A violet-ant mutually beneficial symbiosis

 

Sweet violets Viola odorata produce two types of flower - the familiar scented kind that are amongst the first wild flowers to appear in spring and are pollinated by bumblebees, and a summer cleistogamous version that remains as a closed bud and self-pollinates without the intervention of insects. Insect pollination in early spring can be a chancy, hit-or-miss affair but, come what may, the cleistogamous flowers aways produce seeds in early autumn. This is a seed capsule of one such that I found in the garden, splitting open in three segments to release its seeds. Each seed has a small, white, oily attachment, an elaiosome, that ants find irresistible. They carry the seeds away so, if you grow violets in a garden, seedlings are likely to appear in unexpected places.

I’ve sown some freshly collected sweet violet seeds now, because they’ll need vernalisation, subjection to the freezing temperatures of winter, to break their dormancy.

 

Choke fungus - Epichloe typhina

These strange white sheaths around the stems of grasses are the spore-producing tissue of the fungus known as choke Epichloe typhina. It's present inside the grass all year-round, living as microscopic hyphae within the spaces between cell and benefitting from sugars produced by the host's photosynthesis, but is only visible to the naked eye in summer, when it produces its spores externally around the stem. The white fungal sheath will turn orange-brown when the spores are ripe and ready to be shed, when they are often carried away by small flies.

 The fungal infection tends to prevent the grass culms from flowering, promoting multiple shoot formation instead, but in return the fungus increases its host's drought resistance and produces toxic alkaloids that deter grazing animals, so the relationship between fungus and grass is symbiotic and not simply parasitic.

I found these specimens growing beside a footpath at Wolsingham, Weardale this week.

A Lichen with Teeth

We found some very fine specimens of dog lichen Peltigera sp. when we were out  walking at Shittlehope Burn at Stanhope in Weardale this morning. I've often wondered why it's called dog lichen - I've found one or two references that suggest that Linnaeus gave it the Latin specific epithet caninus because he saw some resemblance to a dog in its shape, which I find hard to see, unless it relates to the menacing tooth-like structures, called rhizines, on the underside of the thallus.

The arrangement of the rhizines, which are extensions of the fungal part of the symbiotic partnership between alga and fungus that constitutes a lichen, are key identification features and as soon as I can get my hands on a lichen field guide I'll try to identify the species more accurately.

Some Peltigera species contain cyanobacteria that fix nitrogen in the symbiotic partnership, so the organism then has its own in-built nitrogen fertiliser supply and plays a part in the cycling of nitrogen in ecosystems.