The perennial Macaronesian species of Bubonium (Compositae - Inuleae).

Abstract

Six perennial Macaronesian species are recognized in Bubonium J. Hill emend. Briq.: the Cape Verdian B. daltonii (Webb) T. Halvorsen, with two subspecies, ssp. daltonii and ssp. vogelii (Webb) T. Halvorsen, and B. smithii (Webb) T. Halvorsen; and the Canarian B. intermedium (DC.) T. Halvorsen & Wikl., B. graveolens (Forssk.) Maire, with two subspecies, ssp. odorum (Schousb.) Wikl. and ssp. stenophyllum (Link) T. Halvorsen, B. schultzii (Balle) Sventenius and B. sericeum (L.f.) T. Halvorsen & Wikl. Four Mediterranean annuals are superficially treated for Macaronesia: B. aquaticum (L.) Hill, Asteriscus maritimus (L.) Less., A. hierochunticus (Michon) Wikl., and A. spinosus (L.) Sch. Bip. A key to the Macaronesian Bubonium species is provided. The chromosome number n=7 is reported for all the Bubonium species in Macaronesia; in B. graveolens ssp. odorum, B. daltonii ssp. vogelii, and B. smithii for the first time. The chromosome number n=6 is confirmed for Asteriscus maritimus. The self fertile annuals are not cross compatible with the other species. Among the predominantly self incompatible perennials internal barriers to gene exchange are weak. Only B. schultzii seems genetically isolated. Between the other perennials the crossability is complete and hybrid fertility high between species from the same archipelago, but reduced between species from different archipelagos. The present occurrence of the Canarian species B. sericeum and B. intermedium and the Cape Verdean B. daltonii and B. smithii seems relict. These frutescent endemics probably belong to an old element in the Macaronesian flora.