There’s more to pollination than bees. Plants are sneaky. They’ll use anyone or anything to get what they want. From treats to treachery and imprisonment, here are some of their most uncommon pollination tricks.
A flower of Axinaea affinis, showing “bellows” style stamens. Image source: Dellinger et al., 2014, Current Biology.
Birds passing this Axinaea flower are in for a treat. Its stamens (pollen-producing organs) are attached to what looks like a delicious yellow berry. These eye-catching appendages are full of sugar, so the bird hops down to peck off a tasty treat.
Of course, the plant has a reason for producing these energetically expensive snacks. These appendages are made of spongy material, full of air. The black sticks are the anthers where the pollen is produced. In this flower they’re hollow with a pore at the far end.
When a bird’s beak clamps down on the spongy appendages, the air inside is squeezed out through the anther like a bellows, blasting the bird with a face-full of pollen, which is carried to the next plant when the bird moves on.
The giant Amazon water lily (Victoria amazonica) is an amazing plant. Its leaves can reach over 2.5 metres across and its beautiful flowers are over 30cm wide, but they live for just two days.
On its first evening the magnificent bloom opens, revealing white petals scented like pineapple. Beetles are attracted to the flower not just for its fragrance, but for the heat that the flower provides; around 10°C higher than the surrounding air. The flowers are female on the first night, and as the beetles enter they transfer any pollen they’re carrying onto the stigma.
In the morning the flower gets sneaky, trapping the basking beetles inside.
During the day the lily flower turns pink and becomes male, showering the scrabbling beetles inside with pollen. On the second evening, the flower opens once more, this time without scent or heat. The pollen-dusted beetles leave to search for another white flower, and the pollination continues.
Cologne for bees
A beautiful male Euglossa bee. Image from Wikipedia
The bucket orchids (Coryanthes sp.) produce aromatic oils for one purpose; it’s cologne for bees. Males euglossid bees collect the esters and other fragrant chemicals from the flower to impress the ladies, but in their excitement and jostling they often fall into the water-filled bucket of the flower. Their wet wings and the slippery sides make their escape almost impossible, except through an escape tunnel with bee-sized footholds. Handy.
You can see the escape spout in this Coryanthes alborosea flower on the left. Image from Wikipedia.
The escape tunnel of bucket orchids is very narrow. Bees take around 30 minutes to carefully climb out to safety, but not before being adorned with a pollinium, an aggregated mass of pollen grains. On their next dip into a bucket orchid, the pollinium rubs off onto the stigma inside the entrance to the escape tunnel.
The scent droplets produced by the plant dry up by the time the bees have escaped the flower, which encourages the bee to visit another flower the next time it wants to apply cologne.
There are around 750-850 species of figs (Ficus), each with its own species of pollinating fig wasp. Each is totally dependent on the other for successful reproduction. I’ll explain, but first, step away from any fig-based foods you might be eating.
A cross section of a fig. Image from Wikipedia.
A fig fruit is a synconium, a bulbous stem containing hundreds or thousands of flowers, completely enclosed but for a narrow ostiole (hole) that only allows a specific species of fig wasp to enter. Female fig wasps crawl into the ostiole when they are ready to lay their eggs. The passage is so narrow that the wasp usually loses its wings and antennae, so she is doomed to die within.
(Some of the figs we eat come from sterile species that don’t require wasps. Others, however, do have… deceased occupants).
The fig contains three types of flowers; male, short female and long female. The wasp lays its eggs in the short female flowers, but it can’t reach down into the base of the longer females. Instead, these flowers are pollinated with the pollen the adult female carried from her original host fig and develop into seeds.
A fig with its wasp inhabitants. Image from Wikipedia
When the larvae hatch they feed on their host short female flower until mature, receiving a coating of pollen from the male flowers as they move within the fig. The adult males are wingless and have two important jobs to do. First, they mate with the females. Next, they chew a hole out of the fig through which the females can escape. Then they die.
The females, coated with pollen, then emerge from the fig to find a new place to lay their eggs.
Zostera marina‘s tiny flowers release and capture pollen underwater. Image source: Wikipedia
We’ve seen plants trick-or-treating animals into carrying their pollen, but what happens when a plant spends its entire life underwater?
Zostera (eelgrass) is a seagrass, a true flowering plant. It employs a little known type of pollen dispersal called hydrophily. Its tiny male flowers release streams of pollen into the surrounding water, which have a few special adaptations for life under the sea.
It takes time to find another receptive flower without dedicated pollinator-transport, so eelgrass pollen has the same density as water, allowing it to drift in the current for days without floating or sinking.
Zostera pollen is elongated. While spherical pollen must be directly upstream of the female flower to pollinate it, longer thread-like pollen grains can be caught in the flow and eddies of water around the plant and eventually swirl into place on the female flower.
Over to you
Competition for pollinators has led to plants exploiting a huge range of animals, as well as wind and water. Do you know of any weird and wonderful kinds of pollination? Let me know in the comments below, or message me on Twitter @JoseSci!