Hydroponic Plant suggestion

I work in a lab and we found an old (small) volumetric flask that someone had previously planted something in. The flask was full of soil, rocks and fungus gnats and took us ages to clean out due to the long narrow neck of the flask.

We want to add a new plant but don’t want to put more soil in the flask since it was a nightmare to clean so thinking something grown in water.

I have grown cuttings etc in water but always transplanted after they had produced roots. Is there anything that is more suited to being grown hydroponically? Maybe some sort of trailing plant to suit the neck of the flask?

It will be living in a pretty sunny spot but in the UK. Any suggestions and also care tips welcome! Tia!