Pereskia and the Origin of the Cactus Life-Form

Abstract

The cactus life-form is cited as an example of a tight relationship between organism form and function: a succulent, long-lived, photosynthetic stem allows cacti to survive long periods of drought while maintaining a positive tissue water status. Pereskia (Cactaceae) comprises 17 species of leafy shrubs and trees that are thought to represent the original cactus condition. Recent phylogenetic work has shown that there are two separate clades of Pereskia species, which are basal and paraphyletic with respect to the rest of the cacti. We selected seven Pereskia species, representing both clades, and characterized their water relations by measuring a suite of physiological traits in wild populations. Additionally, we estimated basic climate parameters from collection localities for all 17 Pereskia species. Extant Pereskia species exhibit ecological water use patterns that are very similar to those of the leafless, stem-succulent cacti. Ancestral trait reconstruction for the physiological and environmental data provides a preliminary assessment of the ecology and water relations of the earliest cacti and suggests that several key elements of the cactus ecological niche were established before the evolution of the cactus life-form. We interpret these ecological traits as potentially important drivers of evolutionary innovation in the cacti.

Anatomical variation in Cactaceae and relatives: Trait lability and evolutionary innovation

“…The ability to sequester calcium ions in this manner may be relevant for the correct functioning of stem stomata. It is interesting to consider the strong support for the correlated evolution of hypodermal druses and stem stomata in our data set (Table 4); currently, however, there is not much evidence that these traits are functionally linked, because stem stomata in the Andean/SSA Pereskia lineage do not appear to be heavily involved in gas exchange (Martin and Wallace, 2000; Edwards and Donoghue, 2006). An alternative explanation for a functional role of hypodermal druses may be as a deterrent to herbivory, which would be important in plants that are lacking the protective functions of an early periderm.…”

“…Although no character perfectly distinguishes the two Pereskia clades, all northern clade species have precocious stem periderm onset and lack stem stomata, while most Andean/SSA clade species have delayed stem periderm (except P. aculeata ) and possess stem stomata (except P. nemorosa ). No Pereskia species have been reported to engage in significant photosynthetic carbon uptake through the stem (Nobel and Hartsock, 1986; Martin and Wallace, 2000; Edwards and Donoghue, 2006), but the presence of stem stomata and delayed periderm unites the Andean/SSA species with the most speciose cactus lineages, Opuntioideae and Cactoideae (“core cacti” of Edwards et al, 2005). The changes in these characters subsequent to the divergence of the northern Pereskia lineage from other cacti may have therefore been important preconditions for the evolution of the functionally leafless, stem‐photosynthetic life form of the core cacti.…”

Timing of morphological and ecological innovations in the cyanobacteria – a key to understanding the rise in atmospheric oxygen

“…Although used in evolutionary studies of macroscopic eukaryotes (e.g. Edwards & Donoghue, 2006;Endress & Doyle, 2009;Price et al, 2009), ASR is just beginning to be applied toward prokaryotic taxa (Blank, 2004(Blank, , 2009aSánchez-Baracaldo et al, 2005). We addressed the need for dense taxonomic sampling by using several molecular data sets (SSU-LSU, SSU-RpoC, 139 genes) that had overlapping sets of taxa.…”

3D‐Printed Cactus‐Inspired Spine Structures for Highly Efficient Water Collection

“…For example, Namibia Desert beetles and spider silks can efficiently collect water from the fog . Many members of the Cactaceae family can survive in highly arid deserts by using spines that collect fog from multiple directions . The gradient of surface‐free energy and gradient of Laplace pressure are the primary driving forces behind these phenomena .…”