Subfamily Cactoideae Research Articles

Association between cacti and nurse plants: a quantitative literature review

The association between cacti and nurse plants has been reviewed by different authors. These reviews however were qualitative because only evaluated aspects such as species identity of cacti and nurse plants, probable explanatory causes of their association, and location of study sites. To our knowledge, there are no quantitative reviews that have evaluated the association between cacti and nurse plants for different subfamilies, tribes, and growth forms of cacti and nurse plants, and different plant communities and soil properties. To address these issues, we performed a quantitative review of the studies on the association between cacti and nurse plants. The studies were searched in the ISI Web of Knowledge from 1986 to 2021. Data obtained from studies were analyzed with the relative risk ratio and ratio of medians. Most studies on the association between cacti and nurse plants were performed mainly in Mexico and the USA. Globose, cylindrical, and columnar cacti of the subfamily Cactoideae, and tribes Cacteae, Cereeae, and Echinocereeae were associated to nurse plants of Asteraceae, Euphorbiaceae, and Fabaceae. However, other subfamilies (Opuntioideae) and tribes (Notocacteae) of cacti, and families (Asparagaceae) of nurse plants were not associated. Nurse plants ameliorated temperature, moisture, and nitrogen of soil. The association between cacti and nurse plants occurred in desert shrubland and tropical dry forest. Further studies are needed on the association between cacti and nurse plants that consider more cactus subfamilies and tribes in countries with high cactus diversity in Central and South America.

Cytogenetic Characteristics of Four Gymnocalycium (Cactaceae) Species along Altitudinal Gradients

Species can have broad altitudinal distributions and their characteristics may vary throughout distribution ranges. Ploidy level can vary along environmental gradients, such as altitudinal ones. However, the relationships between ploidy level and altitude may be diverse. The karyotype allows us to know the structural and quantitative characteristics of the chromosomal pairs and to relate these characteristics to the environment where the species occur. Species of the Cactaceae family can be found from sea level to 4500 m above sea level (asl). The greatest species richness is found in mountain areas, where species occupy wide altitudinal ranges. Gymnocalycium belongs to the subfamily Cactoideae; it is a genus endemic to southern South America and its main center of diversity is found in the mountain ranges of central and northern Argentina. The basic chromosome number for Cactaceae is x = 11, with polyploidy being the main existing variation. The aim of this work was to analyze cytogenetic variables in populations of four species of the genus Gymnocalycium (G. andreae, G. erinaceum, G. monvillei, and G. mostii) along their altitudinal distribution. Idiograms were constructed using HCl/Giemsa, CMA/DAPI fluorescent chromosomal banding and fluorescent in situ hybridization (FISH). The karyotypes of the analyzed populations of each species were symmetric and showed little variation in size and symmetry. All the populations of G. andreae, G. erinaceum and G. mostii were found to be diploid and had the greatest distribution; G. monvillei was found to be tetraploid in all the populations analyzed. CMA+/DAPIbands associated with secondary constrictions (NORs) were detected in all the populations of all the species. The cytogenetic characteristics of the studied species were constant along the altitudinal gradients, showing that they can occur at different altitudes without major cytogenetic modifications.

A target Capture Probe Set Useful for Deep- and Shallow-Level Phylogenetic Studies in Cactaceae.

The molecular phylogenies of Cactaceae have enabled us to better understand their systematics, biogeography, and diversification ages. However, most of the phylogenetic relationships within Cactaceae major groups remain unclear, largely due to the lack of an appropriate set of molecular markers to resolve its contentious relationships. Here, we explored the genome and transcriptome assemblies available for Cactaceae and identified putative orthologous regions shared among lineages of the subfamily Cactoideae. Then we developed a probe set, named Cactaceae591, targeting both coding and noncoding nuclear regions for representatives from the subfamilies Pereskioideae, Opuntioideae, and Cactoideae. We also sampled inter- and intraspecific variation to evaluate the potential of this panel to be used in phylogeographic studies. We retrieved on average of 547 orthologous regions per sample. Targeting noncoding nuclear regions showed to be crucial to resolving inter- and intraspecific relationships. Cactaceae591 covers 13 orthologous genes shared with the Angiosperms353 kit and two plastid regions largely used in Cactaceae studies, enabling the phylogenies generated by our panel to be integrated with angiosperm and Cactaceae phylogenies, using these sequences. We highlighted the importance of using coalescent-based species tree approaches on the Cactaceae591 dataset to infer accurate phylogenetic trees in the presence of extensive incomplete lineage sorting in this family.

