Taxonomic history The population was discovered in the 1950s and assumed to be a form of
Dudleya greenei, a plant also occurring on the island which is similar but larger and contains the same number of
chromosomes. Reid Moran regarded it as
Dudleya greenei forma
nana in an unpublished description. In the publication of the
Dudleya and Hasseanthus Handbook,
Paul H. Thomson separated the plant as a distinct species,
Dudleya nana (1988)
, based on Moran's description and the cultivated "White Sprite" variety. However, Thomson's description was not valid. He failed to accurately place the collection number, collector, collection date, type specimen, or the location of a type specimen in a herbarium, which meant that Thompson's description did not constitute a valid publication according to the
International Code of Botanical Nomenclature. In 1997, botanist
Stephen W. McCabe gave the species a proper description as
Dudleya gnoma. The species was placed in the subgenera
Dudleya. Although it is included in subgenus
Dudleya, some of the petals approach a degree of spreading seen mostly in subgenus
Stylophyllum plants like
Dudleya traskiae. The habit of the plants to grow on flat areas and in shallow soil is also similar to the subgenus
Hasseanthus. The overwhelming majority of the other characteristics, including the average petal altitude, broad leaf bases, and evergreen nature, does place it in subgenus
Dudleya.
Characteristics This plant differs from
Dudleya greenei, which it was originally assigned to, in a number of different ways. The rosettes of
D. gnoma are much smaller, and the leaves are shaped triangular to triangular-ovate, as opposed to the larger, non-triangular and variously shaped leaves of
D. greenei. The
bracts,
flowers, and
pedicels of
D. gnoma are all smaller and shorter than in
D. greenei. In
D. gnoma, the base of the pedicel of the first flower is 2 to 4 mm from the base of the lowest
cincinnus. In
D. greenei, the base of the pedicel of the first flower is usually 0 mm from the base of the first cincinnus, as it is directly attached to it. In
D. gnoma, there are usually two branches to the inflorescence, and the two infrequently rebranch after. In
D. greenei, there are usually three branches in the inflorescence, and they may rebranch and ascend. In horticultural or lush, rainy conditions,
D. gnoma may produce additional branches on the inflorescence. The habitat of both species is also different.
D. gnoma is found on shallow soils in flat areas, while
D. greenei is found on cliff faces in canyons or seacliffs. Even the smallest flowering forms of
Dudleya greenei are distinguished from
D. gnoma, because they have blunter leaf apices and leaves that are oblong and more round in cross section. == Distribution and habitat ==