On the evolutionary origins of the cacti

Abstract

On the evolutionary origins of the cacti. -Taxon 46: 217-232. 1997. -ISSN 0040-0262.Understanding evolutionary responses of plants to desert environments depends upon phylogenetic knowledge of desert plants. The diverse American desert family Cactaceae has been presumed, on the basis of distinctiveness, to be phylogenetically isolated and relatively ancient (> 65 million years old). Using maximum likelihood and parsimony analyses of the rapidly evolving internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA (nrDNA), we show that the cacti are phylogenetically nested among other aridity-adapted lineages of the angiosperm family Portulacaceae. The ITS divergence between pereskioid cacti and the genus Talinum (Portulacaceae) is less than that between many Portulacaceae genera. Synthesis of the ITS data with morphological and chloroplast DNA evidence suggests an origin of cacti in mid-Tertiary, c. 30 million years ago, and a later Tertiary diversification coincident with development of the American desert. This, in tum, implies that the diversification rate in cacti was much higher than in their nearest relatives. The present results illustrate the central role of phylogenetic reconstruction in ecological and evolutionary theory.

Phylogeny of the Caryophyllales Sensu Lato: Revisiting Hypotheses on Pollination Biology and Perianth Differentiation in the Core Caryophyllales

“…Taxa within the portulacaceous cohort have traditionally been treated at the rank of family; however, the degree of paraphyly in Portulacaceae suggests that phylogenetic resolution should be conceptually envisioned as an intrafamilial problem (Hershkovitz and Zimmer 1997). For example, in analyses of ITS, the genetic divergence of Cactaceae from Portulacaceae is equal to or less than that between many pairs of genera in Portulacaceae (Hershkovitz and Zimmer 1997).…”

“…The addition of molecular data has resulted in some clarification. In an analysis of ITS sequences, Hershkovitz and Zimmer (1997) suggested that Cactaceae were embedded within Portulacaceae and sister to Portulaca, Anacampseros, and relatives and portions of Talinum (the ACPT clade, from Anacampseroteae, Cactaceae, Portulaca, and Talinum; Nyffeler 2007). These findings were confirmed and extended by Applequist and Wallace (2001) in an analysis of ndhF sequences; Talinum with Talinella, Portulaca with Anacampseros, and the Cactaceae form three distinct lineages within a well-supported clade.…”

“…Although the monophyly of the ACPT clade seems clear, as summarized by Nyffeler (2007), the pattern of branching within the clade has varied among analyses. Outside of the ACPT clade, Hershkovitz and Zimmer (1997) found that Basellaceae and Didiereaceae form a distinct monophyletic group and are sister to portulacaceous genera Portulacaria and Ceraria. In addition, Applequist and Wallace (2001) described this same clade as consisting of three distinct lineages: Basellaceae; Didiereaceae with Calyptrotheca, Ceraria, and Portulacaria; and a strongly supported assemblage of genera including Claytonia, Montia, Calandrinia, Montiopsis, Cistanthe, Calyptridium, and Phemeranthus.…”

Didiereaceae/Portulacaceae

“…Although Hershkovitz (1993) associated Talinella with Portulacaria and Ceraria, sub sequent molecular studies have clearly shown that it is most closely related to Talinum Adans. (Hershkovitz & Zimmer 1997;Applequist & Wallace 2001). Gynodioecy has, however, also been reported in the monotypic Decaryia Choux, one o f the more basal lineages of the Otherwise dioecious Didiereaceae s.str.…”

“…has been suggested (Rauh & Scholch 1965). Molecular evidence indicates that Ceraria and Portulacaria, as well as the African genus Calyptrotheca Gilg, are more closely related to Didiereaceae than to other Portulacaceae (Hershkovitz & Zimmer 1997;Applequist & Wallace 2000, 2001. The circumscription of Didiereaceae was therefore enlarged to accommodate these three genera (Applequist & Wallace 2003).…”