Aspects of the taxonomy of the Kalanchoe daigremontiana species complex (Crassulaceae subfam. Kalanchooideae) and associated interspecific hybrids in southern Madagascar, with the description of a new nothospecies, K. ×descoingsii (=K. laetivirens × K. tubiflora)

Species included in Kalanchoe [subg. Bryophyllum] sect. Invasores (Crassulaceae subfam. Kalanchooideae), an infrageneric group naturally restricted to Madagascar, are, as the section name suggests, known to have several reproductive mechanisms that enable their successful establishment and spread in suitable climates in, and well away from, their natural habitats. Four species, which are particularly invasive, produce bulbils constitutively and copiously on dedicated pedestals that adorn their leaf margins or are concentrated towards the leaf tips, in the case of K. tubiflora. These species are: the predominantly pink-flowered K. daigremontiana, K. laetivirens, and K. sanctula, all with stem-peduncle transitions that give rise to distinct inflorescences, as well as K. tubiflora, which produces variously coloured inflorescences that indistinctly transition from the stem into a peduncle. Despite their apparent preferential, but not exclusive, reliance on asexual reproduction, several nothospecies involving these species have been described from southern Madagascar, and K. ×houghtonii, an artificially raised hybrid, has become naturalised on all continents bar Antarctica. Aspects of the taxonomy of these species and nothospecies are dealt with and arguments are presented in support of recognising K. laetivirens as a species, rather than as a nothospecies. The types of the names K. laetivirens and K. sanctula are no longer extant; both names are here neotypified. The geographical occurrence in Madagascar of K. laetivirens, and possibly K. ×houghtonii (=K. daigremontiana × K. tubiflora, known to have been artificially and independently produced in the USA and continental Europe), are discussed in detail. Kalanchoe ×descoingsii (=K. laetivirens × K. tubiflora) is described as a new nothospecies that was discovered in Madagascar where both parents grow sympatrically as a result of human activity.