Developmental Reaction Norms for Water Stressed Seedlings of Succulent Cacti

Succulent cacti are remarkable plants with capabilities to withstand long periods of drought. However, their adult success is contingent on the early seedling stages, when plants are highly susceptible to the environment. To better understand their early coping strategies in a challenging environment, two developmental aspects (anatomy and morphology) in Polaskia chichipe and Echinocactus platyacanthus were studied in the context of developmental reaction norms under drought conditions. The morphology was evaluated using landmark based morphometrics and Principal Component Analysis, which gave three main trends of the variation in each species. The anatomy was quantified as number and area of xylem vessels. The quantitative relationship between morphology and anatomy in early stages of development, as a response to drought was revealed in these two species. Qualitatively, collapsible cells and collapsible parenchyma tissue were observed in seedlings of both species, more often in those subjected to water stress. These tissues were located inside the epidermis, resembling a web of collapsible-cell groups surrounding turgid cells, vascular bundles, and spanned across the pith. Occasionally the groups formed a continuum stretching from the epidermis towards the vasculature. Integrating the morphology and the anatomy in a developmental context as a response to environmental conditions provides a better understanding of the organism's dynamics, adaptation, and plasticity

A taxonomic backbone for the global synthesis of species diversity in the angiosperm order Caryophyllales

The Caryophyllales constitute a major lineage of flowering plants with approximately 12500 species in 39 families. A taxonomic backbone at the genus level is provided that reflects the current state of knowledge and accepts 749 genera for the order. A detailed review of the literature of the past two decades shows that enormous progress has been made in understanding overall phylogenetic relationships in Caryophyllales. The process of re-circumscribing families in order to be monophyletic appears to be largely complete and has led to the recognition of eight new families (Anacampserotaceae, Kewaceae, Limeaceae, Lophiocarpaceae, Macarthuriaceae, Microteaceae, Montiaceae and Talinaceae), while the phylogenetic evaluation of generic concepts is still well underway. As a result of this, the number of genera has increased by more than ten percent in comparison to the last complete treatments in the Families and genera of vascular plants” series. A checklist with all currently accepted genus names in Caryophyllales, as well as nomenclatural references, type names and synonymy is presented. Notes indicate how extensively the respective genera have been studied in a phylogenetic context. The most diverse families at the generic level are Cactaceae and Aizoaceae, but 28 families comprise only one to six genera. This synopsis represents a first step towards the aim of creating a global synthesis of the species diversity in the angiosperm order Caryophyllales integrating the work of numerous specialists around the world

Coexistence and the niche in a nurse-cactus interaction: is cyclic dynamics justified?

1. The interaction between the nurse plant Larrea tridentata and the cacti Cylindropuntia leptocaulis is thought to follow cyclical-replacement dynamics. However, the required changing nature of their interaction, from facilitation to competition, has not been investigated through their full life cycle. 2. In order to test the hypothesised cyclical dynamics, we compared the demography of four sub-populations (LA = Larrea associated to Cylindropuntia; CA = Cylindropuntia associated to Larrea, LS = solitary Larrea; CS = solitary Cylindropuntia) in the Mapimí Biosphere Reserve, Mexico, over the period 2008-2015. This allowed us to compare their demography at varying levels of the generally low and unpredictable limiting resource, water. Given the protection afforded to C. leptocaulis seedlings by L. tridentata and their presumed increasingly competitive effect on L. tridentata, which would justify the expectation of cyclic replacement dynamics, we expected to find a zero or positive per capita rate of population growth (r≥0) in CA and LS, and a negative one in CS and LA. 3. The overall r over the study period was close to equilibrium (r=0) for both LA and LS, with no significant difference between them. In contrast, and as expected, r of CA was consistently and significantly larger than that for CS. In both species, λ (=er) was positively correlated with annual rainfall with no significant difference between LA and LS and a significant difference between CA and CS in this relationship. L. tridentata can exist alone and coexist with C. leptocaulis across the levels of precipitation experienced at the study site, while C. leptocaulis cannot persist in the absence of L. tridentata. The cyclical dynamics of replacement does not occur in this system and, given the static nature of the evidence on which the original conclusion was based, it is unlikely to exist as a general rule across the species’ geographic range. 4. Synthesis: Our findings stress the importance of elucidating the demographic mechanisms that allow species competing for a common limiting resource to coexist when the resource varies temporally, and expose the difficulty of identifying a species’ ecological niche in the absence of detailed, long-term demographic information