Thursday, 14 June 2012

The Portuguese Oak

I have decided to honor Portugal with this week’s post for two reasons: to celebrate the National Day of Portugal (which was last Sunday , the 10th of June), but also to support the Portuguese team at the UEFA Euro 2012. So I have decided to bring you today the Portuguese national plant – Quercus suber, the cork oak.

Quercus is a monoecious anemophilous plant, meaning that the sexual organs are separated in different flowers and are wind-pollinated. Thus the flowers are simple, small and shy, with a rather simple structure, but I thought this is a good opportunity to introduce you the wonders of wind-pollination. Anemophilous plants (wind-pollinated) are mainly found in two orders: Fagales and Poales and this, first of all, give us some clues about the environment shared among wind-pollinated plants. They are either trees (Fagales) or grasses (Poales), possibly due to the fact that flowers bloom high in the canopy, where the pollen is easily reached by the wind, but not as much by small insects. Another reason is possibly the windy and dry conditions found in steppes or desert-like environments where grasses reign. In such environments, the wind is a common and available resource much prevalent and reliable than insects. Possibly, also due to the winds typical of such environments insects are here less abundant comparing with, for example, forest-like environments. For this reason, plants found here have started to invest their energy in other characters, allowing a more efficient pollination and thus the flowers became adapted to wind pollination.

To make it easier for you to understand the main differences between anemophilous and entomophilous (insect-pollinated) plants, I have made this table to share with you:

Comparision between Anemophilous and Entomophilous floral characters

Because anemophilous plants have no need to attract anything, there is no need to invest energy producing big showy flowers, or expensive precious nectar. Instead, these plants produce many small flowers and large quantities of light pollen, which can be easily carried away by the wind. To facilitate the wind to take the pollen away, the petals are much reduced, and sometimes they are completely missing. Likewise, the stamens are hanging outside the flowers, waiting for the breeze.

Male inflorescence of  Quercus suber with the stamens hanging outside the flowers

Also the typical inflorescences found in Fagales are definitely adapted to this pollination syndrome. Catkins of small and light flowers are easily moved and shacked even by a light breeze, and this allows the pollen to be released and spread easily. Because the pollination isn’t specialized like in entomophilous plants, the stigmas also have to be adapted to the wind pollination, so the surface of pollen reception is much bigger. This can be very easily observed in Poales, where the stigmas are long and feather-like, increasing the surface for an effective pollen reception.

Feather-like stigmas typical of grasses. Left: Arrhenatherum album; Right: Ammophila arenaria (Source:

Also, the position of the inflorescences in the tree isn’t random – male flowers are found in the lower older twigs and female flowers in the upper younger twigs. This is to avoid self-pollination (it is more unlikely that the pollen from below flies up and fertilizes the female flowers, but if female flowers were below, any pollen grain falling from the catkins above could fertilize them).

Flowers and inflorescences of Quercus suber

Wind-pollinated flowers are so shy that they can be unnoticed many times, especially by non-botanists. The truth is that they are not hiding, they are right there and it is fascinating to observe all the structures that seem to be undercover by the green foliage. Finding them is like finding a precious treasure, which is visible for everyone, but unnoticed by most people. That is the reason why every time I show wind-pollinated flowers to non-botanists they become astonished and quite surprised... These flowers might not be the prettiest, but they are pretty cool too.