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![LM micrographs of all Sclerosperma pollen types. A-E. Sclerosperma mannii (from Cameroon, coll. van der Burgt, 1958 [K]), same grain in polar and equatorial view. F-J. Sclerosperma profizianum Type A (from DR Congo, coll. Gillet, 279a [WAG]), same grain in polar and equatorial view. K-O. Sclerosperma profizianum, Type B (from Angola, coll. Grobbelaar, s.n. [K]), same grain in polar and equatorial view. P-T. Sclerosperma profizianum, Type C (from Ghana, coll. Hall & Enti, GC 36150 [K]), same grain in polar and equatorial view. U-Y. Sclerosperma profizianum, Type C (from R Congo, coll. Profizi, 841 [K]), same grain in polar and equatorial view. Z-D′. Sclerosperma walkeri (from DR Congo, coll. Leonard, 1614 [BR]), same grain in polar and equatorial view. A, C, F, H, K, M, P, R, U, W, Z, B′. Polar view, high focus. B, D, G, I, L, N, Q, S, V, X, A′, C′. Polar view, optical cross section. E, J, O, T, Y, D′. Equatorial view, upper in high focus and lower in optical cross-section. Scale bars-10 µm.](profile/Fridgeir-Grimsson/publication/329092581/figure/fig1/AS:695352051105796@1542796256408/LM-micrographs-of-all-Sclerosperma-pollen-types-A-E-Sclerosperma-mannii-from-Cameroon.jpg)
LM micrographs of all Sclerosperma pollen types. A-E. Sclerosperma mannii (from Cameroon, coll. van der Burgt, 1958 [K]), same grain in polar and equatorial view. F-J. Sclerosperma profizianum Type A (from DR Congo, coll. Gillet, 279a [WAG]), same grain in polar and equatorial view. K-O. Sclerosperma profizianum, Type B (from Angola, coll. Grobbelaar, s.n. [K]), same grain in polar and equatorial view. P-T. Sclerosperma profizianum, Type C (from Ghana, coll. Hall & Enti, GC 36150 [K]), same grain in polar and equatorial view. U-Y. Sclerosperma profizianum, Type C (from R Congo, coll. Profizi, 841 [K]), same grain in polar and equatorial view. Z-D′. Sclerosperma walkeri (from DR Congo, coll. Leonard, 1614 [BR]), same grain in polar and equatorial view. A, C, F, H, K, M, P, R, U, W, Z, B′. Polar view, high focus. B, D, G, I, L, N, Q, S, V, X, A′, C′. Polar view, optical cross section. E, J, O, T, Y, D′. Equatorial view, upper in high focus and lower in optical cross-section. Scale bars-10 µm.
Source publication
Three currently accepted Sclerosperma species appear to produce four different pollen morphologies. Sclerosperma mannii and S. walkeri pollen share the same distinct reticulate sculpture, but S. profizianum produces three different pollen types (microreticulate, fossulate, and perforate). The pollen morphology suggests that S. mannii and S. walkeri...
Contexts in source publication
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... first LM and SEM micrographs showing pollen of this taxon are by Harley and Hall (1991, plate 4, figures 32 [SEM] and 33 [LM]). The same SEM micrograph is shown in Harley (1999, plate 1, figure 12), and again along with two addi- tional LM micrographs and two attached grains under SEM in Harley (1996, plate 16, figures C and F [SEM], and G and H [LM]). These are all repeated in Harley and Baker (2001, figures 77 and 82 [SEM], 80 and 81 [LM]). ...
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... are all repeated in Harley and Baker (2001, figures 77 and 82 [SEM], 80 and 81 [LM]). A new SEM detail is provided in Harley and Dransfield (2003, figure 11). In total, five or six grains were illustrated using either LM or SEM micrographs, but no TEM micrograph has been presented thus far. ...
