B. Tetracyclicæ.
a. Tetracyclicæ with hypogynous flowers.
Family 29. Tubifloræ.
The flower is regular, ☿, and hypogynous. The gamopetalous type is present in this family with great uniformity, without suppression or splitting; S5, P5, A5, G2 (3–5). The stamens are all fertile, alternating with the lobes of the corolla. Gynœceum with 2, more seldom 3–5 syncarpous carpels. Style nearly always simple; 2 dorsal stigmas. In each carpel 2–∞ ovules. At the base of the ovary is found a yellowish ring-like nectary (Fig. [552] C), sometimes 5-sinuate or 5-partite.—The leaves are nearly always scattered; stipules are absent.—The Solanaceæ, which formerly were classed here, are so closely allied to the Personatæ, that it would be unnatural not to place them first in this family; and the Boraginaceæ (which were also placed in the Tubifloræ) appear to be best united, with the Labiatæ and others, into one family Nuculiferæ.
Order 1. Polemoniaceæ. The flowers are regular; S5, P5, A5, G3. The calyx and corolla have united leaves, the petals twisted to the right in æstivation (all the left edges being covered). The ovary is 3-locular with 2–∞ ovules in each loculus; the style is trifid at the apex; the fruit is a 3-valved capsule. Embryo straight; endosperm fleshy. The inflorescences are dichasia passing over into unipared helicoid cymes (the shoot of the lower bracteole being the more strongly developed).—Herbs without latex. 150 species; especially Western N. Am.—Phlox (salver-shaped corolla; entire, opposite leaves), Polemonium (campanulate or almost rotate corolla; scattered, pinnate leaves), Leptosiphon, Gilia, Collomia, Cobæa (climbing, like the Vetches, by tendrils at the ends of the leaves), etc. They are frequently ornamental plants.
Order 2. Hydrophyllaceæ. This order approaches very closely to the Boraginaceæ. Herbs with pinnate or palmate leaves; S5, P5, A5, G2. The lobes of the corolla are imbricate in æstivation. Generally 2 median carpels. The ovary is most frequently unilocular, and the seeds are situated on 2 parietal placentæ; capsule 2-valved; embryo straight; endosperm fleshy. In the corolla-tube, opposite the corolla-lobes, there are frequently appendages of various forms, which resemble those of Cuscuta. The inflorescences correspond exactly with those of the Boraginaceæ, being unipared scorpioid cymes, which, prior to opening, are tightly rolled up.—130 species, especially in N. Am. (California, etc.). Many annual species of Phacelia, Nemophila, Whitlavia, Eutoca, Cosmanthus, etc., are cultivated in gardens as ornamental plants. Hydrolea (has a bilocular ovary, and two free styles).
Order 3. Convolvulaceæ (Bindweeds). The flower is regular, hypogynous, with 5 almost free sepals (quincuncial æstivation), P5, A5, G2 (rarely 3–5). The corolla is very characteristic; it is (with various forms) almost entire, or slightly 5-lobed, and folded longitudinally in the bud in such a way that 5 projecting, flat portions, tapering towards the top and frequently differing in colour and hairiness from the rest, are visible externally and applied close together, while the remainder of the corolla is folded inwards (Fig. [552] A); and hence the whole corolla is strongly twisted to the right in the bud. The gynœceum most frequently has a bilocular ovary; in each loculus there are only 2 (erect) anatropous ovules on the placenta, which is not especially thickened (Fig. [552] D, E); each loculus is sometimes divided into two by a false septum (a relationship with the Boraginaceæ, etc.); style simple with most frequently a bilobed stigma, or a bipartite style. The fruit is nearly spherical, most frequently a capsule. The seeds are erect, and have a large hilum at the base. The embryo is curved, with leaf-like, thin, bilobed, most frequently folded cotyledons; endosperm absent or mucilaginous.
1. Convolvuleæ, Bindweed Group. The majority are twining (to the left) herbs, with latex. The leaves are scattered, without stipules, often long stalked, and nearly always with cordate base; some are palmately lobed. The flowers are most frequently solitary in the leaf-axils, large, quickly withering.—Convolvulus (Fig. [552]), Calystegia (unilocular ovary, 2 large bracteoles), Ipomœa, Batatas, Evolvulus (with a doubly bifid style), Calonyction, Pharbitis, etc.
Fig. 552.—Convolvulus scammonia.