Scientific Illustator Out and About: Introduction to Lichens - August 23rd 2013

Story posted: Friday, 23. August 2013 by Lizzie Harper

Botanical illustration involves illustrating what are traditionally known as the “lower plants” as well as the green leafy ones.  Lichens fall into this category (along with the very different mosses, and liverworts) although in fact they’re much closer relatives of fungi.

Lizzie Harper botanical illustration of lichen

Study of Xanthoria parietina and Parmelia sulcata

Having been on a lichen course with Ray Woods, through RWT and written it up “Fungal foray, lichens and dragonflies – October 15th 2012” I was keen to learn more.

I'm member of the brilliant Institute of Analytical Plant Illustration (IAPI) who organise workshops for their members, including one on lichens.  This organisation promotes understanding between botanists and illustrators and is a really friendly bunch of enthusiasts and experts.  If you’re into botany, or illustration, it’s well worth joining; I have learnt masses from their workshops and meetings and relish the chance to meet people with shared interests.

In July, I went on an excellent (and very reasonably priced at £10 for members) IAPI “Introduction to Lichen” course at RHS Hyde Hall.

This was taught by John Skinner, an eminent lichenologist with the British Lichen Society with a real ability to communicate his knowledge and enthusiasm in an accessible way. (He’s doing another lichen course at the FSC in September).

The images for this blog are from my sketchbook unless otherwise noted, and as such are rather simple and un-worked.  Hopefully though, they’ll help identify the different types and a few structures of lichens

First we learnt the difference between lichen and liverworts, and that all lichen are a fungal species living symbiotically with an algal species.  We next examined the basic structure of a lichen thallus cross-section: an upper skin or cortex with a layer of photosynthetic algae below (these are often referred to as photobiants).  Next there’s the medulla which consists of the fungus’ hyphae (sometimes called the mycobiont), and a lower skin or cortex at the base.

Cross section of lichen thallus East Tennessee Wild Flowers image

This illustration by Kris H Light comes from East Tennessee Wild Flowers’ website

Lichen are classified by their fungal partner, not the algal ones which, in many cases, are the same for many lichen species.

They also grow outwards from the centre; the oldest area of a lichen is its middle while the margins are often a different colour as these edges are the fungal hyphae reaching outward.  Only a little later do the algal photobionts follow.

The lichen shape is vital in lichen identification.  First, you get CRUSTOSE lichen which form a thin crust on their substrate.  These are the flat coloured splotches you see on stones and tree bark (and are really hard to draw!)

Lizzie Harper lichen sketch crustose form

This is an illustration of a crustose lichen, Lecanora chlarotera.

(The cups are sexual reproductive structures called apothecia, see below)

The next type is FOLIOSE which have thalli which can be lifted if you slide a finger nail under them.  They look a little like flat flakes, and sometimes have “roots” (rhizines) on their under side.

Lizzie Harper lichen sketch foliose form

Foliose lichen

The most showy type are the FRUTICOSE species which attach to the substrate at one point, then form elaborate branching shapes which stand proud of the substrate and can look like tiny trees or a mass of tangling hairs.  Their structure in cross section is circular, with the thallus layers forming around a central core rather like a gobstopper.

Fruticose lichen x section from Watching The World Blog

Image of cross section of Fruticose lichen from Watching the World Wake Up, which also has lots more great stuff on lichen.

Lizzie Harper sketch fruticose lichen

Fruticose lichen (Evernia prunastre) with foliose lichen (Parmelia sulcata) below

Below are two examples of fruticose lichen painted by Christina Hart Davies who does some of the most beautiful illustrations of lower plants I’ve seen.

Christina hart davies Ramalina lichen illustration

Fruiticose lichen Cetraria cucullata by Christina Hart Davies

Christina hart davies Ramalina lichen illustration

Fruticose lichen Ramalina fastigiata by Christina Hart davies

There are some other shapes too; PLACODIOID which are crustose at the edge and foliose at the margins;

Lizzie Harper lichen sketch placodioid form

SQUAMULOSE which consists of lots of little scales and are a variation of the crustose form; and CLADONIA which are squamulose scales with little upright feet (podetia) coming from them.  These are often very pretty; the heathland lichen which are pale green with scarlet tips are cladonia lichen.

Lizzie Harper lichen sketch cladonia form

Next, we learnt about vegetative reproduction in lichen.  The simplest form is a bit of lichen breaking off from the mother plant and growing in a new location (fragmentation).  However, lichen have two other vegetative reproductive structures too.  The first are SOREDIA.

A single soredium is a cluster of algal cells surrounded by a tuft of the associated fungal hyphae.  They’re tiny, and look like tiny fluffy spots on the thallus.  Position on the lichen margins or toward the middle of the thallus is important diagnostically.  They’re spread by wind and rain.

Lizzie Harper Lichen sketch foliose form with soredia

These are sketches of soredia on foliose lichen

Another vegetative method of reproduction is through ISIDIA.  These are tiny pegs or outcrops which pepper the surface of the thallus, and are designed to break off easily and fragment, thus allowing colonization of new habitats.

Lizzie Harper lichen sketch foliose with isidia

This is a quick sketch of the foliose lichen Melanelixia glabratula showing the little pegs of its isidia.

Lichens can also reproduce sexually, by means of APOTHECIA (which are also found in fungi).  These are cup shaped projections which have bags of spores within them.  In damp weather these bags (or asci) eject their spores into the moist air.  With age, these apothecia may become domed.  Theyre often said to resemble little cups or jam tarts since they have distinct little edges.

Lizzie Harper lichen sketch foliose form with apothecia

Lizzie Harper lichen sketch crustose from showing apothecium

Sketches of a foliose and a crustose lichen species showing apothecia

The most glorious lichen illustrations I’ve found thus far are by Clare Dalby. Unfortunately I could only find very low resolution images of the two charts she’s done for the British Lichen Society. If you have an interest in identifying or illusatrating lichen, or simply love beautiful scientific illustrations; these are well worth purchasing from the BLS.

Clare Dalby Lichen charts for BLS

Lichen charts by Clare Dalby

Having done the lichen course, I now feel I understand the morphology of lichen and thus am far better equipped to illustrate these species as I know what characteristics to look out for.  In fact, I’m rather looking forward to the next commission I get to illustrate lichen, especially if it’s a bright yellow one, a pretty cladonia, or something over-the-top and exuberant like Evernia prunastre.

Lichen Usnea subfloridana illustration by Lizzie Harper

Illustration of Usnea subfloridana by me.

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