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94 R.L.B. de Borges et al. / Review of Palaeobotany and Palynology 154 (2009) 91–105 Table 3 Characterization of the supratectal processes on the surface of pollen grains of the studied Eriocaulaceae species Species (Micro)Spines Granules diam. (µm) Shape Wall Size (µm) Actinocaphalus Actinocephalus bongardii (A. St.-Hil.) Sano Acute and obtuse Straight and concave 0.38–0.96 0.33–0.36 Actinocephalus cabralensis (Silveira) Sano Acute and obtuse Straight and concave 0.62–0.91 0.40–0.41 Actinocephalus polyanthus (Bong.) Sano Acute and obtuse Straight and concave 0.37–1.05 0.39–0.44 Actinocephalus ramosus (Wikstr.) Sano Acute Straight and concave 0.52–1.09 0.29–0.40 Blastocaulon Blastocaulon albidum Ruhland Acute and obtuse Straight and concave 0.32–0.99 0.21–0.32 Blastocaulon scirpeum (Mart.) Giul. Acute Straight 0.76–0.81 – Eriocaulon Eriocaulon elichrysoides Bong. Obtuse Straight 0.3–0.87 – Eriocaulon humboldtii Kunth Obtuse Straight 0.2–0.7 – Eriocaulon sellowianum Kunth Obtuse Straight 0.2–0.9 – Lachnocaulon Lachnocaulon engleri Ruhland Acute and obtuse Straight 0.53–0.82 0.31–0.39 Lachnocaulon minus Small Acute and obtuse Straight 0.27–0.91 0.27–0.35 Leiothrix Leiothrix subgen. Leiothrix Leiothrix angustifolia (Körn.) Ruhland Acute Straight 0.38–1.35 – Leiothrix hirsuta (Wikstr.) Ruhland Acute Straight 0.78–1.61 – Leiothrix plantago (Mart.) Giul. Acute Straight 0.41–1.07 – Leiothrix rufula (A. St. Hil.) Ruhland Base width and height equal Straight 0.47–1.23 – Leiothrix subgen. Stephanophyllum Leiothrix spiralis (Körn.) Ruhland Acute and obtuse Straight 0.35–0.82 0.22–0.32 Leiothrix vivpara (Bong.) Ruhland Acute Straight 0.38–0.85 – Paepalanthus Paepalanthus subgen. Paepalanthus Paepalanthus myocephalus Mart. ex Körn. Acute and obtuse Straight 0.51–1.02 – Paepalanthus pulchelus Herzog Acute and obtuse Straight 0.62–1.36 0.34–0.35 Paepalanthus pulvinathus N. E. Br. Acute Straight and convex 0.38–1.45 – Paepalanthus sphaerocephalus Ruhland Acute and obtuse Straight and convex 0.36–1.12 0.24–0.29 Paepalanthus subtilis Miq. Acute and obtuse Straight 0.35–0.73 0.31–0.34 Paepalanthus subgen. Platycaulon Paepalanthus planifolius (Bong.) Körn. Acute and obtuse Straight 0.35–2.09 – Paepalanthus subgen. Thelxinöe Paepalanthus leucocephalus Ruhland Acute Straight 0.88–0.96 – Paepalanthus scleranthus Ruhland Acute Straight 0.78–0.89 0.22–0.29 Paepalanthus subgen. Xeractis Paepalanthus comans Silveira Acute and obtuse Straight and convex 0.40–1.32 0.39–0.5 Paepalanthus chrysolepis Silveira Acute and obtuse Straight 0.56–1.97 0.38–0.42 Paepalanthus superbus Ruhland Acute and obtuse Straight and convex 0.45–1.56 0.38–0.49 Philodice Philodice hoffmannseggii Mart. Acute Straight 0.65–0.9 – Rondonanthus Rondonanthus duidae (Gleason) Hensold & Giulietti Acute and obtuse Straight 0.56–1.15 – Syngonanthus Syngonanthus sect. Syngonanthus Syngonanthus arenarius (Gardn.) Ruhland Acute and obtuse Straight 0.36–1.2 – Syngonanthus schwackei Ruhland Acute and obtuse Straight and convex 0.43–0.89 – Syngonanthus verticillatus (Bong.) Ruhland Acute and obtuse Straight and convex 0.56–1.22 – Syngonanthus sect. Carphocephalus Syngonanthus caulescens (Poir.) Ruhland Acute and obtuse Straight 0.55–0.71 – Syngonanthus sect. Eulepis Syngonanthus bisulcatus (Körn.) Ruhland Acute Straight 0.63–1.47 0.38–0.44 Syngonanthus brasiliana Giul. Acute and obtuse Straight and convex 0.32–1.05 – Syngonanthus giuliettiae L. R. Parra Acute and obtuse Straight 0.41–1.42 – Syngonanthus mucugensis Giul. Acute and obtuse Straight and convex 0.45–1.79 0.41–0.47 Syngonanthus sect. Syngonanthus Syngonanthus cipoensis Ruhland Acute and obtuse Straight 0.48–1.26 – Syngonanthus vernonioides (Kunth.) Ruhland Acute and obtuse Straight and convex 0.53–1.74 0.61–0.64 Tonina Tonina fluviatilis Aubl. Acute and obtuse Straight (longitudinally grooved) 0.57–1.37 – In some species of Actinocephalus and Paepalanthus, andinthe genus Eriocaulon, the pollen grains can have more than one furrow and demonstrate different spiral patterns. Species of the genus Eriocaulon have pollen grains with 2–3 apertures (Plate I, 1–2), arranged in a characteristic pattern. In these pollen grains, interapertural exines are generally visible under LM, arranged in a two-