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... C (Hall & Enti, GC36150 [K]; Profizi, 841 [K]) ( Figures 1P-Y, 5; Table III) Description. -Pollen, monad, heteropolar, P/E ratio oblate, outline straight-triangular to slightly convex-triangular in polar view, bean-shaped in equatorial view (convex distal face versus concave proximal face); equatorial diameter 37-42 µm in LM, 31-39 µm in SEM, polar axis 10-16 µm in LM; triporate, pori positioned sub-apically on the distal polar face, pori circular to elliptic, 4.0- 6.5 µm in diameter, pori equipped with opercula; exine 1.7-2.5 µm thick in LM, nexine thinner than sexine; pollen wall tectate; sculpture scabrate in LM, perforate, rugulate/verrucate and fossulate in SEM; distal face perforate, perforations elliptic to slit-like, perforations often aligned in sinuous rows, rows of perforations outlining irregular shaped rugulae/ver- rucae (SEM); proximal face perforate and fossulate, perforations elliptic to slit-like, perforations often aligned in sinuous rows, rows of perforations and fossulae outlining irregular shaped rugulae/verrucae, sculpture becoming microrugulate to nanorugulate/ verrucate and perforate towards apices; opercula with nanoverrucate to granulate sublayer and perfo- rate supra-layer (SEM). ...
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... same two SEM micrograph are repeated in Harley and Baker (2001, figures 78 and 79). A single TEM showing the aperture region and operculum is presented in Harley and Drans- field (2003, figure 18). All previously illustrated pol- len grains belonging to this taxon (pollen Type C) were formerly assigned to Sclerosperma mannii (see Table IV). ...
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... previously illustrated pol- len grains belonging to this taxon (pollen Type C) were formerly assigned to Sclerosperma mannii (see Table IV). Figures 1D', 6; Table III) Description. -Pollen, monad, heteropolar, P/E ratio oblate, outline straight-triangular to slightly concave-triangular in polar view, bean-shaped in equatorial view (convex distal face versus concave proximal face); equatorial diameter 35-40 µm in LM, 30-35 µm in SEM, polar axis 15-19 µm in LM; triporate, pori positioned sub-apically on the distal polar face, pori elliptic, 5.0-8.0 µm in dia- meter, pori equipped with opercula; exine 1.7- 2.5 µm thick in LM, nexine thinner than sexine; pollen wall semitectate; sculpture reticulate in LM, reticulate to perforate in SEM; distal face reticulate with broad muri and elliptic to triangular to polygo- nal lumina, 16-25 lumina per 100 µm 2 at central distal face, 0-6 nanogemmae free-standing columel- lae per lumina (SEM); proximal face reticulate to perforate, lumina/perforations elliptic to triangular to polygonal, 0-6 nanogemmae free-standing colu- mellae per lumina; central polar areas and interaper- tural areas reticulate, sculpture becoming microreticulate to perforate towards apices; opercula with nanoverrucate to granulate sublayer and distinct microreticulate supra-layer (SEM). ...
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... -Two LM micrographs showing pollen of this taxon are provided by Sowunmi (1972, plate 3, figure 8 and plate 4, figure 1), but assigned to S. mannii (Table IV). ...
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... LM only, Sclerosperma pollen can be divided into reticulate (including S. manni, S. profizianum Type A, and S. walkeri) and non-reticulate (includ- ing S. profizianum Type B and C; Table III). The reticulate pollen are further divided into coarsely reticulate (including S. mannii and S. walkeri) versus finely reticulate (S. profizianum Type A; compare Figure 1A and 1Z with Figure 1F). Our measure- ments indicate the coarsely reticulate pollen of S. mannii and S. walkeri can be set apart using the length of their polar axis, which is longer in the pollen of S. walkeri (15-19 µm) than in S. mannii (9-15 µm). ...
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... LM only, Sclerosperma pollen can be divided into reticulate (including S. manni, S. profizianum Type A, and S. walkeri) and non-reticulate (includ- ing S. profizianum Type B and C; Table III). The reticulate pollen are further divided into coarsely reticulate (including S. mannii and S. walkeri) versus finely reticulate (S. profizianum Type A; compare Figure 1A and 1Z with Figure 1F). Our measure- ments indicate the coarsely reticulate pollen of S. mannii and S. walkeri can be set apart using the length of their polar axis, which is longer in the pollen of S. walkeri (15-19 µm) than in S. mannii (9-15 µm). ...
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... first LM and SEM micrographs showing pollen of this taxon are by Harley and Hall (1991, plate 4, figures 32 [SEM] and 33 [LM]). The same SEM micrograph is shown in Harley (1999, plate 1, figure 12), and again along with two addi- tional LM micrographs and two attached grains under SEM in Harley (1996, plate 16, figures C and F [SEM], and G and H [LM]). These are all repeated in Harley and Baker (2001, figures 77 and 82 [SEM], 80 and 81 [LM]). ...
