Fringed twinevine (Funastrum cynanchoides) was previously included in the Milkweed Family but is now considered a member of the Dogbane Family (Apocynaceae). Funastrum cynanchoides currently has a confused taxonomy with some researchers believing it should be separated into two subspecies while others feel dividing it into two distinct species is appropriate. Whether there are two subspecies or two species, they all hybridize. I will simply use F cynanchoides, but if pressed believe this plant belongs to the subspecies hartwegii.
A native perennial, fringed twinevine grows at the edge of dry, rocky sandy desert washes (arroyos) in the Eastern Mojave Desert and the Sonoran Desert.
The long, narrow twisting stems grow over other shrubs and exude a milky sap when injured. The opposite, hairless leaves are variable in shape but usually resemble a linear arrowhead. The foliage has a disagreeable odor, sometimes described like burning rubber.
The inflorescence is composed of pink to purplish flowers arranged in a head. There are 5 triangular sepals. The 5 petals are fringed with white hairs. The flower centers have 5 white appendages separate from the base of the corolla (petals collectively), 5 light brown anthers and a greenish filament column topped by a two-lobed pistil.
The fruits resemble a milkweed pod being tear-drop shaped follicles 3 to 4 inches long. When dry the fruits of fringed twinevine split open to reveal brown seeds with long, silky, white hairs. The seeds are wind borne. The young fruits are edible.
The genus name comes from the Latin “funis” (rope or cord) and “astrum” (incomplete resemblance) and refer to the long, narrow stems. The species name probably also alludes to the stems – the Greek word “kyon” means dog and “anchein” means to strangle. The German botanist Karl Theodor Hartweg (1812 – 1871) is honored by the subspecies (or species). Hartweg collected plants and seeds for the London Horticultural Society.
Other colloquial names for F cynanchoides are climbing milkweed and narrowleaf climbing milkweed. A synonym is Sarcostemma cynanchoides.
In April I photographed these fringed twinevine specimens in an arroyo behind Casa Paloma 2 in Green Valley AZ. Notice in one photograph the flower has six sepals, petals, appendages and anthers instead of five.