Grass pollen surface ornamentation: a review of morphotypes and taxonomic utility

Luke Mander,Surangi W Punyasena

doi:10.1144/jmpaleo2015-025

Abstract

The classification of grass pollen is a classic problem in palynology. One approach to this problem is to image grass pollen using scanning electron microscopy (SEM) and to construct morphotypes on the basis of surface ornamentation patterns. In this paper, we construct a database of published SEM images of grass pollen surface ornamentation and use this database to review the status and utility of grass pollen morphotypes. Very little SEM data on grass pollen surface ornamentation have been collected. There are more SEM data on the pollen of species from larger subfamilies such as the Pooideae, but there are no SEM data on the pollen of relatively small subfamilies or the early-diverging APP clade of grasses. The available data support the following six morphotypes: the Hordeum -type, Triticum -type, Avena -type, Setaria -type, Pariana -type and Stipa -type. The phylogenetic distribution of these morphotypes cannot be assessed reliably with the available data, but the Pariana and Stipa types are apparently restricted to the BEP clade. We suggest that fossil grass pollen grains could be classified using these morphotypes and that this could be a means of generating useful evolutionary and palaeoecological information from the grass pollen fossil record. Supplementary material: Our database of grass pollen surface ornamentation is available at https://doi.org/10.6084/m9.figshare.c.2134356

Highlights

We focus our attention on grass pollen morphotypes (e.g. Köhler & Lange 1979) and aim to investigate the following questions: (1) how much scanning electron microscopy (SEM) data have been collected on grass pollen surface ornamentation? (2) How are the grass pollen morphotypes distributed among the subfamilies of Poaceae?
Extremely limited (only 6 of the 1462 species contained within the Bambusoideae subfamily are present in our database, for example (Fig. 3)), this raises the possibility that a simple morphotyping approach based on SEM images of surface ornamentation might be used to distinguish the BEP clade and the Bambusoideae subfamily in the fossil record and in samples of modern material
Though, that the spread of morphotypes across the Poaceae phylogeny suggests that this role is likely to be restricted to the generation of raw diversity counts, which could be used to track diversification history and compositional change through time

Summary

Database construction

We searched the literature and constructed a database of published SEM images of grass pollen surface ornamentation. The Triticum-type ‘is characterised by small [areolae] bearing only one to three, rarely more, spinules’ The Setaria-type ‘is characterised by extensive field-like [areolae] of irregularly polygonal outlines. Their bulging surface is studded with very small pointed spinules’ The term ‘areolae’ replaces ‘insulae’, following Punt et al (2007) To these four established morphotypes we add the Pariana-type and the Stipa-type.

SEM data and the taxonomic utility of grass pollen morphotypes

Spartina townsendii Spartina pectinata Triodia basedowii

Findings

Future work