The age of major monocot groups inferred from 800+rbcL sequences

Abstract

Phylogenetic research on monocots has been extraordinarily active over the past years. With the familial interrelationships being sufficiently understood, the question of divergence times and crown node ages of major lineages comes into focus. In this study we present the first attempt to estimate crown and stem node ages for most orders and families of monocots, based on rbcL sequence data and comprehensive taxon sampling. From our analysis it is obvious that considerable monocot diversification took place during the Early Cretaceous, with most families already present at the Cretaceous-Tertiary boundary. Araceae, Arecaceae and Orchidaceae are among the oldest families with crown node ages reaching back into the Early Cretaceous. We comment on possible error sources and the necessity for methodological improvement in molecular dating.

Phylogeny and biogeographic diversification of Maianthemum (Ruscaceae: Polygonatae)

“…This result is in agreement with Good-Avila et al (2006) based on rbcL and trnL-F data and have been adopted by Janssen and Bremer (2004). We, thus, calibrated the crown age of monocots as 134 mya in our analyses.…”

“…The oldest Asparagales fossil is 37.5 mya (Couper, 1960;Muller, 1981) and the estimate was 60-69 mya in Good-Avila et al (2006). In our estimates, however, the Asparagales was treated considerably older and was constrained at 119 mya based on Janssen and Bremer (2004). Similarly, the Liliales has the oldest fossil at about 45.15 mya (Sun and Dilcher, 1988;Herendeen and Crane, 1995), whereas our estimate was 85.70 mya.…”

“…A few fossils ACCEPTED MANUSCRIPT of the Asparagales have been reported from the late Eocene (Couper, 1960;Muller, 1981;Herendeen and Crane, 1995), but all need to be carefully re-examined as they may be too young to calibrate the crown clade of the order (Wikström et al, 2001;Janssen and Bremer, 2004). The age of the crown Asparagales was estimated as 92-101 mya by Wikström et al (2001), and 119 mya by Janssen and Bremer (2004). Due to the criticisms over the estimates of the former (e.g., Bremer, 2002;Chase, 2004), we set the minimum crown age of the order at 119 mya based on the oldest age of the order.…”

“…Convergence of the chains was checked using the program Relatively few reliable fossils have been reported from the monocots primarily due to problems of preservation (Herendeen and Crane, 1995;Gandolfo et al, 2000;Crepet et al, 2004). A few fossils ACCEPTED MANUSCRIPT of the Asparagales have been reported from the late Eocene (Couper, 1960;Muller, 1981;Herendeen and Crane, 1995), but all need to be carefully re-examined as they may be too young to calibrate the crown clade of the order (Wikström et al, 2001;Janssen and Bremer, 2004) …”

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“…Traditionally, the species taxonomy and cultivars identification of the genus Cymbidium was entirely based on morphological traits which is al., 2007) to as much as ~110 Ma (Janssen and Bremer, 2004). A correct time estimation is essential for our understanding of the mechanisms underlying the diversification of orchids, and Cymbidium could significantly contribute towards evolutionary studies owing to its genetic diversity -such as significant increases in speciation rates that may temporally correlate to climatic changes, tectonic events, or radiation of pollinators etc.…”