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Quartz–tourmaline orbicules are unevenly distributed in the roof segment of the Land's End granite, SW England. This study shows that the orbicules formed from an immiscible hydrous borosilicate melt produced during the late stages of crystallization, and differentiates tourmaline formed by dominantly magmatic and dominantly hydrothermal processes. Trace elements and boron isotope fractionation can be tracked in tourmaline, and create a timeline for crystallization. Tourmaline from the granite matrix has higher V, Cr and Mg content and is isotopically heavier than the later crystallizing inner orbicule tourmaline. Overgrowths of blue tourmaline, occurring together with quartz showing hydrothermal cathodoluminescence textures, crystallized from an aqueous fluid during the very last crystallization, and are significantly higher in Sr and Sn, and isotopically heavier. Tourmaline associated with Sn mineralization is also high in Sr and Sn, but has boron isotopic compositions close to that of the magmatic tourmaline, and is not formed by the same fluids responsible for the blue overgrowths. The ore-forming fluids precipitating tourmaline and cassiterite are likely derived from the same magma source as the granite, but exsolved deeper in the magma chamber, and at a later stage than orbicule formation. Tourmaline from massive quartz–tourmaline rocks is concentrically zoned, with major and trace element compositions indicating crystallization from a similar melt as for the orbicules, but shows a more evolved signature.

Distinctive magmatic-hydrothermal, tourmaline-rich features have developed in the Heemskirk and Pieman Heads granites from western Tasmania, Australia. They are categorized as tourmaline-rich patches, orbicules, cavities, and veins, based on their distinctive morphologies, sizes, mineral assemblages, and contact relationships with host granites. These textural features occur in discrete layers in the roof zone of granitic sills within the Heemskirk and Pieman Heads granites. Tourmaline patches commonly occur below a tourmaline orbicule-rich granitic sill. Tourmaline-filled cavities have typically developed above the tourmaline-quartz orbicules in the upper layer of the white phase of the Heemskirk Granite. Tourmaline-quartz veins penetrate all exposed levels of the granites, locally cutting tourmaline orbicules and cavities.The tourmalines are mostly schorl (Fe-rich) and foitite, with an average end-member component of schorl45 dravite6 tsilaisite1 uvite0 Fe-uvite3 foitite31 Mg-foitite4 olenite10 Element substitutions of the tourmalines are controlled by FeMg-1, YAlX∎(R2+Na)-1, and minor YAlO(R2+OH)-1 (where R2+ = Fe2+ + Mg2+ + Mn2+) exchange vectors. Several trace elements in tourmaline have consistent chemical evolutions grouped from tourmaline patches, through orbicules and cavities, to veins. There is a progressive decrease of most transition and large ion lithophile elements, and a gradual increase of most high-field strength elements. These compositional variations in the different tourmaline-rich features probably relate to element partitioning occurring in these phases due to volatile exsolution and fluxing of aqueous boron-rich fluids that separated from the granitic melts during the emplacement of S-type magmas into the shallow crust (4 to 5.5 km).Tourmalines from the Heemskirk Granite are enriched in Fe, Na, Li, Be, Sn, Ta, Nb, Zr, Hf, Th, and rare earth elements relative to the tourmalines from the Pieman Heads Granite, but depleted in Mg, Mn, Sc, V, Co, Ni, Pb, Sr, and most transition elements. These results imply that bulk compositions of the host granites exert a major control on the chemical variations of tourmalines. The trace element compositions of tourmalines from the Sn-mineralized Heemskirk Granite are different from those of the barren Pieman Heads Granite. Trace element ratios (e.g., Zn/Nb, Co/Nb, Sr/Ta, and Co/La) and Sn concentrations in tourmaline can distinguish the productive Heemskirk Granite from the barren Pieman Heads Granite.

Garcinia dulcis (Roxb.) Kurz (Clusiaceae) is a medicinal plant native to Southeastern Asia, with a peculiar, precocious pollenkitt production in early microspore development. We aimed to find out whether different secretory activities of the tapetum or a premature sporoderm development provides additional evidence for our recent hypothesis for the precocious pollenkitt production. Histology, histochemistry and ultrastructure of tapetum and sporoderm development during pollenkitt secretion in Garcinia dulcis were conducted, based on light and electron microscopy analysis. The results showed that Garcinia dulcis possesses normal pollen development. The presence of two different pollen coating types, precocious pollenkitt (L1) and common pollenkitt (L2), in the anther tapetum indicate that they are produced in two different active stages of the secretory tapetum. The precocious pollenkitt production and transport to the locule takes place in early active tapetal cells at early tetrad to early microspore stage and is ongoing until late microspore stage. The production of the second type of pollenkitt (L2) starts shortly after the first active tapetum stage together with the formation of sporopollenin precursors. The sporoderm formation was completed at late microspore stage, when the tapetal cell walls start to disintegrate. Orbicules are lining the inner tapetum wall at middle to late microspore stage. ER (during early microspore stage) and plastids (during late microspore stage) were the two main sources of pollenkitt, which finally fused to pollenkitt droplets when the tapetal cells degenerated at mature bicellular pollen stage.

