Terms derived from LM level cannot always be extended and applied to SEM level

A classical example: Ulmus pollen at LM level was described as rugulate (rugulae: elongated exine elements longer than 1 |_im; irregularly arranged). In low SEM magnifications the term verrucate (verrucae:

wart-like element more than 1 pm, broader than high) would describe the ornamentation in a better manner. High SEM magnifications show additional granules (structure or sculpture elements of different size and shape; smaller than 1 pm). A typical rugulate ornamentation at SEM level is present in, e.g., Sanicula, which is quite dissimilar to the ornamentation seen in Ulmus at SEM high resolution level.

This is a good place to mention interpretative pitfalls. The denotation of ornamentation frequently depends on the optical magnification used and particularly on the point resolution. Very many (paleo-)paly-nologists have relied on LM only. Even low-powerSEM may not be sufficient to distinguish pollen grains unequivocally which are in LM very similar (for examples and discussion see FERGUSON et al. 2007).

Ornamentation in LM and SEM view left: rugulate (LM) right: verrucate (SEM)

left:

Ulmus laevis Ulmaceae surface detail verrucate, granulate right:

Sanicula europaea Apiaceae surface detail rugulate

Ornamentation in LM and SEM view left: rugulate (LM) right: verrucate (SEM)

left:

Ulmus laevis Ulmaceae surface detail verrucate, granulate right:

Sanicula europaea Apiaceae surface detail rugulate

A second example is scabrate, a term used for light microscopy only, describing minute sculpture elements of undefined shape and of a size close to the resolution limit of the light microscope. As an example, Juglans pollen is scabrate in LM and (with some reservation) under low power SEM, but microechinate at high resolution SEM.

Ornamentation in LM and SEM view

Juglans sp. Juglandaceae polar view scabrate to psilate (LM)

microechinate (SEM)

Ornamentation in LM and SEM view

Juglans sp. Juglandaceae polar view scabrate to psilate (LM)

microechinate (SEM)

Another example for different interpretations in LM and SEM is the term psilate. Many pollen grains are psilate in LM view, but show a distinct ornamentation at SEM level. For example, in LM view pollen of Allium is psilate (see "Illustrated Glossary" - psilate), in SEM view it is striate and perforate (see "Pollen Morphology").

The term granulate (describing minute sculptural elements of undefined shape and of a size close to the resolution limit of the LM) is adequate for features at low SEM magnification. At significantly higher resolution a more adequate description is often possible. The actual shape of such

"granules" depends on the much better resolution of details at high SEM magnification, where a "granulate ornamentation" emerges as, for example, a great number of very small spines (microechini), the pointed ends seen best in profile, not from top view. The allegedly granulate ornamentation of many Poaceae is in fact microechinate; see "Illustrated Glossary".

Another interpretative pitfall does not depend on optical magnification. Ornamentation sometimes depends entirely or to a high degree on the preparation method. A striking example is the presence or complete absence of distinct echini on pollen of many Araceae/Aroideae: fresh or dry material exhibits a distinct echinate ornamentation, whereas after acetolysis the echini are completely removed. These echini are composed of polysaccharides (singular exception) and lack sporopollenin completely. The pollen is then - correctly -called psilate (WEBER et al. 1999).

An example for different possible interpretations in relation with a differing degree of hydration is Trichosanthes anguina (Cucurbitaceae), where the ornamentation reflects the differing degree of hydration. The overview micrograph on the left shows a fully turgescent pollen, and on the right a less turgescent one. The ornamentation can be described as either areolate, or ver-rucate or even fossulate. Perforations are clearly visible in fully turgescent pollen only. So ornamentation should better be called verrucate and perforate.

Hydration

Trichosanthes anguina Cucurbitaceae pollen grains of different state of hydration

Hydration

Trichosanthes anguina Cucurbitaceae pollen grains of different state of hydration

Hydration

Trichosanthes anguina

Cucurbitaceae left: surface detail areolate right: surface detail verrucate, perforate

Hydration

Trichosanthes anguina

Cucurbitaceae left: surface detail areolate right: surface detail verrucate, perforate

A specific ornamentation sometimes even depends on peculiarities during pollen development. Ubisch bodies are usually found as isolated particles between pollen grains, or lining the mature locular wall (HUYSMANS et al. 1998, HALBRITTER and HESSE 2005, VINCKIER et al. 2005; equivalents are found in ferns: LUGARDON 1981). Pollen grains of Cupressaceae and Taxaceae are often equipped with adhering (adnate) Ubisch bodies, which are - strictly speaking - part of the specific pollen ornamentation (for example Chamaecyparis or Juniperus, see "Illustrated Glossary").

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