thumbnail|[[Polyscias cutispongia (=Gastonia cutispongia)]]
Gastonia is a formerly accepted genus of 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). 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. 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. 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. 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. 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. 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.