Apples on sticks

Yesterday the south-east group of the British Bryological Society visited the town of Wadhurst in the far east of Sussex, near Tunbridge Wells. A variety of habitats including streams, woodland, grassland and ditches led to an array of moss and liverwort species being recorded. All were new for the area as this was a place no bryologist had dared to tread before.

Highlights included my favourite liverwort, the large and fragrant Conocephalum conicum (Great Scented Liverwort), as well as non-bryophytes such as two new plant species for me – Orpine and Soft Shield Fern – and a new carabid in the form of Carabus monilis with its bronze lustre. However, apparently the best find of the day was one of mine. This was the apple-moss, Bartramia pomiformis.

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Bartramia pomiformis

This moss immediately struck me, growing on a sandy bank on the edge of a narrow lane. The patch was almost perfectly circular, a richer green than the surrounding winter vegetation. And it was easy to see how it got its name, from the rounded apple-like capsules.

These capsules, that many mosses have in some form or another, form the final stage in the life cycle of a moss. The capsules contain the spores. Like a fruit, the capsules darken with maturity, starting off green such as these but soon becoming dry and brown with age, at which point the spores will be released.

These spores, upon germination, will then grow into a protonema, which will develop into a sheet of felt-like rhizoids, from which the gametophore will arise. The gametophore will be the stage of a moss that many people will be familiar with. It is the typical plant-like form, with stems and leaves, resembling a flowering plant although without vascular structure. This means that mosses lack the transport systems that vascular plants use to transport water, nutrients and minerals to their cells through tubes such as the xylem and the phloem.

Mosses can be dioicous or monoicous. Dioicous mosses have the male and female reproductive organs on different individual gametophores, while monoicous mosses have both sex organs on the same plant. In both cases, the sperm from the male sex organ will be transported to the female sex organ by a drop of water, which is one reason why there is a higher density of moss species in wetter climates such as the Atlantic rainforests of western Scotland and Ireland.

Once fertilisation takes place, a sporophyte begins to emerge from the venter, where the embryo develops. Over a period of many months, a seta (stalk) will grow, on top of which a capsule will be produced. Eventually this will release spores, and the cycle will repeat itself.

When diving into the life cycles of many taxonomic groups, I am often amazed by the complexity behind what appear to be fairly simple organisms at a cursory glance.

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