Gastonia (plant)

Gastonia is a formerly accepted genus of flowering plants in the ivy and ginseng family, Araliaceae. It had been known as an unnatural group, but was recognized as late as 2010, when its nine species were distributed to four different subgenera of the large genus "Polyscias". Because the genus "Gastonia" is now obsolete, its species are herein referred to by their names in "Polyscias".
The species that constituted "Gastonia" are mostly island endemics, with Madagascar and New Guinea being the largest land masses on which any of them naturally occur. "Gastonia" had a disjunct distribution, with three species from the Seychelles, three more from the Mascarenes, one from Madagascar and the Comoro Islands, and two distributed from Malesia to the Solomon Islands.
"Gastonia" is a genus of small to large size trees. It shares with related genera, the lack of an articulation on the pedicel, below the flower. It is distinguished from "Reynoldsia", "Munroidendron", and "Tetraplasandra" by the radiating style arms that persist on the fruit.
Species.
Listed below are the nine species placed in "Gastonia" by Frodin and Govaerts (2003). Names in "Polyacias" are from Lowry and Plunkett (2010).
Notes on selected species.
"Polyscias spectabilis" is from New Guinea and the Solomon Islands. It sometimes exceeds in height, and is the tallest member of Araliaceae. Like most members of "Polyscias", "P. spectabilis" is sparingly branched, sometimes even palm-like in form, at least when young. Mature individuals of "P. spectabilis" are sometimes unbranched for 3/4 of the height of the tree. Hermann Harms erected the monotypic genus "Peekeliopanax" for it in 1926, but was not followed by other authors.
The type species for "Gastonia" is "Gastonia cutispongia" (now "Polyscias cutispongia"). It is a tall, smooth tree with spongy bark. It is native to Réunion and sometimes planted there, but it has become very rare.
"Polyscias maraisiana" is endemic to Mauritius and was cultivated in Europe in the 19th century, but has not been seen there since that time. It was considered exotic on account of its strikingly heteroblastic leaves.
"Polyscias maraisiana" has been the subject of some nomenclatural instability. In 1984, Wessel Marais separated it from "Gastonia cutispongia" as "Gastonia mauritiana". In 2003, it was shown that the correct name for this species was "Gastonia elegans" because it had first been described in 1866 as "Terminalia elegans". This description was a large and unexpected taxonomic error because "Terminalia" is in the Myrtalean family Combretaceae. In 2010, when this species was transferred to "Polyscias", the specific epithet had to be changed again because the names "Polyscias mauritiana" and "Polyscias elegans" already existed. The latter two are in the "Polyscias" subgenera Grotefendia and Tieghemopanax, respectively.
The most widespread and variable of the species in the former "Gastonia" is "Polyscias serratifolia". It ranges thru most of Malesia and from there to the Solomon Islands. Some of its varieties have been named as separate species and placed in other genera, such as "Arthrophyllum" and "Tetraplasandra". These were united into one species by , as "Gastonia papuana" in 1970, and as "Gastonia serratifolia" in 1979.
History.
Quattrocchi states that "Gastonia" was "named after Gaston d'Orléans, 1608-1660, a patron and promoter of botany and floriculture". The name was originated by Philibert Commerson, but validated later, in 1788, by Jean-Baptiste Lamarck in "Encyclopédie Méthodique.
Lamarck gave a detailed description of the species that he named "Gastonia cutispongia". He named another species, but gave it only a cursory description. No one today is really sure of what the other species was. Some authors believe that it was not even a member of Araliaceae.
Other species were added to "Gastonia" in the 19th century. In 1898, Hermann Harms transferred what is now "Polyscias sechellarum" to "Gastonia" in a landmark monograph on Araliaceae in Die Natürlichen Pflanzenfamilien.
