Abstract Detail

Systematics Section / ASPT

Rydin, Catarina [2], Pedersen, Kaj Raunsgaard [1], Friis, Else Marie [3].

The evolutionary history of Ephedra; evidence from fossils and molecular data.

Molecular studies have shown a very low rate of molecular divergence in Ephedra and it has been suggested that extant Ephedra is young, perhaps not more than 8-32 Myr. Dispersed ephedroid (polyplicate) pollen grains occur in sediments ranging back to more than 200 Myr, but megafossil evidence has so far been rare. Divergence times presented here are based on phylogenetic analysis of five regions from the nuclear and chloroplast genomes. The results indicate that African species are basal within the genus and that most major extant groups originated more than 30 Myr ago. Old World species consist of several well-supported groups. New World species are monophyletic and comprise a North American and a South American clade. New fossils from the Early Cretaceous mesoflora of Buarcos, Portugal, demonstrate that several unique Ephedra characters were present in the Early Cretaceous (Barremian to Aptian). The coalified seeds are small and have two distinct tissues; an inner, membranous integument and an outer envelope of sclerenchymatic cells. The outer envelope often splits into four valves in the apical part, exposing distinct and well-preserved papillae on their inner surface. The papillae are very similar in shape and position to those of recent Ephedra. Polyplicate pollen grains have been observed in situ in the integument tube and maceration of the seeds revealed shed exines in the integument tube. The observations clearly show that these ancient pollen grains germinated in the same way as has been described for recent Ephedra. In conclusion, our fossil evidence and molecular dating document that plants with ephedran reproductive characters were present in the Early Cretaceous and that several extant groups are much older than previously estimated.

1 - University of Aarhus, Department of Geology, Universitetsparken, DK-8000, Aarhus, , Denmark
2 - Stockholm University, Department of Botany, Lilla Frescativägen 5, Stockholm, SE-106, Sweden
3 - Swedish Museum of Natural History, Department of Palaeobotany, Svante Arrhenius väg 7, P.O. Box 50007, Stockholm, SE-104 05, Sweden

Keywords:
divergence times
Ephedra
molecular data
phylogeny
Gnetales
fossils
fossil seeds.

Presentation Type: Paper
Session: 49-2
Location: Cottonwood C (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 11:00 AM
Abstract ID:259