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... are all repeated in Harley and Baker (2001, figures 77 and 82 [SEM], 80 and 81 [LM]). A new SEM detail is provided in Harley and Dransfield (2003, figure 11). In total, five or six grains were illustrated using either LM or SEM micrographs, but no TEM micrograph has been presented thus far. ...
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... C (Hall & Enti, GC36150 [K]; Profizi, 841 [K]) ( Figures 1P-Y, 5; Table III) Description. -Pollen, monad, heteropolar, P/E ratio oblate, outline straight-triangular to slightly convex-triangular in polar view, bean-shaped in equatorial view (convex distal face versus concave proximal face); equatorial diameter 37-42 µm in LM, 31-39 µm in SEM, polar axis 10-16 µm in LM; triporate, pori positioned sub-apically on the distal polar face, pori circular to elliptic, 4.0- 6.5 µm in diameter, pori equipped with opercula; exine 1.7-2.5 µm thick in LM, nexine thinner than sexine; pollen wall tectate; sculpture scabrate in LM, perforate, rugulate/verrucate and fossulate in SEM; distal face perforate, perforations elliptic to slit-like, perforations often aligned in sinuous rows, rows of perforations outlining irregular shaped rugulae/ver- rucae (SEM); proximal face perforate and fossulate, perforations elliptic to slit-like, perforations often aligned in sinuous rows, rows of perforations and fossulae outlining irregular shaped rugulae/verrucae, sculpture becoming microrugulate to nanorugulate/ verrucate and perforate towards apices; opercula with nanoverrucate to granulate sublayer and perfo- rate supra-layer (SEM). ...
Context 12
... same two SEM micrograph are repeated in Harley and Baker (2001, figures 78 and 79). A single TEM showing the aperture region and operculum is presented in Harley and Drans- field (2003, figure 18). All previously illustrated pol- len grains belonging to this taxon (pollen Type C) were formerly assigned to Sclerosperma mannii (see Table IV). ...
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... previously illustrated pol- len grains belonging to this taxon (pollen Type C) were formerly assigned to Sclerosperma mannii (see Table IV). Figures 1D', 6; Table III) Description. -Pollen, monad, heteropolar, P/E ratio oblate, outline straight-triangular to slightly concave-triangular in polar view, bean-shaped in equatorial view (convex distal face versus concave proximal face); equatorial diameter 35-40 µm in LM, 30-35 µm in SEM, polar axis 15-19 µm in LM; triporate, pori positioned sub-apically on the distal polar face, pori elliptic, 5.0-8.0 µm in dia- meter, pori equipped with opercula; exine 1.7- 2.5 µm thick in LM, nexine thinner than sexine; pollen wall semitectate; sculpture reticulate in LM, reticulate to perforate in SEM; distal face reticulate with broad muri and elliptic to triangular to polygo- nal lumina, 16-25 lumina per 100 µm 2 at central distal face, 0-6 nanogemmae free-standing columel- lae per lumina (SEM); proximal face reticulate to perforate, lumina/perforations elliptic to triangular to polygonal, 0-6 nanogemmae free-standing colu- mellae per lumina; central polar areas and interaper- tural areas reticulate, sculpture becoming microreticulate to perforate towards apices; opercula with nanoverrucate to granulate sublayer and distinct microreticulate supra-layer (SEM). ...
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... -Two LM micrographs showing pollen of this taxon are provided by Sowunmi (1972, plate 3, figure 8 and plate 4, figure 1), but assigned to S. mannii (Table IV). ...
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... LM only, Sclerosperma pollen can be divided into reticulate (including S. manni, S. profizianum Type A, and S. walkeri) and non-reticulate (includ- ing S. profizianum Type B and C; Table III). The reticulate pollen are further divided into coarsely reticulate (including S. mannii and S. walkeri) versus finely reticulate (S. profizianum Type A; compare Figure 1A and 1Z with Figure 1F). Our measure- ments indicate the coarsely reticulate pollen of S. mannii and S. walkeri can be set apart using the length of their polar axis, which is longer in the pollen of S. walkeri (15-19 µm) than in S. mannii (9-15 µm). ...
