A remarkable little plant, the systematic position of which is very doubtful. It was originally placed in Tillæa by Kirk, and no doubt there is considerable outward similarity with that genus, although it differs fundamentally in the gamopetalous corolla, the 4-lobed ovary, and the simple imbedded style. Prof. Oliver, no doubt influenced by the 4-lobed ovary, transferred it to the Boraginaceæ, although he points out ("Icones Plantarum," t. 2250) that it departs from the characters of the order in the opposite leaves connate at the base, and in the albuminous seeds. Dr. Hans Hallier, in an interesting paper printed in the "Berichten der Deutschen Botanischen Gesellschaft" for 1902, suggests that it should be considered an anomalous member of the Scrophularineæ, and that its nearest ally is the section Pygmea of Veronica. A study of the early development of the corolla would probably either prove or disprove this view.
Order LII. CONVOLVULACEÆ.
Herbs or shrubs, frequently twining, often with milky juice. Leaves alternate, exstipulate, wanting in Guscuta. Flowers regular, usually hermaphrodite, axillary, solitary or cymose, often large and showy. Calyx inferior, persistent, usually of 5 distinct imbricated sepals. Corolla gamopetalous, hypogynous, campanulate or funnel-shaped or rotate, limb shortly or deeply 5-lobed or almost entire, often plaited and contorted in bud. Stamens 5, inserted on the tube of the corolla and alternate with its lobes; anthers oblong, opening lengthwise. Ovary superior, usually surrounded by an annular disc, 2–4-celled, rarely 1-celled, sometiines divided into 2–4 distinct carpels; style single or 2; stigma capitate or 2-lobed or branched; ovules usually 2 in each cell or carpel, erect, anatropous. Fruit a 1–4-celled capsule, 2–4-valved or bursting transversely or irregularly, rarely succulent and indehiscent. Seeds erect; albumen scanty or wanting; embryo curved, cotyledons broad, much folded and crumpled (in Cuscuta the embryo is spiral and undivided).
A moderately large order, widely spread over the whole world, but most plentiful in warm or tropical climates. Genera 32; species about 800. As a rule, the roots abound in a milky and acrid juice, which is often strongly purgative and used in medicine, as jalap and scammony. In some species the roots are inert and edible, as the common sweet potato, so largely cultivated in all warm countries. Many species of Ipomœa and allied genera are grown for the sake of their large and showy flowers. All the New Zealand genera have a wide range.
| * Leafy plants, twining or prostrate. | |
| † Corolla plaited. Style single. | |
| Ovary 2–4-celled. Stigma capitate, or lobes globose | 1. Ipomœa. |
| Ovary imperfectly 2-celled. Stigmas 2, oblong, flat. Bracts large, enclosing the calyx | 2. Calystegia. |
| Ovary 1-celled. Stigmas 2, linear, flat. Bracts small or wanting | 3. Convolvulus. |
| †† Corolla rotate. Styles 2. | |
| Ovary of 2 separate carpels | 4. Dichondra. |
| ** Leafless twining parasites. | |
| Corolla small, campanulate | 5. Cuscuta. |
