When I was writing about the wildflowers and plants of Hvar, I intended to include a couple of photos of mosses. I was greatly taken with the feathery green clumps I’d seen on shady walls and paths through the local woodland. However, having worked hard to identify the flowering plants, I was completely intimidated by putting a name to any of the mosses. So I wimped out, telling myself that the article must be published while the flowers were still in season!
One year on, I pretty much still have that gap, and mosses are local plants, even if they don’t have flowers or seeds. And I’m also keen to find out about lichens too, which grow just about everywhere here. Lichens, of course, are not plants, which was news to me as I started reading about them. So, we’ll now be including fungi of Hvar as well!
Mosses are tiny plants, typically growing in clumps only a few centimetres high, taking in water and nutrients via their leaves (not roots) and creating food by photosynthesis. While the world’s largest moss can grow up to 50 cm in height, none of the ones I’ve yet to see on Hvar are anywhere near that! To see any kind of detail on our mosses I have to get up really close and personal, and the macro setting on the camera is crucial!
Individual moss leaves are simple, usually only one cell thick, attached to a stem. These are not flowering plants, they reproduce by spores as do ferns, who also prefer shady and damp places. So far so good, but now let’s get into the sex life of mosses so we know (vaguely) what we’re looking at.
Moss spores germinate to form a structure of filaments that typically looks like a thin green felt, which may grow on damp soil, tree bark, rocks, concrete, or almost any other reasonably stable surface. When it grows up into the adult stems and leaves, this is what we generally think of as moss. This green clump produces all the food for the plant, taking in everything it needs via the leaves. The threadlike “roots” on the underside are only there to hold on, not to draw water or nutrients from whatever they’re growing on.
From the tips of the stems grow the parts of the moss that participate in fertilisation, producing cells with two sets of chromosomes. The female gamete looks like small flask-shaped clumps of cells protected by a modified set of leaves. The male gamete is also surrounded by protective leaves, which in some mosses form a cup shape, allowing the sperm to be splashed out by falling drops of water, where it hopefully makes contact with a female gamete. Male and female parts may occur on the same plant, or separately on different plants. Following fertilisation, the sporophyte grows out of the flask, taking around 3-6 months to mature. At that point it will have a long stalk with a single capsule at the head, containing spores ready to start the cycle again. Most mosses rely on the wind to disperse the spores.
Being able to identify individual mosses takes experience, a magnifying lens and good timing. Browsing the field guide on the British Bryological Society I can see just how much variety I’ve overlooked in these tiny green plants. I may learn to spot an acrocarp (upright growth with capsules at the top of stems) from a pleurocarp (wefts or mats spreading horizontally with capsules growing from the side of stems) but for naming individual mosses I have to get my timing right. The appearance of the gametophytes and sporophytes are as crucial to identifying mosses, as flowers are to, well, flowering plants! Plus, I need to find a good source of information about local varieties. I’ve had a stab at identifying the mosses in the photos above, but would be very happy to hear from anyone with more knowledge!
There are approximately 12,000 species of moss, all now classified under Brytophyta. In Croatia, 638 taxa have been identified, of which 7 are endemic. However, there’s not yet a complete inventory, due to a lack of specialized researchers, and it’s estimated that the total number of mosses in Croatia is around 700.
Lichens are structured rather differently from plants, being a combination of fungi and algae in a relationship that brings benefits to both. The most apt description I’ve read is that the fungus is a farmer, cultivating its alga for food while protecting it from harm. Unlike a fungus, the alga contains chlorophyll, and can generate carbohydrates from sunlight, water and air – photosynthesis.
Lichens are named primarily for the fungus partner, which can look a lot different from their independent form, or even lichenized with different algae. The alga in the partnership may be a green alga or what used to be called a blue-green alga but now known as a cyanobacterium. Just occasionally, both types are involved. And recent research has identified yeasts that are sometimes present, possibly producing chemicals that help protect the lichen from microbes and predators.
The main body of the lichen comes in a wide variety of forms, from branching tufts, leaf-like structures, filaments, platelets, crusts, powdery granules – and sometimes little or nothing to see on the surface. Identifying the lichen can be a tricky business – even for the experts. I’m going to confine myself to naming the fungus where I can, and leave it at the form type for the rest. The common names of lichen only muddy the waters, as many of them are traditionally called “mosses” – e.g. wolf moss, reindeer moss, etc. Which, they clearly are NOT!
Foliose – grows in flat, leaf-like lobes, which may be attached to the substrate or partly lifted away. These are the largest and most complex of the lichens, with the probiontic layer covered by an upper and lower surface of fungus filaments. The lower surface is often differently coloured, frequently brown or black.
Fruticose – have upright or hanging branched structures, with either round or flat cross-section. The branches are covered by a single fungal layer. Attached to the substrate from a single point by a disc-like holdfast or clusters of rhizoids.
Crustose – is crust-like, firmly attached all over. Has an upper surface of protective fungus only, the probiontic layer is in contact with the substrate and may grow into it. Which means this type can’t be collected intact without taking part of the underlying substrate with it! Surface may be smooth or lumpy, possibly divided into sections. Identification requires at least a hand-lens, and possibly a microscope or chemicals to fully determine. Placodioid – a variation of crustose lichen, with distinct radiating lobes on the external edge. Still lacks a lower cortex but may not be firmly attached.
Squamulose – grows in small flat scales, often overlapping, lifted off at the tips. Like crustose, there’s only a single surface, although the underside may be a different colour. The best example of a squamulose lichen is Cladonia. Its primary thallus is squamulose and secondary thallus is upright and cylindrical with a hollow stalk having apothecium at its tip.
Leprose – surface is powdery granules containing algal cells and fungal hyphae with no overlying cortex.
The number of documented lichens in Croatia stands at 930 (out of an estimated 17,000 fungi) of which 82 are endemic to the region. Of the rarer lichens, 20 have a strictly protected status, while 5 of the common lichens are allowed for supervised commercial exploitation. E.g. Lobaria pulmonaria is collected for pharmaceutical use.
Lichens can grow on all sorts of surfaces, both natural and man-made, rough or smooth. Many lichens are quite grey when dry. However, once they’re wet, the surface becomes transparent, and the underlying algal cells give it a deeper colour. For others, the fungus contains a colourful pigment. Making dyes from lichen is traditional in many places. The process varies, but roughly speaking goes like this: add the lichen to water or dilute ammonia (aka urine in many societies), which you then leave for several weeks. The resulting dye can turn out a very different colour from the growing lichen – brown, gold, orange, green, purple, blue and red – depending on the lichen type, and variations in the extraction process. Litmus, that standard method for determining the pH of a substance is a mixture of dyes extracted from lichens, including Rosella tinctoria.
You can use lichens in other sciences too. As they are among the first organisms to grow on a newly exposed surface, their size can be used to determine how long the surface has been exposed, based on the assumed rate of growth. This has a host of uses in fields such as archaeology, paleontology, and geomorphology. Lichen can be preserved on old rock faces for up to 10,000 years, though lichenometry is most accurate for surfaces less than 1,000 years old, and particularly useful below 500 years, where radiocarbon dating techniques are less accurate.The lichens most commonly used for lichenometry are Rhizocarpon and Xanthoria.
I feel I’ve only just scratched the surface of mosses and lichens, so I’ll be keeping an eye to the ground throughout the year to see if I can learn more about these fascinating plants/fungi!
British Bryological Society promotes the study of mosses and liverworts