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... LM only, Sclerosperma pollen can be divided into reticulate (including S. manni, S. profizianum Type A, and S. walkeri) and non-reticulate (includ- ing S. profizianum Type B and C; Table III). The reticulate pollen are further divided into coarsely reticulate (including S. mannii and S. walkeri) versus finely reticulate (S. profizianum Type A; compare Figure 1A and 1Z with Figure 1F). Our measure- ments indicate the coarsely reticulate pollen of S. mannii and S. walkeri can be set apart using the length of their polar axis, which is longer in the pollen of S. walkeri (15-19 µm) than in S. mannii (9-15 µm). ...
Similar publications
The palm family, Arecaceae, is notoriously depauperate in Africa today, and its evolutionary, paleobiogeographic, and
extinction history there are not well documented by fossils. In this article we report the pollen of two new extinct species of
the small genus, Sclerosperma (Arecoideae), from a late Oligocene (27–28 Ma) stratum exposed along the G...
Citations
... The pollen morphology of Sclerosperma is not only unique within the Arecaceae but within all angiosperms, and its diagnostic features have been pinpointed in numerous publications (e.g., Erdtman and Sing, 1957;Harley and Hall, 1991;Harley, 1996Harley, , 1999Harley, , 2004Harley and Baker, 2001;Harley and Dransfield, 2003;Dransfield et al., 2008). The combined morphological features of extant Sclerosperma pollen observed with light microscopy (LM) and scanning electron microscopy (SEM) were conducted by Grímsson et al. (2019c). The authors showed that the three living Sclerosperma species produce four different pollen morphologies, with S. mannii and S. walkeri sharing a coarsely reticulate pollen and S. profizianum producing three pollen types that are either microreticulate or fossulate or perforate (Grímsson et al., 2019c). ...
... The combined morphological features of extant Sclerosperma pollen observed with light microscopy (LM) and scanning electron microscopy (SEM) were conducted by Grímsson et al. (2019c). The authors showed that the three living Sclerosperma species produce four different pollen morphologies, with S. mannii and S. walkeri sharing a coarsely reticulate pollen and S. profizianum producing three pollen types that are either microreticulate or fossulate or perforate (Grímsson et al., 2019c). Sclerosperma fossil records are rare and comprise only a handful of finds, mostly pollen, depicted from Late Oligocene to Miocene sediments of Africa (Grímsson et al., 2019b;Currano et al., 2020;Ulrich and Grímsson, 2020). ...
... 5I). Compared to extant S. profizianum Type A pollen (Grímsson et al., 2019c), the Dodori MT 1 pollen is more convex-triangular in outline and has a higher number of lumina (41-48 per 100 μm 2 vs. 30-35 per 100 μm 2 ). ...
... Pollen morphological characteristics can provide a reliable basis for classifying and identifying the origin and evolution of plants (Rosenfeldt and Galati 2007;Erik 2012;Baser et al. 2016;Mezzonato-Pires et al. 2018;Reunov et al. 2018;Grimsson et al. 2019;Zhang et al. 2021;Umber et al. 2022). For example, pollen grains of Sclerosperma mannii and S. walheri share the same distinct reticulate sculpture, which suggests that these two currently accepted Sclerosperma species are sister taxa of the same intrageneric lineage (Grimsson et al. 2019). ...
... Pollen morphological characteristics can provide a reliable basis for classifying and identifying the origin and evolution of plants (Rosenfeldt and Galati 2007;Erik 2012;Baser et al. 2016;Mezzonato-Pires et al. 2018;Reunov et al. 2018;Grimsson et al. 2019;Zhang et al. 2021;Umber et al. 2022). For example, pollen grains of Sclerosperma mannii and S. walheri share the same distinct reticulate sculpture, which suggests that these two currently accepted Sclerosperma species are sister taxa of the same intrageneric lineage (Grimsson et al. 2019). Pollen grains from different species have developed unique morphological characteristics during evolutionary while many common morphological features has passed on within families and genera. ...
Background
Plant pollen has diverse morphological characteristics that can be consistently passed down from generation to generation. Information on pollen morphology is thus immensely important for plant classification and identification. In the genus Gossypium , however, in-depth research on pollen morphology is lacking, with only few reports on limited cotton species. To evaluate the diversity of pollen in Gossypium , we therefore conducted a comprehensive analysis of the pollen morphology of 33 cotton species and varieties using scanning electron microscopy.
