Such are Papilionaceous flowers, Violaceae, many Labiatae, Scrophulariaceae and others.
In the low brushwood scattered over portions of the dreary plains of the Kandahar table-lands, we find leguminous thorny plants of the papilionaceous sub-order, such as camel-thorn (Hedysarum Alhagi), Astragalus in several varieties, spiny rest-harrow (Ononis spinosa), the fibrous roots of which often serve as a tooth-brush; plants of the sub-order Mimosae, as the sensitive mimosa; a plant of the rue family, called by the natives lipdtd; the common wormwood; also certain orchids, and several species of Salsola.
When the different members of each whorl are like in size and shape, the flower is said to be regular; while differences in the size and shape of the parts of a whorl make the flower irregular, as in the papilionaceous flower, represented in fig.
- Flower of Pea (Pisum sativum), showing a papilionaceous corolla, with one petal superior (st) called the standard (vexillum), two inferior (car) called the keel (carina), and two lateral (a) called wings (alae).
- Diagram of a papilionaceous flower, showing vexillary aestivation.
In some cases, as in papilionaceous flowers, the stamens cohere, having been originally separate, but in most cases each bundle is produced by the branching of a single stamen.
In his book on the fertilization of flowers, Hermann Muller distinguishes four types of papilionaceous flowers according to the way in which the pollen is applied to the bee: (I) Those in which the stamens and stigma return within the carina and thus admit of repeated visits, such are the clovers, Melilotus and laburnum.