y-two formation in different plans as in a crosshatch pattern (Plate I, 1–2). In the genus Actinocephalus, A. bongardii, and A. denudatus, have pollen grains with a furrow in a single spiral pattern, but A. divaricatus and A. ramosus have two spirals in varied patterns (Plate I,10–12). The pollen grains of Paepalanthus have apertures that generally trace a single spiral (Plate IV,7–9), but do show significant variation in the number of spirals, while the genus Philodice has grains with various types of apertures in spiral form but no one predominant type (Plate V, 2–10). Among the species of Syngonanthus studied, pollen grains could be 2-zonasulcate (Plate VI, 7–9) or could have spiral apertures in various arrangements (Plate VII, 2–4). The interapertural exines are of varying widths, with the narrowest seen in Blastocaulon (~7 µm) and in Eriocaulon (~8 µm), while the widest strips were noted in Syngonanthus (up to 17 µm). The greater number of studied taxa has unornamented apertural membranes, except for the pollen grains of Eriocaulon and Syngonanthus arenarius. Eriocaulon are ornamented with obtuse microspines on this membrane (Plate I, 5), whereas the pollen grains of Syngonanthus arenarius have spines and microspines on the furrow membrane (Plate VII, 1). At the apertures of the pollen grains of Rondonanthus, the apertural membranes are not ornamented (Plate VI, 6), as is the case in Actinocephalus (Plate II, 5), Blastocaulon (Plate II, 11), Lachnocaulon (Plate III, 4), Leiothrix (Plate IV, 3), Paepalanthus (Plate V, 1) and Philodice (Plate V, 11). 3.3. Exine — structure and ectexine ornamentation The exine is usually thin, varying in thickness from 1 to 3 µm. The thickest exine was observed in specimens of the genera Eriocaulon and Rondonanthus, whose average exine thickness is 2 µm; in the other genera, the average exine thickness is 1 µm (Table 2). The layer stratification of the exine is discernible, with the nexine being thicker than the sexine in Eriocaulon and some species of Syngonanthus. The exine is undifferentiated in Leiothrix spp., showing no individualization of the layers under LM, with the exception of L. flavescens and L. plantago, whose sexine and nexine are quite distinct. The same is observed in Blastocaulon albidum. In Paepalanthus, the exine stratification can be either undifferentiated or differentiated into sexine and nexine and, in the latter case, the analyses show that the exine can have a thicker sexine, or that the sexine and nexine could be of equal thickness. Due to the thinness of the exine in the pollen grains of the majority of the species analysed, the exine layers (sexine and nexine) were not measured individually, although this does not prevent a qualitative analysis of the relative thicknesses of the two layers (Table 4). The ectexine surface is irregular (Plate III, 10–11), sometimes presenting areas with microperforations (Plate II, 2;Plate IV, 3)or being slightly microrugulate (Plate III,5–6,10; Plate V,1;Plate VI,11–12). The ectexine surface has two morphological types of supratectal processes: granulose and (micro)spinose (the latter have tapered apices). Due to their small size, both types are more easily visualized under SEM. In spite of the heterogeneity in their size, the granules appear to be more uniform than the microspines. The granules vary in diameter from 0.22 to 0.64 µm and are present in the majority of the genera studied. They are generally distributed among the microspines and along the edge of the interaperture exine strip in Actinocephalus (Plate II, 6),Lachnocaulon (Plate III, 5),Paepalanthus and Syngonanthus (Plate VII, 6). They were not observed in Eriocaulon, Philodice or Tonina. The (micro)spines show a wide range of variation in size, being between 0.2 and 2.09 µm in length, with a majority being acute (Plate II, 5; Plate III, 11;Plate V, 12) while others are more obtuse (Plate I, 5; Plate V,1;Plate VII, 1). The acute or obtuse shape is related to the size of the supratectal processes, with the larger processes (spines) generally being acute (Plate II, 5; Plate III, 11), while the smaller processes (microspines) are generally obtuse (although some are occasionally R.L.B. de Borges et al. / Review of Palaeobotany and Palynology 154 (2009) 91–105 acute) (Plate I,5;Plate VI,12;Plate VII, 1). The largest spinose processes are observed in Paepalanthus chrysolepis and P. planifolius (Table 3). 