Results
The 33 analyzed cotton samples exhibited common pollen morphological features, including spherical shapes, radial symmetry, echination, panporation, and operculation, while the pollen size, spine shape, spine density and length showed distinctive features. Pollen size varied significantly among species, with diameters ranging from 62.43 μm in G. harknessii to 103.41 μm in G. barbadense . The exine had an echinate sculptural texture, and spines were mostly conical or sharply conical but occasionally rod-like. Spine density varied from 173 in G. incanum to 54 in G. gossypioides , while spine length ranged from 3.53 μm in G. herbaceum to 9.47 μm in G. barbadense . In addition, the 33 cotton species and varieties were grouped at a genetic distance of 3.83 into three clusters. Cluster I comprised five allotetraploid AD-genome cotton species, four D-genome species, and one K-genome species. Cluster II included 13 diploid species from A, B, D, E, and G genomes, whereas Cluster III only consisted one E-genome species G. incanum .
Conclusions
Although pollen characteristics alone are not enough to resolve taxonomic and systematic relationships within the genus Gossypium , our results add to knowledge on palynomorphology and contribute to phenological information on these taxa. Our findings should aid future systematic and phylogenetic studies of the Gossypium genus.
... Consistent with this pattern and in agreement with highly diverse pollen records from West Africa (Salard-Cheboldaeff and Dejax 1991; Morley 2011; and a summary of these in Couvreur 2015), Pan et al. (2006) reported palms as an important and speciose component of the Chilga floras and noted the extreme paucity of palm fossil occurrences (pollen or otherwise) from the Neogene of Africa. The only record of palms at Mush is pollen and phytoliths of Sclerosperma, a genus that is today restricted to swampy habitats in Central and West Africa (Van Valkenburg et al. 2008;Grímsson et al. 2019;Currano et al. 2020). Today, there are~800 palm species in the Neotropics,~1200 in Southeast Asia, and just 65 on the African continent (Dransfield et al. 2008). ...
... One example shown here (test specimen 2), Figure 3, with micrographs from all three microscopes, is a fossil Sclerosperma pollen (e.g. Grímsson et al. 2019aGrímsson et al. , 2019b from the early Miocene of Ethiopia (Africa). The micrographs comprising this figure were done over a course of four days. ...
An advanced protocol to prepare single extant and fossil pollen grains for transmission electron microscopy (TEM) analysis allows for the fast recovery of data on the ultrastructure of pollen/spores. The protocol is easy to apply and less time consuming than previous methods. The ‘loss’ of pollen grains and pollen that is ‘difficult to locate’ within the embedding material is avoided, and each single pollen grain can be prepared successfully for TEM analysis. This preparation method is meant as an addition to the single-grain method using combined light and scanning electron microscopy to investigate dispersed fossil pollen grains developed by Dr Reinhard Zetter in the late 1980s.
... Moreover, these assemblages are more heterogeneous, containing a significant proportion of palm phytoliths and grass phytoliths that strongly resemble those produced by Arundinoideae and mesophytic (likely C 3 ) Panicoideae species, perhaps growing along the lake margin. Although no palm macrofossils were identified in the census collections, Sclerosperma pollen ( Fig. 4I-K), which is morphologically distinct from other palm genera (Grímsson et al., 2019), was recovered from four stratigraphic levels. Today, Sclerosperma most commonly occurs in swampy areas of West Africa (Van Valkenburg et al., 2008). ...
Miocene paleoecology of East Africa has implications for human origins and understanding the vicariant legacy forests found today on either side of the East African Rift. Fossil leaves preserved in 21.73 million year old lacustrine sediments from the Mush Valley, Ethiopia, provide a unique opportunity to investigate forest composition and dominance-diversity patterns at an ecological scale. We classified and analyzed 2427 leaves in total from two to three quarries within each of six stratigraphic levels, spanning 7 m of section; we estimate each quarry census represents one to three centuries, and 50–60 kyrs separate the oldest and youngest levels. Pollen, phytolith, and compound-specific organic geochemical data were also collected in a detailed stratigraphic context to provide independent, integrated lines of evidence for landscape evolution and lacustrine paleoecology of the system that preserves the macrofossils. Forty-nine leaf morphotypes were documented, and Legume 1 dominated all samples. Nonmetric multidimensional scaling, Jaccard similarity analyses, and diversity and evenness indices demonstrate a degree of change comparable to community ecology dynamics, likely illustrating a dynamic stable state in forest vegetation surrounding the lake. Taxonomic assessments of leaves, phytoliths, and pollen are consistent with a closed canopy forest with limited palm diversity. A high abundance of des-A ring triterpenoid molecules (diagenetic products formed by microbial degradation under anoxic conditions) and very negative δ¹³C values (<−45‰) of several hopanoid compounds point to anoxic conditions at the lake bottom, consistent with exquisite fossil preservation. The proportion of mid-chain n-alkanes is low, signifying relatively few submerged plants, but increases up-section, which signals shallowing of the paleolake. The Mush Valley locality is unique in Africa with regard to its very early Miocene age and the abundance and quality of organic remains. This densely forested landscape in an upland volcanic region of the Ethiopian Plateau showed resilience amid volcanic eruptions and had botanical affinities with species found today in West, Central, and eastern Africa.