The plastome of Melocactus glaucescens Buining & Brederoo reveals unique evolutionary features and loss of essential tRNA genes.

The plastome of Melocactus glaucescens shows unique rearrangements, IR expansion, and unprecedented gene losses in Cactaceae. Our data indicate tRNA import from the cytosol to the plastids in this species. Cactaceae represents one of the richest families in keystone species of arid and semiarid biomes. This family shows various specific features comprehending morphology, anatomy, and metabolism, which allow them to grow under unfavorable environmental conditions. The subfamily Cactoideae contains the most divergence of species, which are highly variable in growth habit and morphology. This subfamily includes the endangered species Melocactus glaucescens (tribe Cereeae), which is a cactus endemic to the biome Caatinga in Brazil. Aiming to analyze the plastid evolution and develop molecular markers, we sequenced and analyzed in detail the plastome of M. glaucescens. Our analyses revealed that the M. glaucescens plastome is the most divergent among the species of the family Cactaceae sequenced so far. We characterized here unique rearrangements, expanded IRs containing an unusual set of genes, and several gene losses. Some genes related to the ndh complex were lost during the plastome evolution, while others have lost their functionality. Additionally, the loss of three tRNA genes (trnA-UGC, trnV-UAC, and trnV-GAC) suggests tRNA import from the cytosol to the plastids in M. glaucescens. Moreover, we identified high gene divergence, several putative positive signatures, and possible unique RNA-editing sites. Furthermore, we mapped 169 SSRs in the plastome of M. glaucescens, which are helpful to access the genetic diversity of natural populations and conservation strategies. Finally, our data provide new insights into the evolution of plastids in Cactaceae, which is an outstanding lineage adapted to extreme environmental conditions and a notorious example of the atypical evolution of plastomes.

Genetic and evolutionary analyses of plastomes of the subfamily Cactoideae (Cactaceae) indicate relaxed protein biosynthesis and tRNA import from cytosol

Cactaceae arose ca. 30–35 million years ago (Mya) and comprises keystone species of arid and semiarid biomes. Various specific features related to morphology, anatomy, and CAM metabolism have likely favored diversification and expansion under arid environments. The plastome of most cactus species also undergone several evolutionary features to adapt growth and development under adverse environmental conditions. Aiming to enhance the understanding of the plastid evolution in the subfamily Cactoideae, we sequenced and analyzed in detail the plastome of Rhipsalis teres (Vell.) Steud., an epiphytic species from the Atlantic forest. The plastome of R. teres contains the two main rearrangements found in other plastomes of the subfamily Cactoideae. Our structural analyses suggested that the ancestral plastome architecture served as the basic structure for homologous recombination-mediated diversification of the IR boundaries found in them. Cactoideae plastomes show several polymorphic RNA editing sites, which are mainly distributed in genes related to gene expression machinery. Interestingly, the loss of rpl33 and rpl36 genes suggests a relaxed plastid biosynthesis in these species. Also, the absence of the trnV-UAC gene indicates the emergence of a tRNA import mechanism given that, for steric reasons, all valine codons cannot be read by the tRNAVal(GAC). Finally, our data indicate that the environment imposed several evolutionary features in the plastomes of Cactoideae during evolution under arid and semiarid biomes allowing adaptation and diversification.

Insights Into Chloroplast Genome Evolution Across Opuntioideae (Cactaceae) Reveals Robust Yet Sometimes Conflicting Phylogenetic Topologies.

