Mesoapertures

Coutinho, A. Pereira, Bandeira, D. Sá da, Currais, L., Soukiazes, E. & Ortiz, S., 2018, Palynotaxonomy of the genus Gladiopappus (Dicomeae, Asteraceae) with special emphasis on the exine ultrastructure and mesoapertures, Blumea 63 (2), pp. 102-108 : 107

Mesoapertures

Our results agree with those described by Tormo-Molina & Ubera-Jiménez (1990, 1995) and Pereira Coutinho et al. (2012) for the Carduoideae and by Pereira Coutinho (2002), Pereira Coutinho & Paiva (2003), Pereira Coutinho & Dinis (2007, 2009), Pereira Coutinho et al. (2011, 2016) and Montes & Murray (2014) for the Asteroideae . Nevertheless, they only partially agree with the data reported by El Ghazaly (1980) and Blackmore (1982) for the Cichorioideae . In fact, these authors considered the mesoaperture as involving, respectively, the outer layer of the endexine and the foot layer, but all our observations indicate that it intersects the foot layer and the upper layer of the endexine. Tellería & Katinas (2009) described the mesoaperture of Mutisia (Mutisioideae) as involving ‘the inner layer of the sexine and the outer layer of the nexine’. Although they employed LM, SEM and TEM, it is not clear which of these techniques they specifically used to observe these structures. Bearing in mind Tellería & Katinas’ (2009) description, we think that they did not observe the details of the apertures with TEM. This implies that, in Mutisia , the columellae, the foot layer and the distal part of the endexine or the columellae and the foot layer are involved in the mesoaperture, in any case a different situation from that we observed in Gladiopappus and other taxa. In the case of Gladiopappus it was relatively easy to observe the mesoapertures limits with LM and SEM , but this is not always the case because, sometimes, they are either diffuse ( Tellería & Katinas 2004) or more or less covered by those of the endoapertures ( Dimon 1971, Tellería & Katinas 2004) or ectoapertures ( Pereira Coutinho & Dinis 2007, 2009). In the last case, the internal view, with SEM , of fractured exines, can reveal the presence of the mesoapertures ( Pereira Coutinho & Dinis 2007), and we suspect that, in some cases, the authors did not observe them because they did not employ TEM or SEM to study the exine ultrastructure and/or the endexine in fractured pollen grains. In conclusion: our data and other authors’ (see Table 2) reveal that the presence of mesoapertures characterizes not only all the most important subfamilies of the Asteraceae ( Asteroideae , Cichorioideae , Carduoideae , Mutisioideae ) but also many of the smaller ones ( Famatinanthoideae , Stifftioideae , Gochnatioideae ), although some varia- tion can occur in the exine layers that are intersected by these pollen structures. It is our conviction that, at least as a trend, the existence of a mesoaperture characterizes the apertural system of the Asteraceae as a synapomorphy, and that future careful examinations with TEM and SEM will reveal its presence in more subfamilies of Asteraceae .