Orbicules are granules of sporopollenin or polymorphic sporopollenin-elements produced by the tapetum, associated with pollen grains and tapetum cells. In angiosperms, they are common in the ANA grade and monocots, but are absent in late-branching clades such as the majority of Asteraceae and the majority of Lamiaceae, revealing an evolutionary trend from presence to absence along the phylogenetic tree. However, for several orders of angiosperms, no data on orbicules is available. We investigated orbicules in 34 species from 29 different genera and 14 orders, for which limited or no data was available (Acorales, Arecales, Buxales, Celastrales, Crossosomatales, Dilleniales, Escalloniales, Fagales, Garryales, Gunnerales, Paracryphiales, Santalales, Trochodendrales, Zygophyllales). We photographed pollen sacs and pollen grains with a SEM, then described selected orbicule traits and measured their size. We then calculated: (1) the phylogenetic signals for (a) orbicule size in a selected group of species and (b) presence/absence of orbicules in all angiosperm groups until now recorded in the literature; (2) the ancestral state of orbicule size; (3) origin, loss and transition rate for presence/absence of orbicules in angiosperms. Orbicule traits are supported both by a strong phylogenetic signal and by a significant evolutionary trait value. The evolutionary rate for the presence of orbicules confirms that it is a plesiomorphic trait showing adaptive radiation with a significant increase in origins and diversification, while the phylogenetic signal for size of the orbicules indicates evolutionary convergence. Furthermore, we detected an evolutionary trend towards a reduction in the size of orbicules, that might have led to their absence in most late-branching clades.

Tourmaline is widespread in metapelites and pegmatites from the Neoproterozoic Damara Belt, which form the basement and potential source rocks of the Cretaceous Erongo granite. This study traces the B-isotope variations in tourmalines from the basement, from the Erongo granite and from its hydrothermal stage. Tourmalines from the basement are alkali-deficient schorl-dravites, with B-isotope ratios typical for continental crust (δ 11 B average −8.4‰ ± 1.4, n  = 11; one sample at −13‰, n  = 2). Virtually all tourmaline in the Erongo granite occurs in distinctive tourmaline-quartz orbicules. This “main-stage” tourmaline is alkali-deficient schorl (20–30% X-site vacancy, Fe/(Fe + Mg) 0.8–1), with uniform B-isotope compositions (δ 11 B −8.7‰ ± 1.5, n  = 49) that are indistinguishable from the basement average, suggesting that boron was derived from anatexis of the local basement rocks with no significant shift in isotopic composition. Secondary, hydrothermal tourmaline in the granite has a bimodal B-isotope distribution with one peak at about −9‰, like the main-stage tourmaline, and a second at −2‰. We propose that the tourmaline-rich orbicules formed late in the crystallization history from an immiscible Na–B–Fe-rich hydrous melt. The massive precipitation of orbicular tourmaline nearly exhausted the melt in boron and the shift of δ 11 B to −2‰ in secondary tourmaline can be explained by Rayleigh fractionation after about 90% B-depletion in the residual fluid.

Pollen morphology of 19 taxa in Persicaria section Cephalophilon and four related taxa in the genus Koenigia was examined. Pollen grains shed as a monad were oblate to subprolate in shape (P/E = 0.50–1.20), small to large in size (13.44–51.16 µm), and tricolpate, octocolpate, or pantoporate. Three types of exine ornamentation were identified: (I) reticulate (P. sect. Cephalophilon), (II) reticulate with microechinae (Koenigia delicatula), and (III) microechinate (studied taxa of Koenigia except K. delicatula). The quantitative pollen characteristics analyzed using principal component analysis showed diagnostic importance among the taxa. The comprehensive consideration of pollen characteristics (aperture type, pollen size, and detailed exine ornamentation) is systematically informative, particularly at the series level of P. sect. Cephalophilon. Furthermore, the results also support the separation of some taxa of uncertain taxonomic affinities between Koenigia and P. sect. Cephalophilon. Orbicules were absent in all taxa of P. sect. Cephalophilon but were consistently found in Koenigia. The examined orbicules were spherical with a psilate surface, and the studied orbicule characteristics provided additional evidence to clarify the taxonomic position of some taxa of Koenigia. The orbicule and pollen morphology, especially aperture types, has proven to be a useful diagnostic characteristic in P. sect. Cephalophilon and related taxa, and their systematic importance is further discussed in this study.

