Pollen Features can be Ambiguous

Case studies:

— interpretation of specific aperture conditions

— classification of infratectal structure characters

— deviating pollen forms Investigation of a morphological series within a genus can provide decisive nomenclature or at least support such a decision; studying only an isolated sample of a morphological series may easily lead to misinterpretations. Passiflora (Passifloraceae) pollen is an example of a morphological series concerning apertures. The apertures in Passiflora cf. incarnata may be interpreted as three ring-like apertures. An interpretation as porate-operculate is likewise possible, and probably more correct, if compared with pollen of other Passiflora species.

Not infrequently the apertures in angiosperms show indistinct margins, or appear as thin regions in the pollen wall. The Illustrated Glossary makes use of two terms, poroid and tenuitas, in describing superficially quite similar features.

A poroid is a circular or elliptic aperture with indistinct margin. A tenuitas is a general term for a pollen wall thinning, which has been applied to many different features (KREMP 1968, HARLEY 2004, PUNT et al. 2007).

A tenuitas (in angiosperms) is normally found additional to regular apertures (e.g., in some Myosotis species, see "Illustrated Glossary").

The harmomegathic effect may cause misinterpretations. A distinct infolding type suggests or pretends an erroneous aperture condition, while the correct aperture condition is inconspicuous or even hidden.

Pollen of Sparganium erect um (Sparganiaceae) is in dry stage infolded, boat-shaped, and would be considered as sulcate. In fact Sparganium pollen is ulcerate, the ulcus is seen clearly in the hydrated, spherical pollen stage.

Nymphaea alba (Nymphaeaceae) pollen has asymmetrical halves. The features

Ambiguous features

Passiflora cf. incarnata Passifloraceae left:

polar view right:

equatorial view left:

Passiflora citrina Passifloraceae stephanocolpate operculate polar view right:

Passiflora suberosa Passifloraceae stephanocolpate operculate, dry pollen

Ambiguous features

Passiflora cf. incarnata Passifloraceae left:

polar view right:

equatorial view left:

Passiflora citrina Passifloraceae stephanocolpate operculate polar view right:

Passiflora suberosa Passifloraceae stephanocolpate operculate, dry pollen

of the smaller distal half can be interpreted either as a large ulcus with a conspicuous operculum, or as a more-or-less equatorially situated ring-like aperture surrounding the polar area. Ultrastructural characters and germination experiments support the interpretation as a ring-like aperture (HESSE and ZETTER 2005).

Ambiguous features

Myosotis palustris Boraginaceae left:

equatorial view heteroaperturate, alternating colpori and colpi (pseudocolpi)

right:

polar view polar area with triangular tenuitas

Ambiguous features

Sparganium erectum

Sparganiaceae ulcerate left:

equatorial view right:

dry pollen boat-shaped

Ambiguous features

Nymphaea sp. Nymphaeaceae ring-like aperture left:

equatorial view right:

dry pollen cup-shaped

Ambiguous features

Myosotis palustris Boraginaceae left:

equatorial view heteroaperturate, alternating colpori and colpi (pseudocolpi)

right:

polar view polar area with triangular tenuitas

Ambiguous features

Sparganium erectum

Sparganiaceae ulcerate left:

equatorial view right:

dry pollen boat-shaped

Ambiguous features

Nymphaea sp. Nymphaeaceae ring-like aperture left:

equatorial view right:

dry pollen cup-shaped

Infratectum is a term which includes in fact a morphological series. The classical angiosperm character states simply comprise columellar and granular. However, as, e.g., DOYLE (2005) has pointed out, intermediate conditions are not uncommon. Even the areolate infratectum, usually restricted by definition to gymnosperms, is found in some angiosperms (see "Illustrated Glossary").

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