... -The outline of this fossil pollen type in both polar and equatorial view, along with its reti- culate sculpture, distally placed apertures and reti- culate opercula, places it firmly within the extant genus Sclerosperma (Table I). Of the four pollen morphologies produced by extant Sclerosperma (see Grímsson et al. 2018), the S. protomannii sp. nov. ...
... -The morphology of this fossil pollen type also clearly places it within Sclerosperma (Table I). Of the four extant pollen types it is most similar to S.profizianum Type A and S.profizianum Type C (see Grímsson et al. 2018), and could be considered an intermediate form between those two extant pollen types. The S. protoprofizianum sp. ...
... Muller (1981), Harley (1996Harley ( , 2004Harley ( , 2006 Most of these affiliations were rejected by Harley and Baker (2001) and Harley (2004Harley ( , 2006). The LM and SEM based pollen morphology of extant Sclerosperma presented by Grímsson et al. (2018) also supports the rejection of any affiliation of these fossil pollen grains with extant Sclerosperma, and excludes all previous fossil pollen accounts except for a single record. The only convincing fossil pollen record of Sclerosperma, prior to this study ( figure 1; plate 3, figures 1 and 2). ...
The palm family, Arecaceae, is notoriously depauperate in Africa today, and its evolutionary, paleobiogeographic, and
extinction history there are not well documented by fossils. In this article we report the pollen of two new extinct species of
the small genus, Sclerosperma (Arecoideae), from a late Oligocene (27–28 Ma) stratum exposed along the Guang River in
Chilga Wereda of north-western Ethiopia. The pollen are triporate, and the two taxa can be distinguished from each other
and from modern species using a combination of light and scanning electron microscopy, which reveals variations in the
finer details of their reticulate to perforate exine sculpture. We also report a palm leaf fragment from a stratum higher in the
same section that is in the Arecoideae subfamily, and most likely belongs to Sclerosperma. The implications of these
discoveries for the evolutionary history of this clade of African arecoid palms is that their diversification was well underway
by the middle to late Oligocene, and they were much more widespread in Africa at that time than they are now, limited to
West and Central Africa. Sclerosperma exhibits ecological conservatism, as today it occurs primarily in swamps and flooded
forests, and the sedimentology of the Guang River deposits at Chilga indicate a heterogeneous landscape with a high water
table. The matrix containing the fossil pollen is lignite, which itself indicates standing water, and a variety of plant
macrofossils from higher in the section have been interpreted as representing moist tropical forest or seasonally inundated
forest communities.
... -The outline of this fossil pollen type in both polar and equatorial view, along with its reti- culate sculpture, distally placed apertures and reti- culate opercula, places it firmly within the extant genus Sclerosperma (Table I). Of the four pollen morphologies produced by extant Sclerosperma (see Grímsson et al. 2018), the S. protomannii sp. nov. ...
... -The morphology of this fossil pollen type also clearly places it within Sclerosperma (Table I). Of the four extant pollen types it is most similar to S.profizianum Type A and S.profizianum Type C (see Grímsson et al. 2018), and could be considered an intermediate form between those two extant pollen types. The S. protoprofizianum sp. ...
... Muller (1981), Harley (1996Harley ( , 2004Harley ( , 2006 Most of these affiliations were rejected by Harley and Baker (2001) and Harley (2004Harley ( , 2006). The LM and SEM based pollen morphology of extant Sclerosperma presented by Grímsson et al. (2018) also supports the rejection of any affiliation of these fossil pollen grains with extant Sclerosperma, and excludes all previous fossil pollen accounts except for a single record. The only convincing fossil pollen record of Sclerosperma, prior to this study ( figure 1; plate 3, figures 1 and 2). ...
