Stigma morphology in Aylostera subg. Mediolobivia (Cactaceae) and its importance for systematic investigation

The stigma of 31 taxa of Aylostera (Cactaceae) was studied using environmental scanning electron microscopy. Seven stigma types could be defined, based on the degree of fusion of the stigmatic lobes and, when these are completely separated (types I and II), their orientation. Four types (types IV, V, VI and VII) are present only in Aylostera subg. Mediolobivia, two of which (types IV and VII) are species-specific. Stigma morphology was found to be a good diagnostic character in Aylostera subg. Mediolobivia, allowing in some cases to distinguish species that had been confused previously. The stigmatic types here defined seem apt to characterize natural groups within the subgenus and are useful as an aid for species identification and the characterization of new taxa.     

Effect of brousse tigrée on the dynamics of nurse–protégé interactions of a cactus in the Chihuahuan Desert

A nurse–protégé relationship is a frequent facilitation interaction in deserts that allows the recruitment of new individuals of many species. Our aim was to evaluate the relationship of Echinocereus enneacanthus during its life cycle and its nurse plants in the brousse tigrée (tiger bush) vegetation of the Chihuahuan Desert. The population structure of the cactus is skewed toward adult stages, which are commonly found in the bare areas of the brousse tigrée, whereas juveniles are located in the vegetated bands. The vegetation structure and the nurse–protégé relationship were determined using censuses of 19 permanent plots monitored between 2008 and 2019. The differential association of E. enneacanthus with potential nurse plants was evaluated using an interaction network, under the hypothesis of strict association of the seedlings and juveniles with nurse species. In addition, χ² tests and standardized residuals were fitted among likely nurse species, weighted by the cover of the nurse and of the areas without vegetation. The study species, as well as the nurse plants, had an aggregated distribution pattern. The interaction network showed that the frequency of the association with nurse plants decreased as the size of the protégé individuals increased. At the same time, there were differences in the establishment of E. enneacanthus under particular nurse plants; Prosopis glandulosa and Hilaria mutica were the most important. The nurse–protégé relationship for seeds and seedlings is integral to the vegetation bands of the brousse tigrée.     

Regeneration of roots from callus reveals stability of the developmental program for determinate root growth in Sonoran Desert Cactaceae

In some Sonoran Desert Cactaceae the primary root has a determinate root growth: the cells of the root apical meristem undergo only a few cell division cycles and then differentiate. The determinate growth of primary roots in Cactaceae was found in plants cultivated under various growth conditions, and could not be reverted by any treatment tested. The mechanisms involved in root meristem maintenance and determinate root growth in plants remain poorly understood. In this study, we have shown that roots regenerated from the callus of two Cactaceae species, Stenocereus gummosus and Ferocactus peninsulae, have a determinate growth pattern, similar to that of the primary root. To demonstrate this, a protocol for root regeneration from callus was established. The determinate growth pattern of roots regenerated from callus suggests that the program of root development is very stable in these species. These findings will permit future analysis of the role of certain Cactaceae genes in the determinate pattern of root growth via the regeneration of transgenic roots from transformed calli.     

The closest relatives of cacti: insights from phylogenetic analyses of chloroplast and mitochondrial sequences with special emphasis on relationships in the tribe Anacampseroteae

Recent molecular and morphological systematic investigations revealed that the cacti are most closely related to Anacampseroteae, Portulaca and Talinum of the family Portulacaceae (ACPT clade of suborder Portulacineae). A combined analysis of ndhF, matK, and nad1 sequence data from the chloroplast and the mitochondrial genomes indicates that the tribe Anacampseroteae is the sister group of the family Cactaceae. This clade, together with Portulaca, is well characterized by the presence of axillary hairs or scales. Relationships within Anacampseroteae are characterized by a grade of five species of Grahamia s.l. from North and South America, and Grahamia australiana is found to be sister to the genera Anacampseros and Avonia. A comparison of vegetative characteristics indicates an evolutionary transition from woody subshrubs to dwarf perennial and highly succulent herbs during the diversification of Anacampseroteae. Available evidence from the present investigation as well as from previously published studies suggests that a revised classification of Portulacineae on the basis of inferred phylogenetic relationships might consist of a superfamily that includes Cactaceae and the three genera Anacampseros s.l. (including Avonia and Grahamia s.l.), Portulaca, and Talinum (including Talinella), either referred to three monogeneric families or to a paraphyletic family Portulacaceae*.     

Dactylopius opuntiae,a new prickly pear cactus pest in the Mediterranean: an overview

The Opuntia cochineal scale or false carmine cochineal scale, Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae), is spreading rapidly in many countries, especially in the Mediterranean basin, where it has become a serious pest of prickly pear crops, Opuntia ficus‐indica (L.) Miller (Cactaceae). This crop is an important food resource both for humans and livestock. The cochineal was originally used as a biological agent to control cactaceous weeds in many countries where Opuntiaceae had been introduced. Currently, in some countries where the prickly pear is no longer considered a weed but a productive crop, as in the Mediterranean area, D. opuntiae has changed its role from a highly prized biological control agent to the status of serious pest. This paper provides an overview of the current knowledge on D. opuntiae for farmers and stakeholders in order to indicate the most appropriate way to limit or counteract the spread of this pest especially in new cultivated areas.     

