EXTRA lichen
Grouping lichens:
By their appearance the lichens can be grouped into three main categories of growth forms,
• Crustose lichens: The thallus in crustose lichen is closely attached to the substratum without leaving any free margin. The thallus usually lacks lower cortex and rhizines (root like structure). Such lichens are collected along with their substratum for the detailed study.
• Foliose lichens: They are also called as leafy lichens. The thallus in this case is loosely attached to the substratum at least at the margin. Such lichens are collected by scraping them from the substratum.
• Fruticose lichens: Here the lichen thallus is attached to the substratum at one point and remaining major portion is either growing erect or hanging. The lichen usually appears as small shrub or bush and easy to collect with hand.
There are few intermediate categories of growth forms such as,
• Leprose lichens: The leprose lichen is powdery or granular and does not form smooth thallus.
• Placodioid lichens: In this case the lichen thallus is closely attached to the substratum at centre and lobate or free at the margin, but lack rhizines.
• Squamulose lichens: Here the lichen thallus is in the form of minute lobes, having dorsiventral differentiation. The rhizines may be present or absent. This is a form intermediate between crustose and foliose.
• Dimorphic lichens: In case of dimorphic lichens single thallus has the characters of both foliose/ squamulose and fruticose lichens. The squamules are the primary thallus, which bears erect body of fruticose lichen, the secondary thallus.
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