Urs Eggli

Contemporaneous and recent radiations of the world's major succulent plant lineages.

The cacti are one of the most celebrated radiations of succulent plants. There has been much speculation about their age, but progress in dating cactus origins has been hindered by the lack of fossil data for cacti or their close relatives. Using a hybrid phylogenomic approach, we estimated that the cactus lineage diverged from its closest relatives ≈35 million years ago (Ma). However, major diversification events in cacti were more recent, with most species-rich clades originating in the late Miocene, ≈10–5 Ma. Diversification rates of several cactus lineages rival other estimates of extremely rapid speciation in plants. Major cactus radiations were contemporaneous with those of South African ice plants and North American agaves, revealing a simultaneous diversification of several of the worlds major succulent plant lineages across multiple continents. This short geological time period also harbored the majority of origins of C4 photosynthesis and the global rise of C4 grasslands. A global expansion of arid environments during this time could have provided new ecological opportunity for both succulent and C4 plant syndromes. Alternatively, recent work has identified a substantial decline in atmospheric CO2 ≈15–8 Ma, which would have strongly favored C4 evolution and expansion of C4-dominated grasslands. Lowered atmospheric CO2 would also substantially exacerbate plant water stress in marginally arid environments, providing preadapted succulent plants with a sharp advantage in a broader set of ecological conditions and promoting their rapid diversification across the landscape.

Living under temporarily arid conditions - succulence as an adaptive strategy

Summary: Succulence is an adaptive strategy that allows plants to remain active during seasonal water shortage. The term was first used formally by Johann (Jean) Bauhin in 1619 to refer to plants with thick, juicy leaves. Its subsequent use and selected definitions are critically discussed, including concepts such as utilizable water, caudiciforms and pachycauls, and root succulence. A unified definition of succulence considers aspects of morphology and anatomy, ecology, and physiology. Stem succulence and the “cactus life form” are used to illustrate the parallel evolution of functional adaptations in morphology, and to contrast the obvious external similarities with the widely variable internal architecture, including the participation of different stem tissues in water storage.

Variations On A Theme: Repeated Evolution Of Succulent Life Forms In the Portulacineae (Caryophyllales)

Abstract The succulent life form is a tried and true strategy for plants living in arid environments. It has evolved in many distantly related lineages comprising 12,500 species from 70 flowering plant families and has spawned remarkable radiations. Three major groups are generally recognized: (1) stem succulents (that is, leafless cactus-like growth forms), (2) leaf succulents, and (3) caudiciform and pachycaul succulents. All three lifeform groups are represented in the relatively small suborder Portulacineae. Here we suggest that this diversity provides a unique opportunity to evaluate early cactus evolution within a richer contextual framework. We briefly review what we know about the phylogenetic relationships within the suborder Portulacineae (that is, Basellaceae, Cactaceae, Didiereaceae, and Portulacaceae) and the morphology and ecology of all major Portulacineae lineages. We then outline what we believe to be key areas for future research on these understudied plants and discuss several hypothetical “pre-adaptations” and conditions in ancestral Portulacineae that may have promoted the repeated evolution of unusual succulent life forms.

NOTEWORTHY IDIOBLASTIC SCLEREIDS IN THE STEMS OF EULYCHNIA (CACTACEAE)

Stems of Eulychnia (a genus of six to nine species of candelabriform or arborescent cacti) have a parenchymatic cortex with two distinct regions. The outer chlorenchymatic layer is characterized by a conspicuous parallel striping, whereas the inner cortex region devoid of chlorophyll has a coarsely granular aspect. Stem samples from nine accessions, collected in the field or taken from cultivation, were studied from resin-embedded microtome sections and maceration. Two different forms of lignified sclereids were found dispersed in the cortex and the pith. The sclereids of the outer palisade-like cortex layer are distinctly elongated and strictly oriented at right angle to the stem surface, whereas those of the inner cortex and pith are globular or subglobular and conspicuously enlarged compared with the surrounding parenchyma cells. The ontogeny of the sclereids was studied from stem samples of different ages. Formation of the secondary cell walls starts only after cell growth is completed. A screening of numerous South American cacti for the presence of idioblastic sclereids showed that these structures are unique for the genus Eulychnia. Finally, functional aspects of the sclereids are shortly discussed. It is assumed that the sclereids contribute to the mechanical support and reinforcement of the plants.

