Diascia

Diascia is a genus of usually low-growing, annual and perennial herbs in the Scrophulariaceae or snapdragon family.

The generic name, Diascia, is derived from the Greek words dis meaning twice or double and askos meaning a wine-skin or bag, referring surprisingly not to the spurs, but to the pair of translucent sacs or windows found in the upper part of the corolla of the original type specimen, Diascia bergiana. The plants are commonly known as twinspurs and in Afrikaans as pensies (little stomachs), a corruption of the English word, pansies.

The leaves are opposite or in basal rosettes, while some species have alternate upper leaves, also sometimes differently shaped in the lower ones. Most leaves have petioles, the leaf-shape variable from linear to obovate or nearly circular. Leaf margins are toothed or dissected, rarely entire, the blades usually hairless.

The flowers grow solitary in stem-tip racemes or fascicles. The calyx is five-lobed, tending to enlarge during the fruiting stage.

The corolla is usually shortly tubular and two-lipped. The upper lip mostly has two or four rounded lobes, while there is usually one large lobe on the lower one, sometimes slightly divided into three. Flower colour is often pink or purple, while yellow or orange flowers are less common. The corolla centre is often darker and there are sometimes yellow windows in the corolla.

Inside the lower lip the cup in several species is usually extended into two downward pointing spurs, pouches or slight hollows where trichomes (glandular hairs or papillae) are present that secrete oil, not nectar. This special oil is collected by bees of the Rediviva genus, often adapted or coevolved with a particular species, the long, hairy forelegs fitting the spurs of their particular flower species. Translucent (yellow) windows, visible on both inside and outside, may be present in the corolla tissue near the pouches or spurs.

There are usually four stamens in two unequal pairs in each flower, arising in the corolla mouth and twisted around each other. The ovoid ovary has two locules containing many ovules. The style is cylindrical, the stigma small. The fruit is obliquely ovoid, globular or elongated. The numerous brown seeds are usually curved and ribbed or sometimes pitted.

There are about 70 species of Diascia, all occurring in southern Africa. The annuals tend to grow in the winter rainfall west, the perennials in the summer rainfall east. There are many, floriferous cultivars in horticultural use, mostly perennials.

The plant in picture is D. whiteheadii (Leistner, (Ed.), 2000; Manning, 2007; Andrew, 2017; Wikipedia).