Let us assume there is a lichen called "Bloggsia vulgaris". So far as I know, there isn't, but we are pretending, okay?
Someone decides that within the species there is an entity, quite possibly a geographical race, that merits recognition as a separate subspecies. This is given its own Latin name, say "Bloggsia vulgaris subsp. arctica", with its own published Latin description and type specimen. At the moment of publication, without any other action required, that part of the species that still corresponds with the original description and type specimen then becomes "Bloggsia vulgaris subsp. vulgaris". This is called the "nominate subspecies".
So this Bloggsia vulgaris is defined by an original, published Latin description and is based on a specimen (the 'type specimen') that has been carefully preserved in a herbarium. (This may not always be the case for old names, but we are still pretending.)
Now we have a lichenologist who is recording and comes across Bloggsia vulgaris in a region where both subspecies occur. However, he simply records the species and doesn't take the identification to subspecies. This might be because:
• his book doesn't give the two subspecies, so he is unaware of them;
• he cannot decide which subspecies it is so just records the species;
• he finds that in that area, the subspecies seem to merge and his specimen cannot be assigned to a subspecies;
all legitimate reasons.
Sometime later his lists are passed to Tracey, who has the task of putting these records onto a database. (If you object to the gender assignment here, think of her as "Tom".) Now Tracey (or Tom) has an IQ not greatly different from that of the potted plant on her desk. So when she (or he) comes to the record of Bloggsia vulgaris, she sees there are two subspecies, notes that it hasn't been recorded as "Bloggsia vulgaris subsp. arctica", so she assumes (without any checks) that the record is for "Bloggsia vulgaris subsp. vulgaris". Our original lichenologist's careful avoidance of recording the subspecies has been ignored.
It may be that subsp. vulgaris is very rare in the area and nearly all populations are subsp. arctica, but our lichenologist is now in the database as having recorded subsp. vulgaris. In the fullness of time, the database records are passed on to the National Biodiversity Network (NBN), which has limited error-checking.
This "nominate subspecies problem" is a widespread problem in biological databases; I have repeatedly seen it happen to my own flowering-plant records where I have had good reason (intermediates, wrong time of the year, ...) to avoid recording subspecies, but someone else, who never saw my plants, has presumed to know better than me what I saw.
Regarding lichens, I note that some definitely spurious records for Cladonia uncialis subsp. uncialis, field records supposedly made before the species was ever split, have actually vanished from the NBN maps, as have some dubious JNCC records for Cladonia crispata var. crispata. Even so, essentially unreliable NBN maps include those for:
• Cladonia uncialis subsp. uncialis
• Cladonia arbuscula subsp. arbuscula (though there are additional problems of changing taxonomy here)
• Cladonia crispata var. crispata.
• Cladonia ciliata var. ciliata is probably also significantly over-recorded.
When I become World Dictator (it is on my to-do list, though there are unresolved procedural matters), I intend a reasonably benign rule. However, Tracey will be amongst the first in front of the firing squads.
She will not be alone though ...
There are also those who take a record from a site that may be 1km2 or more in size, and insert, i.e. make up, i.e, falsify, a six figure grid reference. Sometimes they call it a "centroid", which is a synonym for "deliberate lie". Their time also will come!