Chloroplast genomes (plastomes) are frequently treated as highly conserved among land plants. However, many lineages of vascular plants have experienced extensive structural rearrangements, including inversions and modifications to the size and content of genes. Cacti are one of these lineages, containing the smallest plastome known for an obligately photosynthetic angiosperm, including the loss of one copy of the inverted repeat (∼25 kb) and the ndh gene suite, but only a few cacti from the subfamily Cactoideae have been sufficiently characterized. Here, we investigated the variation of plastome sequences across the second-major lineage of the Cactaceae, the subfamily Opuntioideae, to address (1) how variable is the content and arrangement of chloroplast genome sequences across the subfamily, and (2) how phylogenetically informative are the plastome sequences for resolving major relationships among the clades of Opuntioideae. Our de novo assembly of the Opuntia quimilo plastome recovered an organelle of 150,347 bp in length with both copies of the inverted repeat and the presence of all the ndh gene suite. An expansion of the large single copy unit and a reduction of the small single copy unit was observed, including translocations and inversion of genes, as well as the putative pseudogenization of some loci. Comparative analyses among all clades within Opuntioideae suggested that plastome structure and content vary across taxa of this subfamily, with putative independent losses of the ndh gene suite and pseudogenization of genes across disparate lineages, further demonstrating the dynamic nature of plastomes in Cactaceae. Our plastome dataset was robust in resolving three tribes with high support within Opuntioideae: Cylindropuntieae, Tephrocacteae and Opuntieae. However, conflicting topologies were recovered among major clades when exploring different assemblies of markers. A plastome-wide survey for highly informative phylogenetic markers revealed previously unused regions for future use in Sanger-based studies, presenting a valuable dataset with primers designed for continued evolutionary studies across Cactaceae. These results bring new insights into the evolution of plastomes in cacti, suggesting that further analyses should be carried out to address how ecological drivers, physiological constraints and morphological traits of cacti may be related with the common rearrangements in plastomes that have been reported across the family.

Karyotype characterization and evolution of chromosome number in Cactaceae with special emphasis on subfamily Cactoideae

ABSTRACT Cactaceae species are karyotypically well-known with x = 11 and chromosome number variation due mainly to polyploidization. However, both assumptions are based on descriptive observations without taking an evolutionary framework of Cactaceae into account. Aiming to confirm these hypotheses in an evolutionary context, we obtained chromosome numbers for 20 species of Cactoideae, performed an extensive review of chromosome number for the family, and analyzed these data using a phylogenetic approach. The karyotypes presented here were characterized by CMA/DAPI banding, and for six species 5S and 45S rDNA sites were located. Our data, along with a survey of the literature, reinforce the long-standing hypothesis of a x = 11 as the base chromosome number for Cactaceae. They also reinforce the relevance of polyploidy in karyotype evolution of cacti, although polyploidy was important just after the diversification of subfamilies Maihuenioideae and Pereskioideae. Despite the homogeneous chromosome complements observed among cacti, chromosome banding and FISH techniques revealed informative characteristics, allowing the identification of chromosome synapomorphies, such as proximal CMA+ bands in Melocactus and proximal 5S rDNA in Pilosocereus, indicating the taxonomic potential of chromosome characterization in cacti.

Damage in Cactaceae, their geographic distribution and new evidences

Background: Field observations of damage in columnar cacti of central Mexico, and previous evidence in scientific literature, indicated the absence of systematic information about kinds of damage, vectors, and pathogens, in this botanical family.
 Questions: How is the knowledge of damage and defense mechanisms in cacti? Is there a pattern in causal agents and their geographical distribution in the Americas?
 Methods: A database of 58 taxa by 51 types of damage was developed from literature recorded in ISI Web of Knowledge, Cabdirect, and Google Scholar, and it was analyzed by multivariate methods.
 Results: From 1,500 species of Cactaceae, only 58 have been studied through this scope. Subfamily Cactoideae has been the most studied, in particular tribe Echinocereeae (= Pachycereeae columnar cacti). Multivariate analysis grouped cacti according to the kind of damage: biotic, or abiotic. Damage due to biotic factors was sub-grouped depending on the herbivores. Damage by abiotic factors is more frequent in extreme latitudes. Fourteen species of columnar cacti were reported with herbivory and rot damage in Central Mexico, of which eight represent new records of damaged cacti. 
 Conclusions: The evidence from field observations, and few recent publications suggest that some generalist herbivores are becoming dangerous in this region, Future research is necessary in order to understand the dynamics of the dispersion of some kinds of damage, the role of human disturbance, and the role and changes in defense mechanisms in wild and domesticated cacti.

