Flower Answers

by Deb on February 24, 2012

Flowers

1. It’s very difficult to tell when flowering plants developed, but it was probably before and during the Cretaceous, the last age of the dinosaurs. Like animals, plants were still ‘experimenting’ with the challenges of being on land, where there is no cushioning water to bring you nutrients and carry away your spores. Land is a lot harder environment to survive in, especially if you can’t move, and creating and protecting the next generation until it can look after itself makes it even more complicated.

The different parts of flowers developed over time, first pollen and ova and ways to distribute them, a place for fertilisation and the development of the embryo and seed, structures to protect them, and finally something to attract animals to help move the pollen around. It’s possible that early flowering plants were around as many as 250 million years ago from chemicals that have been found, but there is better fossil evidence for them at 125-130 million years ago. Throwing in molecular evidence from changes in DNA and it gets more confusing, suggesting that the major groups of flowering plants split from each other around 140 million years ago. This is why we use many different lines of evidence and try to see how they fit together!

2. Calla Lillies and sunflowers are the flowers that aren’t – technically they are inflorescences, which is groups of flowers growing from the same stem. Many of them look like separate flowers, but some are so modified they look like a single flower.

The large central disc of a sunflower is actually hundreds of tiny flowers with a common stem, each produces a seed. The outer ones are modified to grow larger petals, which makes the whole thing look like a single flower.

sunflower

Calla lillies are a different type of inflorescence. The ‘spike’ of the lilly is made up of lots of tiny florets, while the large white ‘petal’ is actually a highly modified bract.

3. A flower’s main job is to provide a place for fertilisation and the embryo to form, however the majority we know are also there to attract animals. Because flowering plants use sexual reproduction, they have to find a way for the pollen and ova to get together.

Ova stay in the protected area where the embryo will develop and pollen moves, either from flower to flower on the same plant or between different plants. There are two main methods for moving pollen – using the wind or using animals. Flowers of wind pollinators tend to be small and bland, like most grasses. (This is, incidentally, the cause of hayfever – all that grass pollen floating around in the wind trying to hit another flower.) It works well for grass because there’s so much of it – pollen blown off one grass stalk has a pretty good chance of hitting another grass stalk.

However most plants are not ubiquitous and need a bit of help to get their pollen from one flower to another, which is where animals come in. And that is the reason for all the fancy petals, scents and nectar we see – to suck in their accomplices. The animals, generally insects or birds, get some sugar or are tricked into visiting the flower where they are coated in sticky pollen. Then they head off to the next flower and the pollen hitches along with them to get to the new ova. When you think about it, our love of beautiful flowers just means they are doing their job very well and we’re cheating by not transferring pollen for them. Even worse for some plants, we’ve modified them so much they can’t live without us any more.

4.     Bracts are specially modified leaves just below the flower or inflorescence. Sometimes they are green and function as leaves, but they can also play a role in both jobs of the flower. The most commonly known bracts can act like petals to attract pollinators, especially ones with bright colours like poinsettia or bougainvillea.

bougainvillea

They also have a role in helping to protect the important reproductive parts. This can be by distracting herbivores who eat the large, obvious bracts rather than the important ovaries and pollen, or helping to protect them from rain and wind.

5.     The photo is a Titan Arum or Amorphophallus titanum, the largest unbranched inflorescence in the world that can reach 3m tall. It is related to the calla lilly and has the same form of fake flower – the spike carries lots of little flowers and the enormous ‘petal’ is actually a bract. It is one of a group of plants called carrion flowers or corpse plants because they smell like rotting meat. This isn’t anything sinister, just that they are trying to attract flies and carrion eating beatles to pollinate them. It is also deep red and the spike of flowers generates heat to make it more like meat.

They do not flower every year in the wild and even less in botanical gardens, but people are getting better at collecting pollen and there are more of them around, so there are usually a few that flower around the world every year.

 

And this is a great excuse for some beautiful time lapse photography.

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