Time-tested rites of ancient plants

Wolsingham, Weardale The sexual success of thalloid liverworts has ensured their survival for millions of years

Peering down at the emerald lobes of Pellia epiphylla liverwort covering the sides of the ditch, I could see this had recently been the site of intense sexual activity.

On mild, wet days, tiny pockets embedded in the plant's surface release swarms of swimming male sex cells, each only a few thousandths of a millimetre long. Powered by two lashing flagellae, they gyrate in the surface film of water and swim towards chemical attractants released by egg cells, hidden under a flap of tissue near the tip of the flat green thallus. Most fall by the wayside, exhausted, but a few, perhaps aided by rain splash, reach their destination. The evidence of success - small, round spore capsules resulting from fertilisation - was plain to see.