Monserrat Vázquez-Sánchez

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.

Stem and wood allometric relationships in Cacteae (Cactaceae)

Allometric relationships in organisms are considered a universal phenomenon. A positive scaling has been reported between stem size and cellular size of tracheary elements in wood of different vascular plants, but few studies have been carried out in slow-growing succulent plants. The aim of this study was to evaluate if a relationship exists between size, growth form and wood cell size among individual species of Cacteae. Forty-four species belonging to 16 genera of the tribe Cacteae with differing growth forms and sizes were studied. When analyzing plant size, we found a positive allometric scaling and the larger-sized species showing a higher percentage of succulent tissue and less accumulation of wood tissue. The positive scaling found between plant size (height and diameter) and vessel elements and fiber length support the universality of the allometric relationship proposed for other vascular plants with non-succulent stems. Notably, wide-band tracheids do not scale with plant size or growth form. Succulence associated with narrow vessel elements with distinctive helical secondary walls and wide-band tracheids suggest they are the key adaptations to tolerate drought and provide support to the stems of most taxa in Cacteae. Fibers do not have the primary role of giving mechanical support; therefore, we assume the scarce fibers in clusters represent reaction wood that, along with the fundamental tissue, maintains the vertical position and shape of those species growing in rocky cracks. Our results with species having short succulent stems support the universal theory of positive allometric scaling of vascular plants.

Growth form and wood evolution in the tribe Cacteae (Cactaceae)

Abstract: Using the phylogeny of the tribe Cacteae as a model, we describe and trace the structural traits of its 135 taxa with the goal of reconstructing the growth form and wood evolution within the tribe. The reconstruction of growth form, podaria arrangement, wood, dilated rays, hypodermis cells, cortex and pith was performed using the parsimony method implemented in Mesquite. Although there is a high level of homoplasy, we speculate that many of the anatomical modifications are related to stem biomechanics, while others are adaptations to environmental changes that occurred during the diversification of the tribe during the Miocene period. The different combinations of morphological (podaria) and anatomical characters (dimorphic wood and lignification of the fundamental tissue) favour the maintenance of the growth form by avoiding stem deformation during long drought periods. Citation: Vázquez-Sánchez M., Terrazas T., Grego-Valencia D. & Arias S. 2017: Growth form and wood evolution in the tribe Cacteae (Cactaceae). — Willdenowia 47: 49–67. doi: https://doi.org/10.3372/wi.47.47106 Version of record first published online on 14 March 2017 ahead of inclusion in April 2017 issue.

Comparative morphology and anatomy of Backebergia militaris (Echinocereeae–Cactaceae) cephalium

The morphology and anatomy of the Backebergia militaris cephalium is characterized in comparison with its vegetative branch and with apical and lateral cephalia of other species. Our working hypothesis was that the B. militaris cephalium is more similar to the apical or lateral cephalia of other taxa than to its own vegetative branch. Our results revealed that the differences between the vegetative branch and the cephalium are primarily morphological: there is a change in the phyllotaxy, there are no interareolar spaces, making the ribs indistinguishable and abundant trichomes and bristles are produced in the areoles. In addition, a comparison between the vegetative branch and the cephalium shows differences in the epidermal cell size, thickness of the hypodermis and abundance of cortical bundles and mucilage cells. Unlike Melocactus intortus apical cephalia, B. militaris retains stomata in the epidermis and chlorenchyma, allowing the cephalium near the apical meristem to perform photosynthesis. The development of periderm in each areole after flowering and fruiting is a distinctive and defining feature of lateral and apical cephalia. In addition to early periderm development, the necrosis of cortical and pith parenchyma and fibers in secondary xylem and phloem in B. militaris distinguishes it from other cephalia described to date.

Ferocactus (Cactaceae) epidermis: its systematic value1

Abstract The stem epidermis of 23 species and three subspecies of Ferocactus Britton & Rose from the tribe Cacteae-Cactaceae are described and compared using scanning electron and light microscopy. Epidermal-hypodermal samples were removed, prepared for observation, and analyzed using a similarity method. Our observations showed that most epidermal cells had an elongate-tetragonal outline with straight anticlinal walls. However, S and U-undulated anticlinal walls occurred in F. glaucescens (DC.) Britton & Rose and F. peninsulae (Engelm. ex F.A.C. Weber) Britton & Rose (Cactaceae). The microrelief of the anticlines was flat and inconspicuous or striate. The periclinal wall relief varied from none to rugose or verrucose among species; 89% of the studied species had slightly sunken or sunken parallelocytic stomata with 2 or 3 pairs of subsidiary cells. Cuticle thickness varied from 2.54 µm in F. histrix (DC.) G.E. Linds to 39.74 µm in F. flavovirens (Scheidw.) Britton & Rose and their thickness is not related to environment. Silica bodies in the hypodermis cell lumina are present in 90% of the species studied. The epidermal characters of the Ferocactus species have been described in other members of Cactoideae, none of them can be postulated as possible synapomorphies to the genus level. Pustules, which are a cutin accumulations on the outer epidermal walls are distinctive feature of F. emoryi (Engelm.) Orcutt, and here are described for the first time for the Cactaceae. The phenogram revealed three groups, and F. haematacanthus (Salm-Dyck) Bravo was revealed as the most distinct species within the genus as well as F. histrix. Both were the early derived species in the most recent phylogeny. A combination of epidermal characters can help to distinguish some Ferocactus species, but failed to support the infrageneric classifications. However, some groups of species based on their epidermal similarities agree with some clades in the most recent phylogeny.