6. Clematideæ, Clematis Group. This differs from all the others in the valvate æstivation of the calyx and its opposite leaves. There are 4 (-several) petaloid sepals; petals are absent, or linear (Atragene). Ovule 1, pendulous. Achenes, often with prolonged, feathery style. The majority of the genera are shrubs, and climb by their sensitive, twining leaf-stalks.—Clematis; Atragene.
Pollination. The flowers are conspicuous either by coloured petals (honey-leaves) (Ranunculus, Pæonia) or coloured sepals (Helleborus, Anemone, Caltha, etc.), or by both (Aquilegia, Delphinium), or by the coloured stamens (Thalictrum). Some have no honey (Clematis, Anemone, Thalictrum), and are generally visited by insects for the sake of their pollen. Others have nectaries on the corolla (Ranunculus, Trollius, Helleborus, Nigella, Aconitum, etc.), more rarely on the stamens (Pulsatilla, Clematis-species), or the carpels (Caltha), or the calyx (certain species of Pæonia). The honey is readily accessible in the flat, open flowers, and these flowers also may easily pollinate themselves. There is marked protandry where the honey lies deeply hidden, as in Aquilegia, Delphinium, and Aconitum. Helleborus and some Ranunculus-species are protogynous.
About 680 species; especially in northern temperate climates, and extending to the Polar and Alpine regions. Only the Clematideæ are tropical.
The order has an abundance of acrid, vesicant properties (R. acer, sceleratus, etc.), and poisonous alkaloids (Helleborus niger is poisonous). Officinal: Aconitum napellus (aconitine; leaves and tuberous roots); the rhizome of Hydrastis canadensis from N. Am. (the alkaloid hydrastine). The order, however, is best known for its ornamental plants; almost all the genera have species which are cultivated for their beauty. Sweet-scented flowers are absent.
Order 2. Nymphæaceæ (Water Lilies). Water Plants; generally with large, floating leaves, and large solitary flowers; sepals 3–5, petals 3–∞, stamens 6–∞, carpels 3–∞. The flower is hypogynous, but in the Nymphæeæ different degrees of epigyny are found, and from this fact, as well as from the carpels being united into one pistil, the family forms a lateral offshoot from the Ranunculaceæ, with much greater modification. The seed often has an aril, and, in the majority, a farinaceous nutritive tissue, partly endosperm, partly perisperm (Fig. [383] C). The embryo has 2 thick cotyledons and a small hypocotyl; the plumule is well developed, with 2–4 leaves.
1. Cabombeæ. 3–4 species (Tropical S. Am.), resembling the Water Ranunculus, with two kinds of leaves, the submerged being dissected and the aerial peltate. The flowers are eucyclic, trimerous, with 2–3 free, epigynous carpels. The ovules are situated on the central line of the carpel—an almost unique circumstance. Endosperm and perisperm. Cabomba; Brasenia.
2. Nelumboneæ. The leaves are peltate, raised on long stalks high above the water. Large, hypogynous flowers (Fig. [382]); sepals 4–5; petals numerous; stamens numerous; carpels several, distinct. The receptacle is very remarkable, being raised above the stamens, and developed into an inverted conical body on the apex of which the nut-like fruits are embedded in pits. Endosperm is wanting, but the embryo is large and has well developed cotyledons.—Nelumbo, 2 species. N. lutea (N. Am.); N. speciosa (E. Ind.) was sacred amongst the ancient Hindoos and Egyptians, (the Lotus flower); its seeds are used as food.
3. Nymphæeæ, Water Lily Group. The carpels are united into one, many-locular ovary, whose numerous ovules are situated on the surface of the partition walls (as in the Poppies); the stigma is sessile and radiating, the number of rays corresponding to the number of carpels (Fig. [383]). The fruit is a spongy berry with many seeds, which have a large perisperm in addition to the endosperm (Fig. [383] C).
Fig. 382.—Nelumbo nucifera: vertical section through the receptacle.