Editing Lichen (section)

=== Growth forms ===
{{Main|Lichen growth forms}}
Lichens grow in a wide range of shapes and forms; this external appearance is known as their [[morphology (biology)|morphology]]. The shape of a lichen is usually determined by the organization of the fungal filaments.<ref name=MSULB/> The nonreproductive tissues, or vegetative body parts, are called the ''[[thallus]]''. Lichens are grouped by thallus type, since the thallus is usually the most visually prominent part of the lichen. Thallus growth forms typically correspond to a few basic internal structure types. [[List of common names of lichen genera|Common names for lichens]] often come from a growth form or color that is typical of a lichen [[genus]].

Common groupings of lichen thallus growth forms are:
# [[fruticose lichen|fruticose]]<ref name="LNAILV" /><ref name=ASLGPZ/><ref name=Dobson/> – growing like a tuft or multiple-branched leafless mini-shrub, upright or hanging down, 3-dimensional branches with nearly round cross section ([[terete]]) or flattened
# [[foliose lichen|foliose]]<ref name="LNAILV" /><ref name=ASLGPZ/> – growing in 2-dimensional, flat, leaf-like lobes
# [[crustose lichen|crustose]]<ref name=ANBGLG>{{cite web |url=http://www.anbg.gov.au/glossary/webpubl/lichglos.htm |title=Lichen Glossary |last=Galloway |first=D.J. |date=13 May 1999 |archive-url=https://web.archive.org/web/20141206070827/http://www.anbg.gov.au/glossary/webpubl/lichglos.htm |archive-date=6 December 2014 |publisher=Australian National Botanic Gardens}}</ref><ref name="LNAILV" /><ref name=ASLGPZ/> – crust-like, adhering tightly to a surface ([[substrate (biology)|substrate]]) like a thick coat of paint
# [[Squamulose lichen|squamulose]]<ref name=Dobson/> – formed of small leaf-like scales crustose below but free at the tips
# [[Leprose lichen|leprose]]<ref name=ASLTT/> – powdery
# [[Gelatinous lichen|gelatinous]] – jelly-like
# [[filamentous lichen|filamentous]] – stringy or like matted hair
# [[Byssoid lichen|byssoid]] – wispy, like [[teased wool]]
# structureless

There are variations in growth types in a single lichen species, grey areas between the growth type descriptions, and overlapping between growth types, so some authors might describe lichens using different growth type descriptions.

When a crustose lichen gets old, the center may start to crack up like old-dried paint, old-broken asphalt paving, or like the polygonal "islands" of cracked-up mud in a dried lakebed. This is called being [[rimose]] or [[areolate]], and the "island" pieces separated by the cracks are called areolas.<ref name="LNAILV" /> The areolas appear separated, but are (or were){{citation needed|date=October 2014}} connected by an underlying [[prothallus#In lichens|prothallus]] or [[hypothallus]].<ref name=ASLTT/> When a crustose lichen grows from a center and appears to radiate out, it is called crustose placodioid. When the edges of the areolas lift up from the substrate, it is called [[squamulose]].<ref name=VMBMLF/>{{rp|159}}<ref name=Dobson/>

These growth form groups are not precisely defined. Foliose lichens may sometimes branch and appear to be fruticose. Fruticose lichens may have flattened branching parts and appear leafy. Squamulose lichens may appear where the edges lift up. Gelatinous lichens may appear leafy when dry.<ref name=VMBMLF/>{{rp|159}}

The [[thallus]] is not always the part of the lichen that is most visually noticeable. Some lichens can grow ''inside'' solid rock between the grains ([[endolithic lichen]]s), with only the sexual fruiting part visible growing outside the rock.<ref name="LNAILV" /> These may be dramatic in color or appearance.<ref name="LNAILV" /> Forms of these sexual parts are not in the above growth form categories.<ref name="LNAILV">Lichen Vocabulary, Lichens of North America Information, Sylvia and Stephen Sharnoff, [http://www.lichen.com/vocabulary.html] {{Webarchive|url=https://web.archive.org/web/20150120063843/http://www.lichen.com/vocabulary.html|date=20 January 2015}}</ref> The most visually noticeable reproductive parts are often circular, raised, plate-like or disc-like outgrowths, with crinkly edges, and are described in sections below.