Lichen growth forms: Difference between revisions

[[Lichen]]s are [[symbiotic]] organisms made up of multiple species: a [[fungus]], one or more [[photobiont]]s (an [[alga]] and/or a [[cyanobacteria]]) and sometimes a [[yeast]]. They are regularly grouped by their external appearance – a characteristic known as their '''growth form'''. This form, which is based on the appearance of vegetative part of the lichen (its [[thallus]]), varies depending on the species and the environmental conditions it faces. [[Lichenologist]]s (thoseThose who study lichens ([[lichenologist]]s) have described a dozen of these forms: areolate, byssoid, calicioid, cladoniform, crustose, filamentous, foliose, fruticose, gelatinous, leprose, placoidioid and squamulose. Traditionally, [[crustose lichen|crustose]] (flat), [[foliose lichen|foliose]] (leafy) and [[fruticose lichen|fruticose]] (shrubby) are considered to be the three main forms. In addition to these more formalised, traditional growth types, there are a handful of informal types named for their resemblance to the lichens of specific [[genera]]. These include alectorioid, catapyrenioid, cetrarioid, hypogymnioid, parmelioid and usneoid.

== OverviewContext ==

An areolate lichen is the most common form of [[crustose lichen]].{{sfn|Hawksworth|Hill|1984|p=16}}{{sfn|Jahns|1973|p=21}} As with all crustose lichens, it has a paint-like appearance, and is inseparable from the substrate on which it grows. However, its thallus is broken into regular [[polygon|polygonal]]al sections, which can look a bit like cracked mud, flaking paint or little islands.{{sfn|British Lichen Society|ref=BLS}}{{sfn|Hawksworth|Hill|1984|p=16}} These sections, known as areolae, are surrounded by a thin layer of fungal hyphae called a [[hypothallus]]. This layer, which is usually dark, generally grows faster than the thallus which rides above it.{{sfn|Jahns|1973|p=21}} This growth form is an adaptation which allows the lichen to cope with alternating periods of wet and dry. During wet periods, the lichen can absorb water, its tissues can swell, and the cracks close.{{sfn|Hawksworth|Hill|1984|p=16}} The term "areolate" is derived from the [[Latin]] word ''areolatus'', meaning "with areolae" (the plural of a diminutive form of ''area'', meaning "halo" or "open space") combined with the Latin suffix ''-atus'', meaning "provided with" or "likeness".{{sfn|Ulloa|Hanlin|2012|p=38}}

|File:Rhizocarpon sp. (44127308692).jpg|''[[Rhizocarpon]]'' species|alt1=Rock with greenish crust, marked with myriad black lines and small raised black dots

|File:Acarospora strigata - Flickr - pellaea (15).jpg|''[[Acarospora strigata]]''|alt2=Rust-coloured rock with cracked white crust covering much of it

|File:Caloplaca maculata 113437795.jpg|''[[Caloplaca maculata]]''|alt3=Rock covered with cracked multicoloured crust: white, yellow and bright orange

|File:Roccellinastrum neglectum 91047195.jpg|''[[Roccellinastrum neglectum]]''|alt1=fuzzy white growth, like cotton wool

|File:Coenogonium sp. - Flickr - pellaea.jpg|''[[Coenogonium]]'' species|alt2=fuzzy light green growth

=== Calicioid ===

|File:Calicium viride 861877.jpg|''[[Calicium viride]]''|alt1=black stalks with flat heads, like small thin nails, rising from slanted lumpy green surface

|File:Chaenotheca brunneola 14458312.jpg|''[[Chaenotheca brunneola]]''|alt2=short black stalks with round black heads, like small dressmaker's pins, rising from a sloped, rough, white surface

|File:Cladonia furcata 105945684.jpg|''[[Cladonia furcata]]'', with branched podetia|alt1=thin, branched green twiglets growing out of small, scattered green leaves in a depression in a log

|File:Cladonia macilenta 58390907.jpg|''[[Cladonia macilenta]]'', with spike-like podetia|alt2=red-topped green tubes rising from a mound of small, green leaves

|File:Cladonia pyxidata 54677050.jpg|''[[Cladonia pyxidata]]'', with cup-shaped podetia|alt3=thick tubes with wide, cup-shaped tops rising from a mound of small, green leaves

|File:Lecanora chlarotera 105304695.jpg|''[[Lecanora chlarotera]]'', which has no prothallus|alt1=white splotch mostly covered with raised, roundish, reddish-brown disks

|File:Caloplaca marina.JPG|''[[Caloplaca marina]]''|alt2=rounded greyish rock covered in bumpy orange splotches sitting on green grass

|File:Lecidella elaeochroma Jymm.jpg|''[[Lecidella elaeochroma]]'', showing a narrow black prothallus at the edges|alt3=branch covered in smooth white crust marked with round, raised black dots and think black lines

|File:WilaBig.jpg|''[[Bryoria fremontii]]''|alt1=a thick mat of long, auburn, hairlike strands

|File:Ephebe lanata Jymm.jpg|''[[Ephebe lanata]]''|alt2=mat of short, branched, black strands against a white rock

|File:Flavoparmelia caperata 240112.jpg|''[[Flavoparmelia caperata]]''|alt2=Roughly circular lichen composed of many small, leafy, green segments

|File:Parmelia sulcata - Lindsey.jpg|''[[Parmelia sulcata]]''|alt3=Multiple lobed, green, leafy segments crisscrossed with thin white lines and tipped with burnt-looking brown ends

|File:Cladina portentosa 5510.JPG|''[[CladinaCladonia portentosa]]''

|Collema bachmanianum - Flickr - pellaea.jpg|''[[Collema bachmanianum]]''|alt1=rough, lumpy mass composed of brown circular sections edged in black

|2012-10-30 Leptogium phyllocarpum (Pers.) Mont 277066.jpg|''[[Leptogium phyllocarpum]]''|alt2=pile of round, greyish structures with bright pink centers

|Collema subflaccidum 59989135.jpg|''[[Collema subflaccidum]]''|alt3=wet green tissue, heavily and intricately folded

|File:Lepraria neglecta - Flickr - pellaea (1).jpg|''[[Lepraria neglecta]]''|alt1=powdery greenish-grey crust

|File:Chrysothrix xanthina 59817593.jpg|''[[Chrysothrix xanthina]]''|alt2=powdery sulphur-yellow crust

