Big-Leaf Periwinkle
Vinca sp.
Photographed on the grounds of the Nairobi Arboretum, Kenya, November, 2012.
From Wikipedia: An evergreen trailing vine, spreading along the ground and rooting along the stems to form dense masses of groundcover individually 2-5 m across and scrambling up to 50-70 cm high. The leaves are opposite, nearly orbicular at the base of the stems and lanceolate at the apex, 3-9 cm long and 2-6 cm broad, glossy dark green with a leathery texture and an entire but distinctly ciliate margin, and a hairy petiole 1-2 cm long. The flowers are hermaphrodite, axillary and solitary, violet-purple, 3-5 cm diameter, with a five-lobed corolla. The calyx surrounding the base of the flower is 10–17 millimetres long with hairy margins. This plant is native in northern Africa and might be close enough to it's origin to be considered native to Kenya.