Lukea gen. nov. (Monodoreae-Annonaceae) with two new threatened species of shrub from the forests of the Udzungwas, Tanzania and Kaya Ribe, Kenya

Abstract

SummaryA new genus, Lukea Cheek & Gosline (Annonaceae), is erected for two new species to science, Lukea quentinii Cheek & Gosline from Kaya Ribe, SE Kenya, and Lukea triciae Cheek & Gosline from the Udzungwa Mts, Tanzania. Lukea is characterised by a flattened circular bowl-shaped receptacle-calyx with a corolla of three free petals that give the buds and flowers a unique appearance in African Annonaceae. Both species are extremely rare shrubs of small surviving areas of lowland evergreen forest under threat of habitat degradation and destruction and are provisionally assessed as Critically Endangered and Endangered respectively using the IUCN 2012 standard. Both species are illustrated and mapped. Material of the two species had formerly been considered to be possibly Uvariopsis Engl. & Diels, and the genus Lukea is placed in the Uvariopsis clade of the Monodoreae (consisting of the African genera Uvariodendron (Engl. & Diels) R.E.Fries, Uvariopsis, Mischogyne Exell, Dennettia Baker f., and Monocyclanthus Keay). The clade is characterised by often conspicuous, finely reticulate quaternary nervation, incomplete or absent connective shields (in Annonaceae the connective shield is usually complete) and free petals (except in some Uvariopsis). Morphologically Lukea is distinct for its broad, turbinate, fleshy pedicel, a potential synapomorphy within Monodoreae. It appears closest morphologically to the West African monotypic Monocyclanthus, since it shares a trait unusual in the Annonaceae: the calyx in both genera forms a shallow bowl (calyx lobes are absent or vestigial), barely enclosing the base of the petals at anthesis, which persists, living and green, in the mature fruit. However, on recent molecular phylogenetic evidence, Lukea is sister to Mischogyne and the two split c. 20 million years BP, while Monocyclanthus is sister to Dennettia. The placement of Lukea within the Uvariopsis clade is discussed.