A placodioid lichen is a form of crustose lichen with lobed margins.{{sfn|British Lichen Society|ref=BLS}} These lobed edges, which radiate from the central part of the lichen, are its only growing sections; the central part of the lichen typically contains reproductive structures and does not expand.{{sfn|Smith|Aptroot|Coppins|Fletcher|2009|p=35}}{{sfn|Baron|1999|p=26}} The growth rates of these lobes can vary – sometimes significantly – which can lead to some lobes being overgrown by others.{{sfn|Hooker|1980|p=315}} When this happens, the overgrown lobes stop growing and are ultimately swallowed up by the expanding lichen.{{sfn|Hooker|1980|p=316}} As with other crustose lichens, placodioid lichens have a cortex on their upper surface, but not their lower one.{{sfn|Baron|1999|p=26}} This allows them to be distinguished from foliose lichens, which can be similar in appearance but have both an upper and a lower cortex.{{sfn|Baron|1999|p=27}} Crustose lichens may be both placodioid and areolate, as in, for example, ''CaloplacaVariospora flavescens''.{{sfn|Smith|Aptroot|Coppins|Fletcher|2009|p=262}} The term "placodioid" derives from the Greek ''plakós'', meaning "plaque" or "tablet", and the Latin suffix ''-oides'' – a contraction of the Greek ''oeides'', which denotes similarity.{{sfn|Ulloa|Hanlin|2012|p=482}}

|File:Variospora flavescens 232782.jpg|''[[CaloplacaVariospora flavescens]]''|alt1=a dark rock with an orange splotch which has lobed edges and a white centre sprinkled with raised orange dots

|File:Moonglow Lichen - Flickr - pellaea.jpg|''[[Dimelaena oreina]]''|alt2=a rough pink rock with a pale green splotch with lobed edges and a darker centre studded with tiny, black-centred disks

|File:Lecanora valesiaca 728066.jpg|''[[Lecanora valesiaca]]''|alt3=a bumpy white splotch with downcurved lobes at the edges and a cluster of raised, orange-centred disks in the middle

|File:Omphalina hudsoniana.jpg|''[[Lichenomphalia hudsoniana]]''|alt1=tightly packed, leafy green growth with a few small, flat, emergent, yellowish-orange mushrooms

|File:Normandina pulchella 130615717.jpg|''[[Normandina pulchella]]''|alt2=scattered small green leaves, many shaped like human ears growing among moss fronds

|File:Tree Stipplescale (4752735810).jpg|''[[Placidium arboreum]]''|alt3=a solid mass of tiny, flattened, overlapping, greenish leaves

In addition to the above forms, lichenologists have named a handful of informal growth forms for their resemblance to members of particular genera. Each of these is a subset of one of the growth forms described above. For an indication of what they look like, see the gallery below.

Catapyrenioid lichens were historically members of the genus ''[[Catapyrenium]]''; many have now been moved to other genera within the family [[Verrucariaceae]]. They are squamulose and lack algae in their [[hymenium]] – the part of the fruiting structure where spores are formed. Their simple [[ascospores]] have no partitions.{{sfn|Breuss|2010}}

* {{cite book |last1=Büdel |firstfirst1=B. |last2=Scheidegger |first2=C. |editor-last=Nash |editor-first=Thomas |chapter=Thallus morphology and anatomy |title=Lichen Biology |year=1996 |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-45368-4}}

* {{cite journal |last=Kantvilas |first=Gintaras |title=A new byssoid lichen genus from Tasmania |date=May 1996 |journal=The Lichenologist |volume=28 |issue=3 |pages=229–237 |doi=10.1006/lich.1996.0020 |s2cid=85573550 |url=http://nhm2.uio.no/botanisk/lav/RLL/PDF2/Lichenologist/28/28_229-237.pdf|archive-url=https://web.archive.org/web/20141028140630/http://nhm2.uio.no/botanisk/lav/RLL/PDF2/Lichenologist/28/28_229-237.pdf |archive-date=3128 October 20222014}}

* {{cite journal |first1=O. L. |last1=Lange |first2=J. |last2=Belnap |first3=H. |last3=Reichenberger |title=Photosynthesis of the cyanobacterial soil-crust lichen ''Collema tenax'' from arid lands in southern Utah, USA: role of water content on light and temperature responses of CO2 exchange |journal=Functional Ecology |volume=12 |issue=2 |date=April 1998 |pages=195–202 |doi=10.1046/j.1365-2435.1998.00192.x |doi-access=free |bibcode=1998FuEco..12..195L }}

* {{cite journal |first1=Yolanda F. |last1=Wiersma |first2=R. Troy |last2=McMullin |title=Are calicioids useful indicators of boreal forest continuity or condition? |journal=Biodiversity and Conservation |volume=31 |issue=5–6 |date=May 2022 |pages=1647–1664 |doi=10.1007/s10531-022-02418-5|bibcode=2022BiCon..31.1647W |s2cid=248308797 }}