Pollen morphology ofEphedra(Gnetales) and its evolutionary implications

Abstract

The Ephedra lineage can be traced at least to the Early Cretaceous. Its characteristically polyplicate pollen is well-represented in the fossil record and is frequently used as an indicator of paleoclimate. However, despite previous efforts, knowledge about variation and evolution of ephedroid pollen traits is poor. Here, we document pollen morphology of nearly all extant species of Ephedra, using a combination of scanning electron microscopy (SEM) and light microscopy (LM), and reconstruct ancestral states of key pollen traits. Our results indicate that the ancestral Ephedra pollen type has numerous plicae interspaced by unbranched pseudosulci, while the derived pollen type has branched pseudosulci and (generally) fewer plicae. The derived type is inferred to have evolved independently twice, once along the North American stem branch and once along the Asian stem branch. Pollen of the ancestral type is common in Mesozoic fossil records, especially from the Early Cretaceous, but it is less commonly reported from the Cenozoic. The earliest documentation of the derived pollen type is from the latest Cretaceous, after which it increases strongly in abundance during the Paleogene. The results of the present study have implications for the age of crown group Ephedra as well as for understanding evolution of pollination syndromes in the genus.

Palyno‐morphological characteristics of gymnosperm flora of pakistan and its taxonomic implications with LM and SEM methods

“…El‐Ghazaly, Rowley, and Hesse () also reported that polar axis length is much shorter than equatorial diameter. Pseudosulci was observed in different species in the current study is also supported by Bolinder et al (). El‐Ghazaly and Rowley () while investigation of pollen of Ephedra foliata reported similar features and characters as in our results.…”

“…Although he reported a much bigger size of pollens in Taxus wallichiana (equatorial diameter 18 to 28 um and polar length 18 to 20 um) than the current species size. The polyplicate pollens in Ephedra are also reported in previous studies (Bolinder et al, ; Friis, Pedersen, & Crane, ; Hesse et al, ; Ickert‐Bond, ). The Ephedra pollens are usually large as compared to other pollens from 34 to 81 um in equatorial diameter (Bolinder et al, ; Steeves & Barghoorn, ).…”

The middle Miocene palynoflora and palaeoenvironments of Eskihisar (Yatağan basin, south-western Anatolia): a combined LM and SEM investigation

“…Remarks : Ephedra sp. resembles pollen of extant E. nevadensis S. Watson and E. viridis Coville (Steeves & Barghoorn, ; Bolinder et al ., ). In a recent study on extant Ephedra pollen , Bolinder et al .…”

The Gnetales: Recent insights on their morphology, reproductive biology, chromosome numbers, biogeography, and divergence times

“…The pollen of 45 species of Ephedra has been studied with light and scanning electron microscopy (Steeves & Barghoorn, ; Zhang & Xi, ; Ickert‐Bond, ; Ickert‐Bond et al, ; Doores et al, ; Bolinder et al, , ; our Table ). Pollen is ellipsoidal, with characteristic ridges, and rather large (27–58 μm in average equatorial diameter; Figs.…”

“…J, K). Based on a phylogenetic analysis of pollen traits, grains with unbranched valleys in the exine (pseudosulci of Bolinder et al, ; Fig. J) represent the ancestral form, while grains with branched valleys are derived (Fig.…”