4. Discussion 4.1. Pollen morphological considerations The pollen grains in Eriocaulaceae present few variations with regard to size or shape, being small to medium and mainly spheroidal. Large variations in the size of the pollen grains at the intra-specific level were seen among the specimens studied, which could be attributed to the different degrees of maturation of the pollen grains derived from different flowers on the same inflorescence. Giulietti (1996), for example, reported that the maturation of the flowers in the inflorescences of the genus Leiothrix is centripetal, a condition that has been seen in the entire family. Coan et al. (2007a) pointed out that flowers of many different ages occur on the same inflorescence in Syngonanthus caulescens. The sulcate feature, colpate according to some authors (Furness, 1988; Rull, 2003), the typical apertural pattern of the family, was observed in all species included here. Thanikaimoni (1965) described several apertural arrangements for pollen grains of the Eriocaulon species, and the patterns seen here are very similar to those described by that author. Apertures having a design resembling the pattern on a tennis ball are quite unique, and are described here for the genera Leiothrix and Lachnocaulon, although Thanikaimoni (1965) also observed this apertural type in two different genera, Syngonanthus and Tonina, as well as a very similar pattern in the pollen grains of Lachnocaulon. The genera Actinocephalus, Blastocaulon, and Paepalanthus have very similar aperture patterns, with apertures in a single spiral (helicoidal) or tracing various designs. However, the pollen4 grains of all species of Syngonanthus sect. Eulepis and of S. imbricatus [S. sect. Thysanocephalus after Ruhland (1903) and S. sect Eulepis after Lazzari (2000)] have a 2-zonasulcate apertural pattern — the first time this pattern has been reported for this family. On many occasions, even under SEM, it is difficult to distinguish between supratectal processes to determine which are microspines and which are, in fact, granules (Plate I,6;Plate II,2;Plate III,6;Plate IV, 12). The following species have pollen grains that were entirely microspinose: Actinocephalus cabralensis, Blastocaulon scirpeum, Lachnocaulon engleri, Paepalanthus leucocephalus and P. subtilis. All of the other taxa have exines that varied from microspinose to spinose, with acute spines and acute to obtuse microspines, with the exception of the species of Leiothrix that had both acute spines and microspines. The morphology of the grooved spines of Tonina fluviatilis, unique in the family, was very similar to those described by Halbritter et al. (2007) for Thymelaea passerina (L.) Coss. & Germ. (Thymelaeaceae). The representatives of Eriocaulon, the basal group of the family according to M. J. G. Andrade (unpubl. data.), generally have three apertures and a large apertural area. The number of apertures diminishes and the interapertural exine strips are wider among the genera of the subfamily Paepalanthoideae, which indicates a decrease in the apertural area. In the genus Syngonanthus, a significant decrease in the apertural area has been noted, mainly in the species of S. sect. Eulepis, and in S. imbricatus, which have zonasulcate apertures and, consequently, have smaller apertural areas than the others. 4.2. Taxonomic considerations The contribution of pollen morphological characteristics to taxonomic studies of the Eriocaulaceae can be seen at many levels. Although the family can be considered stenopalynous, as recorded by Erdtman (1943, 1952), Thanikaimoni (1965), andSantos et al. (2000), the pollen characteristics presented here suggest that they have taxonomic value. The pollen characteristics of the Eriocaulaceae are sufficient to distinguish them from the other families of the order Poales. 95
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