Systematic relevance of pollen morphology in tribe Hylocereeae (Cactaceae).

Hylocereeae is one of the nine tribes in the subfamily Cactoideae (Cactaceae), for which the limits and recognition of genera have been controversial. Essentially, this group comprises epiphytic and hemiepiphytic genera with stems modified as climbing structures. The aim of this paper is to examine pollen attributes in representative species of genera of Hylocereeae, focusing on Selenicereus whose current circumscription comprises Hylocereus and three Weberocereus species, to find whether significant potentially apomorphic and/or autapomorphic systematic characters can be discovered. Utilizing SEM and light microscopy, 25 pollen characters were observed and measured. Tribe Hylocereeae is stenopalynous, with pollen grains isopolar and radially symmetrical monads, mostly tricolpate, except in Kimnachia, Pseudoripsalis and Weberocereus, whose pollen grains are pantocolpate. Seven attributes (five qualitative and two continuous) exhibited useful variation and were coded. The character of brevicolpate pollen grains was shared by Kimnachia ramulosa and Pseudorhipsalis amazonica. Convex quadrangular outline in the polar view was shared by Weberocereus tunilla and S. glaber. The absence of spinules on the exine was shared by S. minutiflorus and S. stenopterus. The largest pollen grain, found in Selenicereus megalanthus, might be correlated with polyploidy. Selenicereus is the taxon with the highest variation in pollen attributes, including species with an exine with or without spinules and variable polar area index and shape (subprolate or oblate-spheroidal).

Many Cacti Have Clusters of Terminal Tracheids on Their Cortical Bundles

Most cacti in subfamily Cactoideae have a thick cortex vascularized by a network of cortical bundles. It was noticed that some cortical bundles had a leaf-like feature: clusters of terminal tracheids. The objective of this research was to examine a range of species and characterize the clusters. Of the 226 species examined in 85 genera, 105 (46.7%) had clusters of terminal tracheids. Species with clusters were widely distributed throughout the subfamily. A few genera were uniform, with all sampled species having clusters (Ariocarpus, Corryocactus) or with all sampled species lacking them (Armatocereus, Mammillaria, Melocactus). Most genera were variable (e. g., Cereus, Cleistocactus) having some species with terminal tracheid clusters and other species lacking them. Where present, the clusters consisted of short, broad tracheids (not vessel elements), one or several phloem poles, but never fibers or sclereids (except Strombocactus disciformis). Clusters were most likely to occur at the apex of a rib or tubercle, especially near an areole; they often also occurred along the face of a rib; they were least common at the sinuses between ribs. Without exception, they occurred within the palisade cortex or along its base but never deep within the cortex. No ecological or functional role was obvious.

Anatomical and morphological features of seedlings of some Cactoideae Eaton (Cactaceae Juss.) species

<p>Three-month-old seedlings of 11 species of the subfamily Cactoideae (<em>Melocactus bahiensis</em>, <em>Melocactus curvispinus</em>, <em>Echinopsis eyriesii</em>, <em>E. mirablis</em>, <em>E. peruviana</em>, <em>Oreocereus celsianus</em>, <em>Rebutia flavistyla</em>, <em>Rebutia minuscula</em>, <em>Astrophytum myriostigma</em>, <em>Mamillaria columbiana</em>, and <em>M. prolifera</em>) have been studied. These plants exhibit a uniseriate epidermis, covered by a thin cuticle. Except for <em>E. peruviana</em> and <em>A. myriostigma</em>, no hypodermis could be detected. The shoots of all studied specimens consist mainly of cortex parenchyma with large thin-walled cells. The pith parenchyma is composed of much smaller cells. Due to the fact that the cortex parenchyma comprises the largest portion of the cross-sectional area, it can be concluded that it is the main water-storing tissue. The extent of vascular tissue development varies. Collateral vascular bundles are present in the stele. The studied seedlings contain various ergastic substances, in particular inclusions of calcium oxalate (all studied species), starch (<em>Mammillaria prolifera</em>, <em>E. mirabilis</em>, and the genus <em>Melocactus</em>), inulin-like inclusions, and occasionally lipid drops (some <em>Echinopsis</em> species).</p><p>Thus, it was found that all studied plants have a highly specialized anatomical and morphological structure. At the same time, the epidermis and hypodermis are poorly developed. Accordingly, the adaptation to arid conditions of the examined seedlings involves an increased growth of the water-storing tissue and the production of ergastic substances.</p>

