Al wrote:
I wonder why Kew authorities have decided to accept a name published only in
1970 over one published first in 1827. The acceptance of the oldest
published name is the rule and exception to it are generally explained
someplace to somebody in writing.
(snip)
Zygopetalum mackayi Hook., Bot. Mag. 54: t. 2748 (1827).
Zygopetalum maculatum (Kunth) Garay, Orquideologia 5: 189 (1970).

Hi Al,

See my previous response to Pat. I think the key is that the 1970 name
is Zygopetalum maculatum (Kunth) Garay, not Zygopetalum maculatum
Garay. Kunth apparently named the plant Dendrobium maculatum in 1816,
beating Zygopetalum mackayi by 11 years. Back then, most epiphytic
orchids were shoehorned into a few genera, so it is the "maculatum"
epithet that is significant not the odd use of "Dendrobium." IIRC,
species epithets are usually conserved when a species is moved to a new
genus, so "maculatum" is the oldest published species epithet in this
case.

Presumably, Garay pointed out that "maculatum" is the oldest name for
the plant in question and to explicitly linked it to Zygopetalum.

Nick