Systematics Section / ASPT
Griffith, M. Patrick .
Early cactus evolution: a postmodern view.
Early systematic treatments considered the most relictual members of the Cactaceae to be woody broadleaved trees of the genus Pereskia. One treatment in particular (Britton and Rose, 1919) has greatly influenced subsequent work, which advances the widely accepted view that stem-succulence and habit reduction represent derived character states within the Cactaceae, which evolved from a Pereskia-like ancestor; this view may have been culturally influenced. Recent independent phylogenetic papers, although explicitly or implicitly advancing this traditional view, often present evidence that does not support this hypothesis. one subfamily of Cactaceae, the Opuntioideae, is underrepresented in recent work, and is critical to our understanding of early cactus evolution. The current study investigates early-diverging lineages within Cactaceae using phylogenies inferred via Bayesian and parsimony analyses of nuclear (ITS) and chloroplast (trnL-F) DNA sequence data, emphasizing the relationships among the subfamily Opuntioideae, and interprets those results in the context of other phylogenetic work. The following hypotheses are supported: the relationships among the subfamilies of Cactaceae are not clear; the Opuntioideae may be sister to all other cacti; plants of the geophytic, leafless genera Maihueniopsis and Puna are sister to all other opuntioids; geophytism, leaflessness, and architectural simplicity seem plesiomorphic in Opuntioideae. In context with other recent work and the outgroups of the Opuntioideae and Cactaceae, this suggests the possibility that early cacti were not leafy Pereskia-like shrubs, but diminutive geophytes.
1 - Claremont Graduate University, Department of Botany, 1500 North College Avenue, Claremont, California, 91711-3157, USA
Presentation Type: Paper
Location: Cottonwood C (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 3:00 PM