The palm family, Arecaceae, is notoriously depauperate in Africa today, and its evolutionary, paleobiogeographic, and
extinction history there are not well documented by fossils. In this article we report the pollen of two new extinct species of
the small genus, Sclerosperma (Arecoideae), from a late Oligocene (27–28 Ma) stratum exposed along the Guang River in
Chilga Wereda of north-western Ethiopia. The pollen are triporate, and the two taxa can be distinguished from each other
and from modern species using a combination of light and scanning electron microscopy, which reveals variations in the
finer details of their reticulate to perforate exine sculpture. We also report a palm leaf fragment from a stratum higher in the
same section that is in the Arecoideae subfamily, and most likely belongs to Sclerosperma. The implications of these
discoveries for the evolutionary history of this clade of African arecoid palms is that their diversification was well underway
by the middle to late Oligocene, and they were much more widespread in Africa at that time than they are now, limited to
West and Central Africa. Sclerosperma exhibits ecological conservatism, as today it occurs primarily in swamps and flooded
forests, and the sedimentology of the Guang River deposits at Chilga indicate a heterogeneous landscape with a high water
table. The matrix containing the fossil pollen is lignite, which itself indicates standing water, and a variety of plant
macrofossils from higher in the section have been interpreted as representing moist tropical forest or seasonally inundated
forest communities.
Background and aims – Pollen grain morphology is an important morphological character for aiding the systematics of flowering plants. For Malpighiaceae, only a single unpublished palynological study has comprehensively sampled ca 60 of this family’s 75 currently accepted genera. To test the systematic relevance of pollen morphology in Amorimia and allies, we characterised the pollen morphology of these lineages. We scored, coded, and mapped 12 characters onto the most recent molecular phylogeny of Amorimia and allies.
Material and methods – We sampled 13 species of Amorimia as ingroup and two species of Mascagnia and Ectopopterys soejartoi as outgroup. Pollen grains were acetolised, characterised, and measured using light microscopy and scanning electron microscopy. Pollen quantitative measurements were submitted to a PCA multivariate analysis. Additionally, quantitative and qualitative characters were scored and coded into 12 characters and mapped onto the molecular phylogeny of Amorimia and allies.
Key results – Amorimia and allies are stenopalynous due to all species showing the same pollen type, with some subtle differences between the pollen grains, such as details of ornamentation, shape, size, and thickness of the pollen exine. However, the patterns of pollen grain evolution showed that few qualitative and apomorphic characters are informative for intrageneric distinction (i.e. type and number of apertures), and almost all quantitative and homoplastic characters analysed were informative at infrageneric levels within Malpighiaceae.
Conclusion – Our results demonstrate that even though the pollen morphology characters of Amorimia and allies show subtle variation, both qualitative and quantitative apomorphic and/or homoplastic characters are highly informative for intra- and infrageneric levels in Malpighiaceae when analysed in a phylogenetic context.
Background
Plants develop a variety of pollen morphological features during long-term evolution, which are controlled by genes and are not easily affected by the external natural environment. Therefore, pollen morphology has great significance in plant taxonomy, evolution and identification. However, there is no detailed study on the pollen morphology of the Gossypium genus although some cotton species have been investigated in the scattered reports. In this study, the pollen morphology of 23 cotton species was comprehensively examined using scanning electron microscopy to evaluate the pollen diversity of the genus and its taxonomic significance.
Results
The common characteristics of Gossypium pollen are spherical, radially symmetrical, echinate, panporate and operculate. The pollen diameter ranges from 62.43µm in G. harknessii to 103.41µm in G. barbadense, revealing that there are great variations in pollen size among cotton species. Moreover, the exine sculpture is echinate. The exine echini shape is mostly conical or sharply conical and occasionally rodlike. Echini density is found maximum in G. incanum (173) and minimum in G.gossypioides (54), meanwhile, echini length varies from 3.53 µm in G. herbaceum to 9.47 µm in G. barbadense. In addition, all cotton species are divided into three clusters based on cluster analysis, which provides new understanding of the evolution and phylogeny of the Gossypium genus.
Conclusion
Although the pollen characteristics alone are insufficient to reconstruct taxonomic and systematic relationships within the genus Gossypium, our findings can enrich our knowledge of sporopollen morphology and fill the phenological gap of these taxa and will contribute to future systematic and phylogenetic studies of the Gossypium genus.
