Order 8. Trigoniaceæ. Shrubs; Trop. Am.—30 species.
Order 9. Tremandraceæ. Polygalaceæ with regular flowers.—27 species. Australia.
Fig. 475.—Diagram of Polygala: d a gland in the posterior side of the flower; α and β the two caducous bracteoles.
Order 10. Polygalaceæ. Herbs or shrubs (some tropical species are lianes) with scattered (rarely opposite), simple and most frequently quite entire leaves, without stipules. The flowers are usually borne in terminal spikes or racemes, and are strongly zygomorphic (the plane of symmetry being median); they have 5 free sepals, the 2 lateral ones of which (4 and 5 in Figs. [475], [476]) are very large, petaloid, and frequently project on each side like the “wings” of a Pea-flower; petals 5, of which the two lateral ones are wanting or rudimentary (dotted on Fig. [475]), and the anterior “the keel” (Fig. [476] c) is large, hollow and boat-shaped, and frequently with a lobed or fimbriated edge (Fig. [476] A and B, c); stamens 8, the two median ones being absent, all united into a tube split along the back, which is also slightly united to the keel (the anthers, often 2 locular, open by pores, Fig. [476] B, st); the 2 median carpels form a bilocular ovary. 1 pendulous ovule in each loculus (Figs. [476] C, [475]); capsule compressed with loculicidal dehiscence, rarely a nut. Polygala (Milk-wort).
470 species; distributed over the whole globe (none Arctic). Officinal: the root of P. senega, from N. Am. Some are used as ornamental plants.
Pollination. The flowers of Polygala are pollinated by insects (chiefly bees). The fimbriated processes of the anterior petal support the insect when it alights. The anthers lie on each side of the stigma in the pouch of the anterior petal; the apex of the style is spoon-shaped, and immediately behind it is a viscid stigmatic lobe. In reaching the honey the proboscis of the insect must come in contact with the pollen and the viscid stigma, by which it is rendered sticky; this ensures the pollen adhering to the proboscis and so being carried to other flowers.
Fig. 476.—Polygala amara. Parts of the flower (mag.) A Flower from side, 1-5 sepals: c keel; B flower from above spread out: st the 8 stamens; c fimbriated edge of “keel”; C ovary with style and stigma.