Kupeantha (Coffeeae, Rubiaceae), a new genus from Cameroon and Equatorial Guinea

Abstract

Two new coffee relatives (tribe Coffeeae, Rubiaceae), discovered during botanical expeditions to Cameroon, are examined for generic placement, and the placement of three previously known species (Argocoffeopsis fosimondi, A. spathulata and Calycosiphonia pentamera) is reinvestigated using plastid sequence (accD-psa1, rpl16, trnL-F) and morphological data. Seed biochemistry of the new species and pollen micromorphology (only one of the two species) are also studied. Based on the plastid sequence data, the new taxa are nested in a well-supported monophyletic group that includes Argocoffeopsis and Calycosiphonia. Within this clade, three well-supported subclades are recovered that are morphologically easy to diagnose: (1) Calycosiphonia (excluding C. pentamera), (2) Argocoffeopsis (excluding A. fosimondi and A. spathulata), and (3) a clade including the above excluded species, in addition to the new species. Based on the results, Kupeantha, a new genus of five species, is described, including two new Critically Endangered taxa from the Highlands of Cameroon: Kupeantha ebo and K. kupensis. Phytochemical analysis of Kupeantha seeds reveals compounds assigned as hydroxycinnamic acid derivatives, amino acids and ent-kaurane diterpenoids; caffeine was not detected. Kupeantha is the first new genus described in tribe Coffeeae in 40 years.

Fig 1. The 50% majority consensus multiple-locus BI tree with the associated PP values and the BS values of the multiple-locus ML tree.

Only PP above 0.75 and BS values above 70% are shown. The Argocoffeopsis clade is indicated in grey.

Fig 2. SEM micrographs of pollen of Kupeantha kupensis.

A. whole grain equatorial view, showing mesocolpium, B. close-up of exine sculpturing in mesocolpial area, C. whole grain polar view, showing apocolpium, D. view of colpus and pore. All from Cheek 7882 (K).

Fig 3. Kupeantha ebo.

A. fruiting branch, B detail of stipule and supra-axillary buds, C, D. detail of stipule and stipule scar at an older nodes, E. transverse section of petiole, F. nervation, abaxial surface of leaf, G. fruit, H. fruit apex showing disc, I. Calyculi, J. opened fruit showing the two endocarps with sagittal crest surrounding the seeds, K. half fruit showing the vascularised membrane (endocarp) separating the two seeds, L. diagram of median longitudinal section of a fruit, showing the exocarp (shaded area), mesocarp (white areas), endocarp, cavities (dotted areas) and two seeds with emergent embryos, M. diagram of a median cross section of a fruit, N. dorsal view of seed, O. ventral view of seed, P. lateral view of seed, Q. median longitudinal section of seed showing the emergent embryo. A–C, E–G, I from Alvarez 11 (K); D, H, J–Q from Fenton 134 (K). Drawing by Maria G. Alvarez-Aguirre.

Fig 4. Known area of distribution of the five species of Kupeantha.

Fig 5. Field photographs of Kupeantha kupensis.

A. detail of flowers, B. detail of immature and mature fruits. Photos taken from Cheek 7882 at Mt Kupe, Cameroon, by M. Cheek.

Fig 6. Kupeantha kupensis.

A. habit, flowering branch, B. detail of stipule and node and supra-axillary buds, C. node with inflorescences, flowers in bud, D. calyculi, E. flower and calyculi, F. stamens, different views, G. gynoecium, left entire, showing disc and calyx, right, longitudinal section, H. fruits, I. fruit with a longitudinal section, showing empty locule (seed removed), J. seed, ventral surface. Scale bar: A = 4 cm; B, F, G = 7 mm; C, E, J, K = 1 cm; D = 4 mm; H = 2.5 mm; I = 2 mm. Drawn by Lucy T. Smith from Cheek 7882 (K).