Vegetative Morphology

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Vegetative Morphology

Vegetative

Morphology I

Lichen

Growth

Forms


Lichen Growth Forms

•Crustose

• Squamulose

• Foliose

• Umbilicate

• Fruticose

• Gelatinous


Evolution of Growth Forms

• These lichen growth forms do not

represent taxonomic groups

– For example: all “trees” and “shrubs” are not

related (although they have the same growth form)

– Thus all “fruticose” lichens are not related. The

fruticose growth form has evolved several times in

different groups (families)

• Growth forms (within one group) probably

arose: crustose foliose fruticose


Crustose Lichens

• Tightly attached to the substrate and

considered to be the most primitive

growth form, most species being

epilithic or epiphloeodic

– Subtypes include: powdery, endolithic,

endophloeodic, lobate, effigurate

– Some taxa may produce a distinct,

marginal hypothallus (prothallus)


Crustose

Lichens (cont.)

• Thallus structure may

be homiomerous

(unstratified) or

heteromerous

(stratified-usually

only with a cortex

and medulla)


Crustose Lichens (cont.)

Lecanora (epiphloeodic)

Acarospora (epilithic)


More Crustose Lichens

Haematomma

Porpidia


Crustose Lichens (cont.)

Crustose lichen

(Lecanora) with

an effigurate

margin


Squamulose Lichens

• Thallus composed of individual, tiny

lobes (areolae) which may be partially

free from the substrate

• Often described as overlapping or

scale-like

• If these “squamules” are attached at a

single point, the growth form is often

called peltate


Squamulose Growth Form

Psora with reproductive apothecia


Foliose Lichens

• Leaf-like, flat with lobes (lacinae) and

attached to the substrate usually with

rhizines

• May be homiomerous, heteromerous, or

gelatinous

• Heteromerous forms with upper cortex,

medulla and lower cortex

• Great diversity and common in most

environments


Foliose Lichen Section

rhizine


Upper Cortex

Medulla

Lower Cortex

SEM Section of a

Foliose Thallus


Foliose Lichens

Peltigera

Melanelia


More Foliose Lichens

Hypogymnia

Parmotrema


Umbilicate Lichens

• A foliose thallus

attached by a

single point (an

umbilicus)

• Occur on rocks,

both acidic and

basic substrates

Umbilicaria


Fruticose Lichens

• Usually described as hair-like, shrubby,

or pendulous species with rounded or

flattened lobes

• Some taxa develop a two-fold thallus

(thallus verticalis and thallus

horizontalis)

– The erect portion is often called a podetium or

pseudopodetium

– The horizontal portion is often crustose or

squamulose)


Fruticose Lichens (cont.)

• Many fruticose

species are adapted

for the acquisition of

water from the

atmosphere

• Many taxa have a

“radial” symmetry in

section


Fruticose Lichens

Letharia

Usnea


More Fruticose Lichens

Cetraria Cladonia


Gelatinous Lichens

• Thalli usually contain

cyanobacteria

• Often dark blue-green,

brown, or black in color

• Texture (when wet) of

“old Jello”

• Two most common

genera are Collema and

Leptogium

Collema


Next ……..

Vegetative Morphology II:

Anatomical Structures

of Lichen Thalli

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