Next to pollen, stamens of flowering plants often produce microstructures, called orbicules, lining the locules. Although the existence of orbicules has been known since 1865, their function still remains enigmatic. This paper surveys orbicule distribution throughout angiosperms, including +1,500 entries. We show that orbicules are found all over of flowering plants with an evolutionary trend towards orbicule absence in more derived clades. Orbicules are common in the ANITA-grade and 85 % of the monocots studied produce orbicules, with Orchidaceae, Commelinales and Zingiberales as notable exceptions. Within eudicots, asterids are most densely sampled with 61 % orbicule presence. Asteraceae and the majority of Lamiaceae lack orbicules. For 17 angiosperm orders orbicule distribution data are lacking entirely. We demonstrate that the hypothesized correlation of orbicule presence with non-amoeboid tapetum types holds true. The presence of orbicules is therefore a convenient proxy for tapetum characterization. The potential of orbicules as an a-cellular model system for patterned sporopollenin polymerization is discussed and suitable model plants for future functional orbicule-research are identified.

Different processes have been proposed to explain the variety of igneous layering in plutonic rocks. To constrain the mechanisms of emplacement and crystallization of ascending magma batches in shallow plutons, we have studied comb layers and orbicules from the Fisher Lake Pluton, Northern Sierra Nevada. Through a detailed study of the mineralogy and bulk chemistry of 70 individual layers, we show that comb layers and orbicule rims show no evidence of forming through a self-organizing, oscillatory crystallization process, but represent crystallization fronts resulting from in situ crystallization and extraction of evolved melt fractions during decompression-driven crystallization, forming a plagioclase-dominated cres-cumulate at the mm- to m-scale. We propose that the crystal content of the melt and the dynamics of the magmatic system control the mechanisms responsible for vertical igneous layering in shallow reservoirs. As comb layers crystallize on wall rocks, the higher thermal gradients will increase the diversity of comb layering, expressed by inefficient melt extraction, thereby forming amphibole comb layers and trapped apatite + quartz saturated evolved melt fractions. High-An plagioclase (An 90 –An 97.5 ) is a widespread phase in Fisher lake comb layers and orbicule rims. We show that a combination of cooling rate, latent heat of crystallization and pressure variations may account for high-An plagioclase in shallow melt extraction zones.

Variations in pollen characters and tapetum behavior were recently acknowledged in the early-divergent family Nymphaeaceae and even within the genus Nymphaea , which probably is not monophyletic; some traits such as infratectum and tapetum type are also a matter of different interpretations. In this study, developmental characters of the pollen grains and tapetum in Nymphaea subgenus Hydrocallis are provided for the first time. Observations were made in N. amazonum , N. gardneriana , and N. prolifera using light, scanning, and transmission electron microscopy. Tapetum is of the secretory type and produces orbicules. At microspore and pollen grain stages, the distal and proximal walls differ considerably. This result supports the operculate condition of the aperture in Hydrocallis , and such aperture might be plesiomorphic for Nymphaeoideae. The infratectum is intermediate, composed of inter-columellae granular elements, robust columellae consisting of agglomerated granules, complete columellae, and fused columellae. Narrow microchannels are present and persist until the mature pollen grain stage. The membranous granular layer is often present in the pollen grains of Nymphaeaceae. In N. gardneriana , this layer is most probably a component of the intine because it is lost after acetolysis. Orbicules in the Nymphaeaceae are characterized as spherical or subspherical, with a smooth sporopolleninic wall that surrounds an electron-lucent core and with individual orbicules that usually merge to give irregular aggregations. The aperture, pollen wall ultrastructure, and the tapetum of the studied species are discussed in an evolutionary and systematic context, and these characters are also compared with those of other angiosperm lineages.

Microsporogenesis, microgametogenesis, and anther structure of 14 species belonging to Rhamneae (Rhamnoids clade), Paliureae, Pomaderreae, Colletieae, and Gouanieae (Ziziphoids clade) of the Rhamnaceae family were analyzed using bright-field, scanning, and transmission electron microscopy. The aim is to look for morphological characters that have systematic value on a suprageneric level within the family. The character states of the number of nuclei in tapetai cells, the endothecial thickening pattern, and the number of endothecial layers are consistent on tribal level. Tribes were previously delineated based on molecular phylogenetic evidence. On the other hand, pollen morphology does not seem to have systematic value at tribal level in Rhamnaceae. The presence or absence of orbicules and their morphology vary within tribes. It seems that for Rhamnaceae, the anatomy of the reproductive sporophytic structures could have more systematic value than the gametophytic structures. However, more studies are needed to confirm this.