Secondary metabolites from Opuntia ficus-indica var. saboten

A butanol fraction, from the methanolic extract of Opuntia ficus-indica var. saboten, on purification either by preparative TLC or reversed phase HPLC, yielded three chemical components: isorhamnetin 3-O-(6'-O-E-feruloyl)neohesperidoside (1), (6R)-9,10-dihydroxy-4,7-megastigmadien-3-one-9-O-beta-D-glucopyranoside (2) and (6S)-9,10-dihydroxy-4,7-megastigmadien-3-one-9-O-beta-D-glucopyranoside (3) along with 15 known compounds. Structures of compounds (1-3) were elucidated by aid of spectroscopic analyses. The absolute stereochemistry in compounds 2 and 3 was established with the help of CD data analysis and comparison with the literature data. In a DPPH radical scavenging assay, compound 1 showed moderate inhibitory activity (IC50 = 45.58 microg/ml).     

Vivipary in the Cactaceae: Its taxonomic occurrence and biological significance

Vivipary, a rare reproductive strategy in flowering plants, has been previously reported in only four species of the Cactaceae. In this paper, eight additional examples (Cleistocactus smaragdiflorus, Disocactus martianus, the hybrid Epiphyllum X Fern la Borde, Harrisia martinii, Lepismium ianthothele, L. monacanthum, Rhipsalis micrantha forma micrantha, and R. baccifera subsp. horrida) of vivipary in cultivated cacti from tribes Hylocereeae, Rhipsalideae, and Trichocereeae are documented. The plants had fully-developed and mature fruits containing seeds at different stages of germination, including tiny embryos emerging from the seed coat to young, healthy seedlings with well-developed organs, such as cotyledons and radicles. Several features, though not unique, distinguish cactus fruits with viviparous seedlings. Foremost, the fruits are fleshy with abundant mucilage and a relatively thick, often transparent pericarp. The seeds are generally numerous and embedded in a transparent, white or red pulp. The occurrence of vivipary in taxa from four phylogenetically distinct tribes of the subfamily Cactoideae suggests an independent origin and indicates that this reproductive strategy may be more widespread in the family than originally thought. Vivipary in the Cactaceae is regarded as a form of cryptovivipary, a condition in which the zygote develops inside the fruit without penetrating the ovary wall for dispersal purposes, which in turn is considered a subcategory of true vivipary. Further, vivipary is interpreted as an adaptive reproductive strategy that enables seedlings to establish more rapidly.     

Variation in age and height of onset of reproduction in the saguaro cactus (<Emphasis Type="Italic">Carnegiea gigantea</Emphasis>) in the Sonoran Desert

The objective of this study is to determine the height and age at which reproduction begins (i.e., production of flowers and fruits; the transition to adulthood) in the giant saguaro cactus (Carnegiea gigantea) in four geographically and environmentally distinct populations, and to relate observed variability to environmental differences. The onset of reproduction has been estimated at a height of 2.2 m in near optimal conditions. This value has been widely accepted and applied to populations in less optimal conditions, although variations under less ideal conditions have not been investigated. In addition, previous research has demonstrated that Carnegiea growth rates are highly variable over their range. Thus, even if 2.2 m is a consistent transition height to adulthood over their range, the age of individuals in different populations would be different. I investigate the age and height at which this transition occurs. The author sampled the heights of the shortest reproductive individuals and the tallest non-reproductive individuals to estimate the mean height of the onset of flowering in each of four locales in the northern Sonoran Desert. Using a previously published age-height-growth model, the mean age of the start of reproduction was also computed for the four sites. ANOVA and t-tests were used to compare the average transition to adulthood across sites by both age and height. Statistical results are robust and significant variations in the onset of reproduction are observed by both age and height across the four sites. Saguaro National Park and Organ Pipe Cactus National Monument individuals are transitioning to adulthood, on average, at younger ages and shorter heights than the other two locales. At the arid and marginal Kofa site, individuals that established during the regeneration peak of the late 1800s-early 1900s are only now becoming reproductive (individuals that established around 1899), while at Saguaro National Park, on average, individuals that established in the 1950s are already transitioning to adulthood. These results have implications for regeneration, particularly in marginal locales where regeneration is already limited.     

Thermal buffering capacity of the germination phenotype across the environmental envelope of the Cactaceae

Recruitment from seeds is among the most vulnerable stage for plants as global temperatures change. While germination is the means by which the vast majority of the world's flora regenerate naturally, a framework for accurately predicting which species are at greatest risk of germination failure during environmental perturbation is lacking. Taking a physiological approach, we assess how one family, the Cactaceae, may respond to global temperature change based on the thermal buffering capacity of the germination phenotype. We selected 55 cactus species from the Americas, all geo‐referenced seed collections, reflecting the broad environmental envelope of the family across 70° of latitude and 3700 m of altitude. We then generated empirical data of the thermal germination response from which we estimated the minimum (T_b), optimum (T_o) and ceiling (T_c) temperature for germination and the thermal time (θ₅₀) for each species based on the linearity of germination rate with temperature. Species with the highest T_b and lowest T_c germinated fastest, and the interspecific sensitivity of the germination rate to temperature, as assessed through θ₅₀, varied tenfold. A left‐skewed asymmetry in the germination rate with temperature was relatively common but the unimodal pattern typical of crop species failed for nearly half of the species due to insensitivity to temperature change at T_o. For 32 fully characterized species, seed thermal parameters correlated strongly with the mean temperature of the wettest quarter of the seed collection sites. By projecting the mean temperature of the wettest quarter under two climate change scenarios, we predict under the least conservative scenario (+3.7°C) that 25% of cactus species will have reduced germination performance, whilst the remainder will have an efficiency gain, by the end of the 21st century.