Raman Spectroscopy Study of Calcium Oxalate Extracted from Cacti Stems

To find markers that distinguish the different Cactaceae species, by using near infrared Raman spectroscopy and scanning electron microscopy, we studied the occurrence, in the stem, of solid deposits in five Cactaceae species (Coryphantha clavata, Ferocactus latispinus, Opuntia ficus-indica, O. robusta, and O. strepthacantha) collected from their natural habitats from a region of México. The deposits in the tissues usually occurred as spheroidal aggregates, druses, or prismatic crystals. From the Raman spectra, the crystals were identified either as calcium oxalate monohydrate (CaC2O4·H2O) or calcium oxalate dihydrate (CaC2O4·2H2O). Opuntia species (subfamily Opuntioideae) showed the presence of CaC2O4·H2O, and the deposition of CaC2O4·2H2O was present in C. clavata and F. latispinus (subfamily Cactoideae, Cacteae tribe). As a punctual technique, Raman spectroscopy seems to be a useful tool to identify crystal composition. In addition to allowing the analysis of crystal morphology, this spectroscopic technique can be used to identify Cactaceae species and their chemotaxonomy.

Functional morphology and biomechanics of branch–stem junctions in columnar cacti

Branching in columnar cacti features morphological and anatomical characteristics specific to the subfamily Cactoideae. The most conspicuous features are the pronounced constrictions at the branch-stem junctions, which are also present in the lignified vascular structures within the succulent cortex. Based on finite-element analyses of ramification models, we demonstrate that these indentations in the region of high flexural and torsional stresses are not regions of structural weakness (e.g. allowing vegetative propagation). On the contrary, they can be regarded as anatomical adaptations to increase the stability by fine-tuning the stress state and stress directions in the junction along prevalent fibre directions. Biomimetic adaptations improving the functionality of ramifications in technical components, inspired, in particular, by the fine-tuned geometrical shape and arrangement of lignified strengthening tissues of biological role models, might contribute to the development of alternative concepts for branched fibre-reinforced composite structures within a limited design space.

The systematic significance of floral morphology, nectaries, and nectar concentration in epiphytic cacti of tribes Hylocereeae and Rhipsalideae (Cactaceae)

A long-standing interest in cactus taxonomy has existed since the Linnaean generation, but an appreciation of the reproductive biology of cacti started early in the 1900s. Numerous studies indicate that plant reproductive traits provide valuable systematic information. Despite the extensive reproductive versatility and specializations in breeding systems coupled with the striking floral shapes, the reproductive biology of the Cactaceae has been investigated in approximately 10% of its species. Hence, the systematic value of architectural design and organization of internal floral parts has remained virtually unexplored in the family. This study represents the most extensive survey of flower and nectary morphology in the Cactaceae focusing on tribes Hylocereeae and Rhipsalideae (subfamily Cactoideae). Our objectives were (1) to conduct comparative morphological analyses of flowers and floral nectaries and (2) to compare nectar solute concentration in these two tribes consisting of holo- and semi-epiphytic species. Flower morphology, nectary types, and sugar concentration of nectar have strong taxonomic implications at the tribal, generic and specific levels. Foremost, three types of nectaries were found, namely chamber nectary (with the open and diffuse subtypes), furrow nectary (including the holder nectary subtype), and annular nectary. All Hylocereeae species possess chamber nectaries, in which the nectarial tissue has both trichomes and stomata. The Rhipsalideae are distinguished by two kinds of floral nectaries: furrow and annular, both nectary types with stomata only. The annular nectary type characterizes the genus Rhipsalis. Nectar concentration is another significant taxonomic indicator separating the Hylocereeae and Rhipsalideae and establishing trends linked to nectar sugar concentration and amount of nectar production in relation to flower size. There is an inverse relationship between flower size and amount of nectar production in the smaller Rhipsalideae flowers, in which nectar concentration is more than two-fold higher despite the smaller volume of nectar produced when compared to the large Hylocereeae flowers. Variability of nectary morphology and nectar concentration was also evaluated as potential synapomorphic characters in recent phylogenies of these tribes. In conclusion, our data provide strong evidence of the systematic value of floral nectaries and nectar sugar concentration in the Cactaceae, particularly at different taxonomic levels in the Hylocereeae and Rhipsalideae.

