It’s Spring! Time to Stop and Smell the Roses!
Image Source: StefanoKass, via pixabay
Flowers have long been used by humans for gifts, decoration, and gardening. So, it wouldn’t be unreasonable to think that these floral displays are designed for human enjoyment, would it? The truth is, flowers have evolved over millions of years, long before the existence of human beings, and for one purpose only … reproduction.
When admiring the beauty of a flower, you are actually observing the reproductive organs of a plant. Kind of seems a little creepy, doesn’t it? But, in order to maintain genetic diversity within species, outcrossing must be promoted over inbreeding in plant populations. So rather than relying on wind or water to disperse pollen, plants have evolved to favor the more efficient use of animals as vectors.
It is for this reason that plants have developed such a diverse range of colours, sizes, shapes and fascinating quirks, so they can attract their animal pollen vector.
Bird Pollination – Ornithophily
Image Source: GeorgeB2, via pixabay
Bird pollinated flowers are commonly red, pink or orange in colour and generally lack a strong aroma. The tubular or bell shaped flowers do however, contain abundant nectar as a food reward for the birds and occur in clumps or inflorescences, rather than as singular flowers. The pollen is usually placed on the forehead, face, or beak of the bird so that it can be transferred as the bird moves from flower to flower.
Insect Pollination – Entomophily
Image Source: Dalibor Stanisavljevic, via flickr
Insect pollination is by far the most common form of plant pollination. These flowers occur in a wider range of colours than bird pollinated flowers, yet are often not as brightly coloured. Insects use the ultraviolet light (UV) part of the spectrum to see, so they can visualize patterns on flowers that humans can’t, it is these patterns that lead the insect to the pollen site.
How insects visualize flowers. Video source: Robin Noorda, via YouTube
These flowers are also smaller, to accommodate the smaller body size of insects and do not need to produce abundant nectar as an insect will consume far less pollen or nectar than a bird.
The co-evolution of plants and their insect pollinators, began much earlier than the relationship of plants and bird pollination, therefore becoming much more selective and species specific.
White flowers that open at night are specifically adapted for moth pollination and plants that mimic the appearance and aroma of carrion (rotting flesh) are specifically adapted to attract flies as pollinators, such as the relationship between flies and the titan arum (Amorphophallus titanum) or the corpse flower (Rafflesia arnoldii).
Corpse Flower (Rafflesia arnoldii). Image source: vil.sandi, via flickr
Titan Arum (Amorphophallus titanum). Image source: James Gaither, via flickr
Another amazing species specific pollination relationship, is buzz pollination. The flowers require a specific vibration frequency that is only provided by bees, in order to get the pollen out of the anthers (pollen containing structures).
If you don’t want to watch the entire video, just skip to 1:40 – 2:15 for a demonstration of buzz pollination. Video source: Deep Look, via YouTube
But my favourite by far is orchid pollination. The specificity to which this occurs is phenomenal. From complex shapes, such as Duck Orchids (Caleana major) to the incredible mimicry of the Hammer Orchid (Drakaea sp.), they have not only evolved to look like certain insects, but can also mimic the pheromones emitted by the female insect during mating season.
Duck Orchids (Caleana major). Image source: Bree Iredale, author
Wasp pollination of the Hammer Orchid. Video source: darkbrook, via YouTube