An up-to-date familial and suprafamilial classification of succulent plants

Summary: We provide a short discussion of how the use of molecular data and sophisticated analytical methods has expanded our knowledge about the phylogenetic relationships among flowering plants and how this affects the familial and suprafamilial classification of succulents. A tree diagram illustrates the current hypothesis on their interrelationships and a table lists all 83 families that include succulent representatives (c.12,500 species from c.690 genera), together with information on taxonomic diversity (i.e. number of estimated species and genera) and architectural types of succulence. Furthermore, we briefly discuss some important recent modifications to the family classification of flowering plants and provide arguments for the proposed changes as far as succulents are concerned. In particular, we focus on the controversially discussed family classification of the monocotyle-donous order Asparagales and provide arguments for a revised classification that considers the distinct variation patterns in this clade.

A Bibliography of Succulent Plant Periodicals

Summary. A classified list of periodicals devoted entirely or in part to succulent plants is given. Relevant bibliographical information is provided for each title, as well as a consistent set of abbreviations. Important sub-titles, alternative titles, etc., are always cross-referenced to the main entry. Two appendices list the periodicals according to publishing country and subjects, respectively.

Type specimens of Cactaceae names in the Berlin Herbarium (B)

Abstract Eggli, U. & Leuenberger, B. E.: Type specimens of Cactaceae names in the Berlin Herbarium (B) [De herbario berolinensi notulae 48]. — Willdenowia 38: 213–280. — ISSN 0511-9618;

The Cárdenas type specimens of Cactaceae names in the herbarium of the Instituto Miguel Lillo, Tucumán, Argentina (LIL)

Abstract Eggli, U. & Leuenberger, B. E.: The Cárdenas type specimens of Cactaceae names in the herbarium of the Instituto Miguel Lillo, Tucumán, Argentina (LIL). — Willdenowia 35: 179–192.-ISSN 0511-9618;

On colour forms of Opuntia weberi (Cactaceae) with notes on the typification of the name

Abstract Eggli, U. & Leuenberger, B. E.: On colour forms of Opuntia weberi (Cactaceae) with notes on the typification of the name. — Willdenowia 28: 175–180. 1998. — ISSN 0511-9618. A pink-flowered population of Opuntia weberi is reported from San Juan Province, Argentina. The variation and geographical distribution of the species are discussed. Investigation of the extant original material confirms the choice of a type specimen by Kiesling in 1984 to be appropriate.

From cacti to carnivores: Improved phylotranscriptomic sampling and hierarchical homology inference provide further insight into the evolution of Caryophyllales

PREMISE OF THE STUDY The Caryophyllales contain ~12,500 species and are known for their cosmopolitan distribution, convergence of trait evolution, and extreme adaptations. Some relationships within the Caryophyllales, like those of many large plant clades, remain unclear, and phylogenetic studies often recover alternative hypotheses. We explore the utility of broad and dense transcriptome sampling across the order for resolving evolutionary relationships in Caryophyllales. METHODS We generated 84 transcriptomes and combined these with 224 publicly available transcriptomes to perform a phylogenomic analysis of Caryophyllales. To overcome the computational challenge of ortholog detection in such a large data set, we developed an approach for clustering gene families that allowed us to analyze >300 transcriptomes and genomes. We then inferred the species relationships using multiple methods and performed gene-tree conflict analyses. KEY RESULTS Our phylogenetic analyses resolved many clades with strong support, but also showed significant gene-tree discordance. This discordance is not only a common feature of phylogenomic studies, but also represents an opportunity to understand processes that have structured phylogenies. We also found taxon sampling influences species-tree inference, highlighting the importance of more focused studies with additional taxon sampling. CONCLUSIONS Transcriptomes are useful both for species-tree inference and for uncovering evolutionary complexity within lineages. Through analyses of gene-tree conflict and multiple methods of species-tree inference, we demonstrate that phylogenomic data can provide unparalleled insight into the evolutionary history of Caryophyllales. We also discuss a method for overcoming computational challenges associated with homolog clustering in large data sets.