DNA barcodes for Mexican Cactaceae, plants under pressure from wild collecting

DNA barcodes could be a useful tool for plant conservation. Of particular importance is the ability to identify unknown plant material, such as from customs seizures of illegally collected specimens. Mexican cacti are an example of a threatened group, under pressure because of wild collection for the xeriscaping trade and private collectors. Mexican cacti also provide a taxonomically and geographically coherent group with which to test DNA barcodes. Here, we sample the matK barcode for 528 species of Cactaceae including approximately 75% of Mexican species and test the utility of the matK region for species-level identification. We find that the matK DNA barcode can be used to identify uniquely 77% of species sampled, and 79-87% of species of particular conservation importance. However, this is far below the desired rate of 95% and there are significant issues for PCR amplification because of the variability of primer sites. Additionally, we test the nuclear ITS regions for the cactus subfamily Opuntioideae and for the genus Ariocarpus (subfamily Cactoideae). We observed higher rates of variation for ITS (86% unique for Opuntioideae sampled) but a much lower PCR success, encountering significant intra-individual polymorphism in Ariocarpus precluding the use of this marker in this taxon. We conclude that the matK region should provide useful information as a DNA barcode for Cactaceae if the problems with primers can be addressed, but matK alone is not sufficiently variable to achieve species-level identification. Additional complementary regions should be investigated as ITS is shown to be unsuitable.

Molecular systematics of the Cactaceae.

Bayesian, maximum-likelihood, and maximum-parsimony phylogenies, constructed using nucleotide sequences from the plastid gene region trnK-matK, are employed to investigate relationships within the Cactaceae. These phylogenies sample 666 plants representing 532 of the 1438 species recognized in the family. All four subfamilies, all nine tribes, and 69% of currently recognized genera of Cactaceae are sampled. We found strong support for three of the four currently recognized subfamilies, although relationships between subfamilies were not well defined. Major clades recovered within the largest subfamilies, Opuntioideae and Cactoideae, are reviewed; only three of the nine currently accepted tribes delimited within these subfamilies, the Cacteae, Rhipsalideae, and Opuntieae, are monophyletic, although the Opuntieae were recovered in only the Bayesian and maximum-likelihood analyses, not in the maximum-parsimony analysis, and more data are needed to reveal the status of the Cylindropuntieae, which may yet be monophyletic. Of the 42 genera with more than one exemplar in our study, only 17 were monophyletic; 14 of these genera were from subfamily Cactoideae and three from subfamily Opuntioideae. We present a synopsis of the status of the currently recognized genera. © The Willi Hennig Society 2011.

What is the role of hybridization in the evolution of the Cactaceae?

Summary: Natural hybridization has been frequently reported in Cactaceae, but there are few studies on the impact of hybridization in the evolution and diversification of this family. The majority of the studies that have addressed this subject have been restricted to the subfamily Opuntioideae. Little is known about the role of hybridization on the more diverse subfamily Cactoideae. This paper discusses putative examples of hybrid lineages in subfamily Cactoideae, focussing on examples of lineages for which hybrid or introgressive origin have been confirmed or deduced from morphological and molecular studies. These examples suggest that natural hybridization may have played an important role in the evolution and diversification of taxa in Cactaceae, and further studies of hybrid lineages may provide us with important insights on the evolution of this family.

