This is a gametophyte of the fern Asplenium scolopendrium. It is only about 2mm across and is composed of a heart shaped sheet of cells that is only one cell thick. Fern gametophytes are easy to grow and you can do it at home.
Finding spores
First you need to find some fern spores. You can buy some online by searching with the phrase "buy fern spores online" or you can find some on a fern plant in late summer.
To find some on a fern, choose a fern leaf in late summer, when it has brown dots on the underside of the leaf as in the photograph below.
The brown dots are called sori (singular - sorus) and each one is a collection of sporangia (singular - sporangium). This photo shows a leaf whose sporangia have already dehisced. This means that they have already opened and allowed the spores to fall out. If you find a leaf whose sporangia have not yet dehisced then the sori will be smaller and darker brown.
Find a leaf like this, whose sporangia have not yet dehisced, and lay it on a piece of paper in your house in a warm place, with the sori facing down. Leave it overnight.
In the morning when you lift the leaf you will find that there is a brown shadow on the paper, in the same shape as the fern leaf. The brown shadow is the pattern of fern spores that have fallen out of the sporangia on to the paper. Fold the paper and tap it so that the fern spores come to the middle of the paper. Fold the paper up and store it in the fridge. They will keep for about a year in most species.
Sowing the spores
You need a clean pot filled with potting compost. First scald the compost by pouring boiling water through it. This kills off any fungi that could harm the gametophytes.
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| Scalding soil before sowing fern spores. |
Next allow the soil to drain and cool completely to room temperature. Once the soil is cool, sprinkle the fern spores on the surface of the soil. Then enclose the whole pot in a large freezer bag. Inflate the bag by blowing into it, and knot it at the top. The picture below shows a blue bag, but the bag must be transparent, and should ideally be colourless.
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| Enclosing the pot in a bag to give a humid atmosphere and to avoid needing to water the pot. |
Put the whole assembly somewhere at room temperature by a window that is not too hot or bright.
In Cambridge I find that they grow unshaded in winter and are visible in about 2 months. In summer I have to shade them under a piece of paper when the sun shines directly in the window and then they are visible in about 4 weeks.
Check occasionally for growth. The pot will not need watered, until you remove the bag.
If you start to see fungus growing and making the gametophyte turn grey, remove the healthy gametophyes in clumps to a new pot and grow them without the bag. Make sure to keep watering them regularly so that the soil surface never dries out.
After a few more weeks you will see the tiny first leaf of the sporophyte plant developing.