The following points highlight the two main thallophytes found in lichens. The thallophytes are: 1. Parmelia (Foliose Ascolichen) 2. Dictyonema (= Cora) (Basidiolichen).
Thallophytes # 1. Parmelia (Foliose Ascolichen):
Thallus is leaf-like, and attached to the substratum by a small portion of the thallus. Characteristic cup-shaped ascocarps (i.e., apothecia) are scattered on the mature central part of the thallus.
A cross-section of the thallus shows internal differentiation of 4 zones-uppermost compact hyphal layer, i.e., upper cortex; then algal layer which possesses algal cells intermingled with loose hyphal zones; compactly arranged hyphal medulla zone and lastly the lower cortical hyphal zone with rhizomes.
It shares the characters of the parent thallus in colour and consistency. It is typically cup or disc-shaped. In T.S. it shows a hymenial layer with asci and paraphyses lining the inner surface of the cup.
It is club-shaped and slender with 8 ascospores.
It is bi-celled, elliptical and light coloured (Fig 4.1).
Presence of symbiotic thallus association (i.e., an algae and a fungus forming the thallus).
Fungal component belongs to ascomycetes and ascocarp formed as reproductive structure.
SUB CLASS: ASCOLICHENS
Fruit-body apothecial type.
Fruit-body apothecial type, apothecia cup-shaped with hymenial layer lining the inner face of the cup.
Hymenial layer with asci and paraphyses lining the inner surface of the cup.
Ascospores bi-celled, elliptical and light-coloured, ascus 2-8 spored.
Thallophytes # 2. Dictyonema (= Cora) (Basidiolichen):
Thallus is membranous and adheres to the stem bark with conspicuous bracket-shaped basidiocarp as fruit-body.
The thallus has centrally located algal layer surrounded on both sides by compactly arranged fungal hyphae.
It is like those of bracket fungi. A T.S. through basidiocarp shows the following layers – upper hyphal layer, algal layer, medulla zone and lower fertile hyphal zone with basidium and basidiospores.
It is tubular and sterigmatic (4 in number) and intermingled with paraphyses.
Basidi-spore – It is small and ovoid in shape (Fig 4.2).
Presence of symbiotic thallus association (i.e., algal and fungal association).
Fungal component belongs to Basidiomycetes and produces basidiocarp.
SUB CLASS: BASIDIOLICHENS
Fruit body gymnocarpous, hymenium unilateral or amphigenous; sterigmata relatively small.
Fruit body typically cobwebby, membranous, leathery, hymenophore warty, spores globose to ellipsoidal.
Thallus membranous and adheres to the stem bark with conspicuous bracket-shaped basidiocarp as fruit body.
GENUS: DICTYONEMA (=CORA)