Duvalia

Duvalia is a succulent plant genus in the subfamily Asclepiadoideae, in the family Apocynaceae (dogbane).

The genus was first described in 1812, named after the French physician and botanist Henri-Auguste Duval (1777-1814).

Vegetative
The Duvalia species are succulent, perennial plants with low, planar growth. The stems are clavate, cylindrical to spherical, in cross-section four-, five-or six-edged, and to about 10 inches long. They can range from green, gray to mottled reddish in color.

The stems of some species, such as the rounded Duvalia parviflora, are distinctive, and these species can be identified even when not in flower. However the stems are very variable, and most Duvalia species can only be distinguished from each other when the flower is seen.

The stems are superficially very similar to those of the related genus Piaranthus, and the two are often confused when not in flower. In cross-section, Duvalia stems are sometimes five or six sided (Piaranthus stems are always four-sided in cross-section). To accurately distinguish them however, it is necessary to examine the flowers.

Floral
The distinctive flowers are on long, bare stalks, which grow from the base of the stems.

Each flower has five thin, elongated petal-like lobes, radiating in a star-shape, from a central raised disk or annulus.

The colour of most species flowers is shades of reddish brown, except for those of the rare Duvalia parviflora which are cream-coloured. The hermaphroditic flowers measure 1–5 cm in diameter, and have five parts. The crown is yellow ocher, brown, red to dark purple. The five corolla lobes are flat or folded along the middle nerve.

Distribution
It occurs in southern Africa. The majority of the species are restricted to the western part of South Africa & Namibia, with the greatest number of species occurring in the Great Karoo region, on the edge of the winter rainfall area. Only one species, Duvalia polita extends further east, and as far north into tropical Africa as Malawi and Zambia.

Four species, occurring on the other side of the continent on the verges of the Red Sea, were formerly included in the genus Duvalia. However phylogenetic studies have shown them to be relatively unrelated to the rest of the genus, and more closely related to genus Ballyanthus Bruyns.

• # Duvalia anemoniflora (Deflers) R.A. Dyer & Lavranos - Arabia
 * Species

• # Duvalia angustiloba N.E.Br. - South Africa

• # Duvalia caespitosa (Masson) Haw. - South Africa

• # Duvalia corderoyi (Hook.f.) N.E.Br. - South Africa

• # Duvalia eilensis Lavranos - Somalia

• # Duvalia elegans (Masson) Haw. - Cape Province

• # Duvalia galgallensis Lavranos - Somalia

• # Duvalia gracilis Meve - Cape Province

• # Duvalia immaculata (C.A.Lückh.) M.B.Bayer ex L.C.Leach - South Africa

• # Duvalia maculata N.E.Br. - South Africa

• # Duvalia modesta N.E.Br. - South Africa

• # Duvalia parviflora N.E.Br. - Cape Province

• # Duvalia pillansii N.E.Br. - Cape Province

• # Duvalia polita N.E.Br. - South Africa

• # Duvalia pubescens N.E.Br. - Cape Province

• # Duvalia somalensis Lavranos - Somalia

• # Duvalia sulcata N.E.Br. - Arabia

• # Duvalia velutina Lavranos - Saudi Arabia

• # Duvalia vestita Meve - Cape Province

transferred to Mannia
 * formerly included
 * Duvalia rupestris now Mannia rupestris