Cyathula guineensis (Amaranthaceae), a new and endangered species from the Republic of Guinea.

The new species Cyathula guineensis (Amaranthaceae), from Faranah and Kankan Regions of northern and central Guinea, is described and illustrated. This new species is assessed as globally Endangered, as it faces a range of threats at its two known locations and is estimated to have a small global population size, with fewer than 250 mature individuals within each of its two known sub-populations. Its taxonomic affinities are discussed, in particular with regard to the sympatric Cyathula pobeguinii Jacq.-Fél. and with C. mollis C.C.Towns. from the Central African Republic, both of which share with the new species modified sterile flowers that are not hooked or spiny, these instead are tepal-like or bracteolate. The generic placement of these species is discussed in light of recent molecular phylogenetic evidence that resolves Cyathula as being polyphyletic within the “achyranthoid” clade of Amaranthaceae and which has resulted in a proposal to modify and expand the circumscription of the genus. Finally, the role of the modified, sterile flowers in aiding epizoochory in Cyathula guineensis is discussed.