Myrtaceae



Eucalyptus globulus
Native Plants of Montara

Ilex mitis
Eucalyptus globoidea
Newcastle Pollen Database



Eucalyptus camaldulensis
Letitia Silberbauer UNE

Myrtaceae:
Typically recorded as "Eucalyptus," several genera have this general morphology. Myrtaceae pollen is typically oblate and triangular in polar view. The apertures are short furrows in a thickened portion of the wall. The distinctive pattern typically seen in polar view is formed by thinning of the exine, resembling a syncolpium. This thin region often has a triangular island of thick tectum at the pole of the grain. Sculpturing varies from psilate to reticulate.

Pollen of the Myrtaceae is an important historic indicator in arid regions of the northern hemisphere. Eucalyptus is the most commonly-planted genus, but many other genera are used horticulturally. The morphology similar to that described above also occurs in Acmena, Angophora (retic.), Backhousia (no tectum island), Baeckea, Callistemon (rough wall distinct island), Calytrix (broad aperatures), Choricarpia, Leptospermum (faint tri-radiate mark), Lophostemon, Melaleuca, Rhodamnia, Rhodomyrtus, Syzygium, Tristaniopsis, Ugni

Plants:
About 3000 woody trees or shrubs with thick leaves containing oil glands. Flowers with 5 sepals and petals and many stamens. Fruit generally a woody capsel. Gondwanan. Tropical and subtropical, mostly in Australasia but with 45 genera in central and south America, 2 in Africa, and about 20 genera native to India and Asia. Cultivated throught the world for shade and as ornamental plants. Cloves (Syzygium aromaticum) and allspice (Pimenta dioica) are important economical species of the Myrtaceae. The pollen is harvested by honey bees.

Pollen light micrograph:
In maceration mounts, the small (20 - 30 µm) grains are almost always oriented so the polar area is visible. Below are three categories present in samples from a single bee hive from California. Note the range of shapes and sculpturing.

Pollen scanning electron micrograph (SEM)
The remarkable contrast of thick tectum adjacent to the thin tri-radiate mark is striking in the SEM above. Note the intine or cell membrane protruding through the apertures.

Production and Dispersal:
High pollen production but moderate to poor dispersal.

Preservation:
Moderate to poor due to breakage.

Fossil Occurrence:
Based on its Gondwanan distribution, the family has existed since the Cretaceous; the introduction of Eucalyptus into the Mediterranean region and southern California began in the Nineteenth century. In Spain and Calfornia, it is a usefull marker for the historic period.

References:
Links
Owen Davis 10/02