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Palynology is the science of palynomorphs, a general term for all entities found in palynological preparations (e.g., pollen, spores, cysts, diatoms). A dominating object of the palynomorph spectrum is the pollen grain. The term palynology was coined by Hyde and Williams (1955; Fig. 1). It is a combination of the Greek verb paluno (пαλύνω, “I strew or sprinkle”), palunein (пαλύνειν, “to strew or sprinkle”), the Greek noun pale (пαλƞ, in the sense of “dust, fine meal,” and very close to the Latin word pollen, meaning “fine flour, dust”), and the Greek noun logos (λογος, “word, speech”).

Pollen is source and transport unit for the male gametes (or their progenitor cell). The unicellular pollen grain represents the microspore of seed plants, the multicellular pollen grain the male gametophytic generation. The development of a pollen grain includes and (Figs. 1 and 2, Gomez et al. 2015; Keijzer and Willemse 1988). Microsporogenesis starts with the differentiation of microspore mother cells (MMC) respectively (PMC). These diploid cells become enclosed by a thick wall and undergo meiosis, forming a tetrad of four haploid , each encased in another callose wall insulating them from each other and from the surrounding diploid tapetal cells (Figs. 1 C-E, and 2). Cytokinesis following meiotic nuclear divisions is accompanied by the formation of cleavage planes determined by the configuration and orientation of the meiotic spindle axes. In the case of , planes are formed after the first and second meiotic divisions leading to the formation of various microspore tetrad types (see “Pollen Morphology and Ultrastructure”). During the cleavage planes are formed simultaneously after the second meiotic division and microspores become arranged in a (Furness and Rudall 1999, 2001).

The study of pollen should encompass all structural and ornamental aspects of the grain. Pollen morphology is studied using LM and SEM and is important to visualize the general features of a pollen grain, including, e.g., symmetry, shape, size, aperture number and location, as well as ornamentation. TEM investigations are used to highlight the stratification and the uniqueness of pollen wall layers as well as cytoplasmic features. The following sections explain the most important structural and sculptural pollen features a palynologist should observe.

The description of pollen ornamentation depends on three major parameters (1) the interpretations of the palynologist (which are subjective), (2) the pollen terminology applied, and (3) the magnification, resolution, and methods used.

For the description of a pollen grain, a number of features are used including size, polarity and shape, aperture condition, ornamentation, and pollen wall structure. Additional and often more specialized features depend on the group of plants under study, Gymnosperms (Cycadales, Ginkgoales, Pinales, Gnetales) vs. Angiosperms (magnoliids, monocots, commelinids, eudicots). These features can only be obtained by the application of a combined analysis with LM, SEM, and TEM (Fig. 1). In order to compare and categorize pollen, a common language and understanding of technical terms is necessary.

Multiple methods and techniques should be used when investigating pollen grains in order to provide comprehensive and accurate information about pollen morphology and ultrastructure (see also “Misinterpretations in Palynology”). The preparation methods used depend on the material to be studied, if the pollen grains are to be obtained from recent flower material (herbarium sheets, newly collected) or from various sedimentary rocks, sediments or soils (fossil to subfossil pollen). Recent and fossil pollen grains are easily studied using both LM and SEM, but recent pollen grains are also more often studied using TEM.

: unit consisting of a single pollen grain

outline: describes the contour of pollen grains in polar and/or equatorial view

angulaperturate: pollen grain with an angular outline where the apertures are located at the angles

areola/areolate: insular ornamentation element