Fig.22.14. Lichens Type

Foliose lichens have somewhat leaflike thalli, which often overlap one another. They are weakly attached to the substrate. The edges are frequently crinkly or divided into lobes. Fruticose lichens may resemble miniature upright shrubs, or they may hang down in festoons from branches. Their thalli, which are usually branched, are basically cylindrical in form and are attached at one point.

It should be stressed that while lichens may be attached to trees or other plants, the majority in no way parasitize them. There are, however, a very small number of species that do produce parasitic rhizines that penetrate the cortical parenchyma cells of their hosts. Although the fungal component of a lichen usually reproduces sexually, lichens are naturally dispersed in nature primarily by asexual means. In about a third of the species, small powdery clusters of hyphae and algae called soredia (singular: soredium) are formed and cut off from the thallus in a set pattern as it grows. Rain, wind, running water, and animals act as agents of dispersal. In other lichens, specialized parts of the thallus, known as isidia, may break off or be separated by decay. Sexual reproduction in lichens is similar to that of the sac fungi except that the ascomata produce spores continuously for many years. No one has yet observed the initiation of a new thallus in nature, but it is believed that thalli arise after ascospores carried by the wind come in contact with independently living algae, germinate, and parasitize them. Lichen algae reproduce by mitosis and simple cell division.

Sac Fungi: Euascomycetidae (Lecanorales)

Graphis scripta Script Lichen

Found on hardwood trees, this crustose lichen thallus (f) has dark eruptions of apothecia (g).

Xanthoria

Found on rotten wood, the thallus (h) of this foliose lichen has apothecia composed of gray-green receptables (i) with brightly colored ascopsore layers (hymenia, j).

Physcia aipolia Blister Lichen

This foliose lichen has a white-spotted thallus (k) with apothecia emerging from the surface cortex. The fertile layer of asci (hymenium, l) is gray with a gray-green receptacle (m).

Cladonia cristatella British Soldiers

The fruticose podetium (n) arises from a squamulose thallus (o). Red apothecia (p) dot the top of the podetia.

Cladonia pyxidata Pyxie Cup

The fruiticose podetia (q) resemble pyxie cups arising from a squamulose thallus (r). Brown apothecia (s) dot the cup rims.

PLAN OF THEME STUDY:

I. Homework

TASK № 1. Using lectures and textbooks, learn basic theoretical issues.

TASK № 2. Learn English and Latin names, herbaria and demonstration table following families:

Division Fungi , Mycota:

Class Zygomycetes

Mucor mucedo

Class Ascomycetes

Saccharomyces cerevisiae

Saccharomyces vini

Candida debicans

Сlaviceps purpura

Class Basidiomycetes:

Tomes laricis

Inonotus оbliguus

Amonita caeseria

Boletus edulis

Class Fungi imperfecti, Deuteromycetes:

Aspergillus niger

Penicillium chrysogenium

Division Lichenophyta:

Cladonia rangiferina

Usnea

Cetraria islandica

Date: 2016-01-03; view: 1004