Anatomy of Brazilian Cereeae (subfamily Cactoideae, Cactaceae): Arrojadoa Britton & Rose, Stephanocereus A. Berger and Brasilicereus Backeberg

(Anatomy of Brazilian Cereeae (subfamily Cactoideae, Cactaceae): Arrojadoa Britton & Rose, Stephanocereus A. Berger wâBrasilicereus Backeberg). Arrojadoa, Stephanocereus and Brasilicereus are endemic Brazilian Cereeae, occurring along the Espinhaço Range, in the campos rupestres, cerrados and caatingas, from northern Minas Gerais to southern Bahia. The genera are columnar, erect to semi-erect cacti, except for one species, A bahiensis, which is globose. This study describes the anatomy of dermal, fundamental and vascular systems, aiming to find diagnostic characters for the genera and species. Basal portions of stems were sectioned transversely and longitudinally, and stained with Astrablue and Safranin. The species share a uniseriate epidermis, with thick cuticle; well developed collenchymatic hypodermis, containing prismatic crystals; cortex with numerous mucilage cells, druses and vascular bundles; outside cortex as a palisade parenchyma; periderm composed of lignified cork cells alternating with suberized cells; pheloderm consisting of a few layers of thin-walled cells; phloem composed of solitary or multiple of two to three sieve tube elements, companion cells, axial and radial parenchyma; secondary xylem with solitary to multiple vessels, with simple perforation plates and alternate bordered to semi-bordered pits; axial parenchyma scanty vasicentric to incomplete; libriform septate fibres; large rays. Unlignified parenchyma is seen in the secondary xylem, varying from a few cells to bands among axial and radial elements. The following are considered diagnostic characters: the shape of lignified phellem cells, cubic to radially elongate, which individualizes S. leucostele; an underdeveloped hypodermis and the occurrence of sclereids in the cortex are exclusive to Brasilicereus markgrqfii.

Vivipary in coastal cacti: a potential reproductive strategy in halophytic environments

Vivipary, the germination of seeds within the fruit prior to abscission from the maternal plant, is an important event in plants. Two main types of vivipary are known in vascular plants: true vivipary and pseudovivipary. In crop grasses, pseudovivipary is an undesirable character as it results in lower yields. To date, vivipary in the Cactaceae has been reported for less than 20 species, most of which are cultivated. Here, we report viviparous (cryptoviviparous-a subcategory of true vivipary) cacti in nature in members of the tribes Cacteae and Pachycereeae (subfamily Cactoideae). We present four species inhabiting coastal plains in areas subject to periodic flooding, namely, Ferocactus herrerae, Stenocereus alamosensis, S. thurberi, and Pachycereus schottii. These species from localities in northwestern Mexico had viviparous fruits and offspring in different stages of development. A potential trend in the data indicates that the overall proportion of viviparous plants is higher in coastal flooding areas relative to halophytic, nonflooding areas. In our view, vivipary is a reproductive strategy that has evolved to provide a more efficient mechanism favoring germination and new avenues for survival by contributing to population maintenance and short-distance dispersal on halophytic substrates.

Tiny but Complex Foliage Leaves Occur in Many “Leafless” Cacti (Cactaceae)

Most cacti in subfamily Cactoideae have tiny foliage leaves (most less than 1.5 mm long) hidden by enlarged axillary buds (the spine clusters). Leaf development similar to that of Arabidopsis and other model plants occurs in six species that have a rudimentary lamina, mesophyll, vascular tissue, stomata, and dorsiventral asymmetry. In the other 141 species, mature foliage leaves are progressively simpler, as if development stops at different points during otherwise ordinary morphogenesis. In 21 species, development stops at the leaf primordium stage, and in 52 species, mature leaves are up to 500 μm tall (distinctly larger than primordia) but consist of just ground tissue and ordinary epidermis cells. Mature leaves in 71 species are elongate (500–2500 μm) cones of epidermis and ground tissue, with xylem near the adaxial side (phloem was detected in only four species); most conical leaves have abaxial stomata. Chlorenchyma is universally present in mesophyll; mucilage and druses occur in some species. Leaf reduction may have reduced auxin production: long, complex leaves occur on columnar plants; short, simple leaves are on globose plants. Expression of genes such as KNOX, PHANTASTICA, and YODA were probably modified during leaf evolution in cacti.