If both a Greek and a corresponding Latin form exist for a prefix, then the Greek form is used consistently: panto- (not peri-), ekto-(not ecto-), or the Greek di- (dis-), and not the Latin bi- (bis-). There are few exceptions from this rule. If the Latin form is more widely used, then the term is treated as a nomen conservandum; for example, bisaccate is found exclusively in the literature and not the Greek form disaccate.
Some prefixes need a comment. Micro-is used to denote features <1 jm: micro-reticulate, -echinate, -verrucate, -baculate, -clavate, -gemmate, -rugulate. However, some possible combinations are not applicable; for example, micro-striate or micro-perforate. Striae are not known to be <1 |jm in length, and perforate by definition describes a feature <1 jm.
Terms not listed in the glossary belong to fern or moss spores, or are considered as obsolete, diffuse or redundant (e.g., multiplanar tetrad), superfluous (e.g., polyplicate, because plicate pollen grains are always equipped with several to many plicae), or may be a permanent source of confusion (zon-, zona-, zoni-, zono-).
1 "Pollen Terminology. An illustrated Handbook1 aims to clearly separate the types and classes of pollen. Pollen type is a general term categorizing pollen grains by distinct combinations of characters and is often used in connection with a distinct taxon (e.g., Polygonum aviculare type).
Pollen class2 is an artificial grouping of pollen grains that share a single, distinctive character. Pollen classes refer to pollen units, to aperture form and location, or to an extremely distinctive ornamentation character. Classes include the terms polyads, tetrads, dyads, saccate, inap-erturate, sulcate, ulcerate, colpate, col-
2 "Pollen type" is sometimes (colloquially) misused; for example, Croton type, which is a distinct feature of ornamentation and is correctly termed Croton pattern.
porate, porate, synaperturate, spiraper-turate, lophate, clypeate and plicate. These classes are useful in identification keys as they have a good diagnostic, although mostly no systematic, value. In general, a pollen grain may belong to more than one pollen class; in such cases the more significant feature should be ranked first (e.g., Pistia: plicate - inaperturate, Hemigraphis: plicate - colporate, Typha: tetrads - ulcerate, Rhododendron: tetrads - colporate).
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