Sunday, March 18, 2012

Spring quite literally springing....


It's easy to overlook liverworts. These simple plants were the first to colonise the land and have been around for over 500 million years so in terms of durability, having survived five major mass extinction that wiped out many other life forms, they are unequalled in the plant kingdom. For most of the year they are pretty dull - just a mass of ground-hugging lobed green thalli confined to permanently damp places like the banks of ditches.  But for a few weeks in spring they do something rather extraordinary.


In late winter the surface of a liverwort thallus is a hot-bed of sexual activity. Embedded in the thallus are microscopic pits that release thousands of tiny male cells that swim across wet surfaces using their whirling flagellae. They're heading towards microscopic female structures called archegonia that contain an egg cell and are located under the edge of the thallus. Once fertilisation is achieved a spore capsule forms, like a small dark bead on the surface of the thallus, and when it's ripe the spore capsule stalk begins to elongate - very rapidly.


The images here are of the thalloid liverwort Pellia epiphylla and in the top image you can see a couple of spore capsules with their stalks just beginning to elongate.




































After a few hours the stalk (seta) is clearly visible and from this point it elongates very rapidly ..



... so after about a day the whole structure is a couple of inches tall and resembles a match with a glassy stalk.




































Then the capsule wall splits open into four segments and the contents literally explode, when elongated, compressed cells called elaters act like springs and hurl the spores into the airstream. You can see the process in more detail and in action by clicking here..... or if you collect some Pellia from the banks of a ditch (woodlands are a good place to look for it) you can watch the whole sequence for yourself.


Simple, primitive but very effective, it has served liverworts well for half a billion years.


There's a nice time lapse sequence of elongating spore capsules of another genus  here.

6 comments:

  1. Wonderful, isn't nature amazing? I like the video.

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  2. I often look out for liverworts but only seem to find the standard four or five really common ones. This one is super.

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  3. The capsules 'explode' quite rapidly when they're ripe, lotusleaf..

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  4. The elaters writhe like snakes as you watch them, toffeeapple...

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  5. I only rarely find leafy liverworts with spore capsules John - the capsules have a very short life, compared with those of mosses..

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