The Identity of Baccharis arborea L.

Abstract

Baccharis arborea was described by Linnaeus in his Mantissa Plantarum: 284 (I77i). He remarked about it: 'Habitat in Ind. orient. insulae Johannae sylvis. Koenig.' The locality was attributed to the East Indies in error; it was in fact the Island of Johanna in the Comoros. Professor T. T. Barnard, in connection with his studies of the plants collected by Koenig on his voyage to India in 1768, has raised the question of the identity of this species. In the Index Kewensis I: 258 (1875), Baccharis arborea was still maintained as a valid species and not referred to synonymy. The genus Baccharis is, however, exclusively American, and the existence of a native species in the Comoro Islands would be, to say the least, surprising. Fortunately the typification of Baccharis arborea presents little difficulty. There is a specimen in the Linnean Herbarium, sheet No. 992.3, written up as Baccharis arborea in Linnaeus's own hand. There is no other sheet so named in the Linnean Herbarium, and there can be no doubt that this specimen is in fact the holotype of Baccharis arborea. The specimen has a marked resemblance in general appearance to certain species of Vernonia, and someone has in fact written 'Vernonia' in pencil on the sheet. Baccharis and Vernonia are in different tribes of the family Compositae. Although the Linnean specimen is a reasonably good one it has no flowers and investigation of its floral characters (on which the tribal distinctions are mainly based) is thus not feasible. Although Vernonia has been revised by Humbert for the Flore de Madagascar et des Comores, 189 Compos6es (I960), the name Baccharis arborea is not mentioned there. Nevertheless the Linnean type is a very good match indeed for the sheet at Kew of Humblot 63 from the Comoros, cited as Vernonia grandis (DC.) Humbert in Fl. Madag. 189 Composees: 44 (I960) (Decaneurum grande DC., Prod. 5: 67 (1836) ), var. comorensis Humbert, l.c.: 47 (I960). The fact that Vernonia grandis var. comorensis is restricted to the Comoro Islands, according to Humbert, confirms that the Linnean specimen was, in fact, collected in the Comoros by Koenig. Professor Barnard has drawn my attention to the fact that there is not only definite corroboration of the locality but an informative collector's note in Koenig's letter to Linnaeus (Linn. Corr. Koenig to L. 26 Feb. 1769). Koenig ends his account of his visit to Johanna-'I have forgotten to tell you of the special joy that came to me on seeing a beautiful little shady tree of the class of Syngenesia; I found it in a wood on the mountains. The trunk was fully as thick as my arm and so tall that I could stand upright under its canopy. I found only two trees like this in the district. The flowers were whitish turning to yellow and resembled Conyza in their general appearance.'