William Raymond Philipson gave "Gastonia" its modern definition in 1970. He included Malesian species that had been in "Tetraplasandra", thus restricting that genus to the Hawaiian Islands. He also reduced the monotypic genera "Indokingia" ("Polyscias crassa") and "Peekeliopanax" ("Polyscias spectabilis") into synonymy under "Gastonia".
William Botting Hemsley had named "Indokingia" in 1906 in Hooker's Icones Plantarum. "Peekeliopanax" was a name that Hermann Harms had applied to a flowering specimen in 1926. A few years later, he placed a fruiting specimen of the same species under "Gastonia".
In 2003, a checklist and nomenclator was published for Araliaceae by Kew Gardens. Nine species were recognized therein for "Gastonia". The genus was described as "generalized, altho in details, it is quite varied". Since that time, molecular phylogenetic studies, based on DNA sequences, have shown that "Gastonia" was polyphyletic. These studies have shown that biogeography is strongly correlated with relationships in Araliaceae.
In 2010, the genus "Polyscias" was expanded from about 100 species to 159. The number of species in "Polyscias" will be around 250 when the undescribed species are published. Six genera ("Arthrophyllum", "Cuphocarpus", "Gastonia", "Reynoldsia", "Munroidendron", and "Tetraplasandra") were placed in synonymy under "Polyscias". In accordance with the phylogenetic studies of DNA, "Polyscias" was divided into 11 subgenera (Polyscias, Grotefendia, Maralia, Arthrophyllum, Cuphocarpus, Tetraplasandra, Eupteron, Sciadopanax, Tieghemopanax, Indokingia, and Palmervandenbroekia) and seven species were left incertae sedis.
The nine species that had been in "Gastonia" went to four different subgenera of "Polyscias"; three species went to Grotefendia, three more to Indokingia, two to Tetraplasandra, and one to Maralia.
"Polyscias cutispongia", "Polyscias maraisiana", and "Polyscias rodriguesiana" are endemic to Réunion, Mauritius, and Rodrigues, respectively. The latter two were separated from "P. cutispongia" in 1984. They are in "Polyscias" subgenus Grotefendia, which comprises 15 species, all from the Mascarene Islands. The type species for "Polyscias" subgenus Grotefendia is "Polyscias repanda".
"Polyscias" subgenus Grotefendia contains "Polyscias cutispongia", the type species for "Gastonia". If the subgenus Grotefendia were to be raised to the taxonomic rank of genus, the name "Gastonia" would have priority over Grotefendia, according to the ICNAFP.
"Polyscias crassa", "Polyscias sechellarum", and "Polyscias lionnetii" are all from the Seychelles, with "Polyscias lionnetii" being very rare and restricted to the island of Mahé. These are the only species of "Polyscias" in the Seychelles, and together, they constitute "Polyscias" subgenus Indokingia. "Polyscias seychellarum" is an orthographical variant of "Polyscias sechellarum". "Polyscias sechellarum" was divided into three varieties in 1987, but some authors have declined to recognize them until further studies can be done on this species.
"Polyscias duplicata" (formerly "Gastonia duplicata") is in "Polyscias" subgenus Maralia. Maralia is, by far, the largest subgenus of "Polyscias", with about 115 species. Most of them, like "Polyscias duplicata", are endemic to Madagascar.
"Polyscias serratifolia" and "Polyscias spectabilis" are now in "Polyscias" subgenus Tetraplasandra. This is a wide-ranging subgenus of 21 species. Eleven species are endemic to Hawaii, and ten others are distributed in a large area that includes Malesia and extends eastward to Tahiti.
Sources.
Gregory M. Plunkett, Jun Wen, Porter P. Lowry II, Murray J. Henwood, Pedro Fiaschi, and Anthony D. Mitchell. accepted, undated. Araliaceae, pages ??. In: Klaus Kubitzki (editor); ?? (volume editor). "The Families and Genera of Vascular Plants" volume ??. Springer-Verlag: Berlin; Heidelberg, Germany. ISBN ??