Life Without Sex?

We Do It Both Ways!

All lichens and bryophytes can reproduce themselves asexually and a great many (but not all) are also known to reproduce sexually. Sexual reproduction involves the mixing of genes from two different individuals whereas in asexual reproduction there is no mixing of genes and an individual reproduces copies of itself, like a clone.

Reproduction Without Sex

If a fragment of a lichen or bryophyte breaks off and lands in a suitable habitat it may grow into a new individual. In principle this is the same process as propagating plants by taking cuttings, a technique familiar to many gardeners. Instead of simply relying on accidental breakage, many lichens and bryophytes help matters along by creating various forms of vegetative propagules.

Stems of the moss Campylopus clavatus have a line of weakness near the apex. The top bit of the stem, with the attached leaves, breaks off easily and can grow into a new plant (above right).

In this close up you can see several broken branch tips.

Bryophytes

Many bryophytes produce tiny spherical or disc-like granules, called gemmae. Each gemma consists of a small cluster of cells and if one of these gemmae lands in a suitable habitat it can grow into a new plant. Some thallose liverworts, such as Lunularia and Marchantia, produce their gemmae in small circular or semicircular gemma cups which sit on the lobe surfaces. However many mosses and leafy liverworts produce gemmae directly on the leaves or stems, rather than in any specialised structures.

A species of Marchantia showing the circular gemma cups.

A moss in the genus Tortula showing numerous granular gemmae on the leaf surfaces.

Lichens

In many lichens the upper surface has powdery areas. Each granule of this powder consists of a few photobiont cells wrapped up in some fungal cells. Wind, water or animals may carry these granules, or soredia, away to form new lichens elsewhere. Some lichens produce very tiny and fragile finger-like outgrowths called isidia, typically less than a millimetre long. The isidia contain both the fungal and photobiont partners and are easily broken off and dispersed. Like soredia, the isidia can grow into new lichens.

The isidia on the foliose lichen Xanthoparmelia australasica.

Soredia on the foliose lichen Xanthoparmelia xanthofarinosa.

What, Never?

Life without sex is obviously sufficient for various lichens and bryophytes. In some lichens, such as Chondropsis semiviridis and Thamnolia vermicularis, sexual reproduction has never been seen and in many bryophytes sexual reproduction appears to be quite rare.

Sexual reproduction has never been recorded in Thamnolia vermicularis, a fruticose lichen.

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