David Hershey schreef
You seem to be coming around to my viewpoint when you state that
"Frequency does not necessarily come into it." Iapacho can be a common
name even if used infrequently as I have been arguing.

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Frequency applies to many things. When using OCR to convert a scan to actual
text it is not uncommon to substitute "I" for "l". There are also some
people who when writing or editing text make errors frequently. Some later
mend their ways but others never learn.
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It is not really clear what you mean by "status of a common name".

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Webster says of "status": "1 State, condition, or relation. 2 Relative
position or rank [L 'stare' to stand]"
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If you mean whether it is considered the preferred common name for that
species in books or databases then that is decided by the author(s) of
the book or database on whatever arbitrary criteria they decide to
use. However, an author(s) of a book or database on plant taxonomy,
horticulture or gardening often makes up common names that then become
added to any compilation of common names for that species. Many common
names do not originate in a lay community. Many are created by plant
taxonomists which was one of Dr. Weber's complaints:
http://www.ou.edu/cas/botany-micro/ben/ben109.html

Hortus Third applied, or misapplied, the name devil's backbone as the
only common name, and therefore preferred common name, for Kalanchoe
daigremontiana. However, Hortus Third also says devil's backbone is
the last of eight common names for Pedilanthus tithymaloides. It seems
that devil's backbone is actually the most frequently used common name
for P. tithymaloides in English language gardening literature.
However, devil's backbone has become the de facto preferred common
name for K. daigremontiana because a lot of authors use Hortus Third
for a source of common names.

Possibly because it came into cultivation in the US rather recently in
the 1930s, not a lot of common names seem to have been applied to K.
daigremontiana. One was mother of thousands which was also applied to
other Kalanchoe species and Saxifraga stolonifera. Apparently, none of
K. daigremontiana's common names from Madagascar, if any, followed it
into cultivation in English speaking countries.

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Indeed, Hortus Third has been around a long time
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Interestingly, mother of thousands is the USDA Plant Database's only
common name for Soleirolia soleirolii yet Hortus Third lists baby's
tears first of its eight common names and does not list mother of
thousands or helxine. Baby's tears is probably the most widely used
common name for that species in English language gardening literature.
Hessayon's influential book, House Plant Expert, gives the preferred
common name of helxine with mind-your-own-business as his second
choice and baby's tears third. Standardization of plant common names
doesn't work when major authorities disagree.

You say "There are rules for common names, just not a single set."
What are some examples? The only thing close to "rules" seem to be
books or databases that suggest a preferred common name (e.g. Hortus
Third) or standardized common name (e.g. USDA Plant Database, 1942
book Standardized Plant Names) for each species. However, they are not
really rules because they give no details of how they determined the
preferred or standardized names.

Your Webster's definition of "name" does not completely fit plant
common names because it limits "name" to one, i.e. "the distinctive
appelation".

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Webster "common": "1 Not unusual; ordinary; regular" and "4 Widespread;
general: 'common' knowledge"
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It is a fact that there are often many common names for a
plant species.

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Each in its own world.
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More relevant might be Webster's definition of
"vernacular" as "applied to a plant or animal in the common native
speech as distinguished from the Latin nomenclature of scientific
classification."

Your "name" definition also does not eliminate iapacho or buried-fruit
plant as common names because it says nothing about the size of the
population that knows the plant by that term. Many individuals have
one, or more, pet names for their spouse that is known by just that
couple, yet each pet name still is a name.

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as you say, a "pet name"
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It is probably true many common names arose when travel and
communication were not so good, however, you'd have to do some study
to determine the time and place of origin of the many common names for
Cymbalaria muralis.

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Likely somebody already did that, at one time or another
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I would not be surprised if some of the common
names for Cymbalaria muralis were misapplications of names for other
plants or were inventions by authors. The exact origins of many common
names can probably never be known with certainty.

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Exact origins may be found in some cases. A lot depends on the name and on
existing tradition of linguistic research. Also on what you mean by
"certainty".
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I see no justification for your view that bois d'arc and bodark
represent a more "appropriate" example of a degenerate common name.

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I cannot help what you do and do not see.

Compared to [quote]
"Common name ... may be a degenerate form of another word, as markery is of
mercury."
a reference to a plant that made a recent appearance in this list looks
"more appropriate" to me. Aso it is a nice clean derivation, which was
'degenerated' for a logical reason
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It is probably a less typical example because it involves an English
corruption of a French name. Bailey's mercury and markery are
apparently common names for Toxicodendron radicans or Rhus radicans,
better known as poison ivy. Hortus Third also list markry as a common
name for Rhus radicans.

Other possible degenerate common names include:

heltrot and eltrot for Heracleum sphondylium (possibly both
degenerated from heeltrot applied to Pastinaca sativa)
coriander and coryander for Coriandrum sativum

It might be more desirable for scientists to refer to common names as
unscientific names in order to get the point across that they are not
as desirable as scientific names.

David R. Hershey

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Would be both overkill and misleading. Common names are not necessarily
"unscientific", although they might be
PvR