspond to any other recognized sections. We suggest a re-evaluation of previously proposed infrageneric entities.