The "L" stands for Linnaeus, the botanist who first named the plant. It's good to specify the Latin name (Anthemis nobilis) to make sure you're referring to this specific plant, as there are something like a half-dozen different plants commonly referred to as chamomile. Using the "L" is not necessary.

Some people are allergic to A. nobilis and related plants, which would be a reason for susceptible people to avoid them.

thank you eric_oh thats helped me loads.
another question for you if you're up for it is, in lichen, what benefits would a fungus deive from its algal partner, what does this mean. i feel such a dummy but this is a completely new subject for me. thanks again

Yes... with some plants having several common names, I think they should always go by their latin names... no mistakes there, and it helps with confusion if the plant has a 'officinalis" in it's name. I don't know which medicinal path you are taking, the only thing I can think of to answer your second question is maybe lichen has half a chemical that will mate with another to form another chemical? Like hydrogen getting together with oxygen makes water? I don't have a specific on the fungi/algae partnership.

Is the lichen question part of your homework? If so, you really should be reading your material and finding the answers. Not being mean, but you will remember the things you search out yourself and will not remember the answers you are given.

Anyway, a lichen is essentially a fungus that contains algae in its tissues. Fungus can't photosynthesize, algae can, so the fungal cells get food from the algae and the algae cells get water and minerals from the fungus.

Here is a link that might be useful: Lichen

oh wow... learn something new everyday! I am glad you said that Judy... now I know. :D