1911 Encyclopædia Britannica/Ranunculaceae

^{From Vines's Students’ Text Book of Botany, by permission of Swan, Sonnenschein & Co.}
Fig. 1. — Gynoecium of Ranunculus: x, receptacle with the points of insertion of the stamens, which have been removed.

RANUNCULACEAE, in botany, a natural order of Dicotyledons belonging to the subclass Polypetalae, and containing 27 genera with about 500 species, which are distributed through temperate and cold regions but occur more especially beyond the tropics in the northern hemisphere. It is well represented in Britain, where 11 genera are native. The plants are mostly herbs, rarely shrubby, as in Clematis, which climbs by means of the leaf-stalks, with alternate leaves, opposite in Clematis, generally without stipules, and flowers which show considerable variation in the number and development of parts but are characterized by free hypogynous sepals and petals, numerous free stamens, usually many free one-celled carpels (fig. 2) and small seeds containing a minute straight embryo embedded in a copious endorsperrn. The parts of the flower are generally arranged spirally on a convex receptacle. The fruit is one-seeded, an achene (fig. 3), or a many-seeded follicle (fig. 4), rarely, as in Actaea, a berry.

The order falls into several well-defined tribes which are distinguished by characters of the flower and fruit; all are represented among British native or commonly grown garden plants.

From Strasburger's Lehrbush der Botanik, by permission of Gustav Fischer. Fig. 2. — Ranunculus arvensis. Carpel in longitudinal section. (After Baillon, enlarged.)

Fig. 3. — Single follicle showing dehiscence by the ventral suture.

Fig. 4. — Fruit of Columbine (Aquilegia) formed of five follicles.

Tribe I. Paeonieae, peony group, are mostly herbs with deeply cut leaves and large solitary showy flowers in which the parts are spirally arranged, the sepals, generally five in number, passing gradually into the large coloured petals. The indefinite stamens are succeeded by 2–5 free carpels which bear a double row of ovules along the ventral suture. Honey is secreted by a ring-like swelling round the base of the carpels, which become fleshy or leathery in the fruit and dehisce along the ventral suture. There are only three genera, the largest of which, Paeonia, occurs in Europe, temperate Asia and western North America. P. officinalis is the common peony.

Tribe II. Helleboreae are almost exclusively north temperate or subarctic; there are 15 genera, several of which are represented in the British flora. The plants are herbs, either annual, e.g. Nigella (love-in-a-mist), or perennial by means of a rhizome, as in Aconitum or Eranthis (winter aconite). The leaves are simple, as in Caltha, but more often palmately divided as in hellebore (fig. 6), aconite (fig. 5) and larkspur.

Fig. 5. — Five-partite leaf of Aconite.

Fig. 6. — Pedate leaf of Stinking Hellebore (Helleborus foetidus). It is a palmately-partite leaf, in which the lateral lobes are deeply divided. When the leaf hangs down it resembles the foot of a bird, and hence the name.

The flowers are solitary (Eranthis) or in cymes or racemes, and are generally regular as in Caltha (king-cup, marsh marigold), Trollius (globe-flower), Helleborus, Aquilegia (columbine); sometimes medianly zygomorphic as in Aconitum (monkshood, aconite) and Delphinium (larkspur). The-carpels, generally 3 to 5 in number, form in the fruit a many-seeded follicle, except in Actaea (bane berry), where the single carpel develops to form a many-seeded berry, and in Nigella, where the five carpels unite to form a five-chambered ovary. There is considerable variety in the form of the floral envelopes and the arrangement of the parts. The outer series, or sepals, generally five in number, is generally white or bright-coloured, serving as an attraction for insects, especially bees, as well as a protection for the rest of the flower. Thus in Caltha and Trollius the sepals form a brilliant golden-yellow cup or globe, and in Eranthis a pale yellow star which contrasts with the green involucre of bracts immediately below it; in Nigella they are blue or yellow, and also coloured in Aquilegia. In Hellebore the greenish sepals persist till the fruit is ripe. Aconitum and Delphinium differ in the irregular development of the sepals, the posterior sepal being distinguished from the remaining four by its helmet-shape (Aconitum) or spur (Delphinium). In Caltha there are no petals, but in the other genera there are honey-secreting and storing structures varying in number and in form in the different genera.

Fig. 7. — Helleborus niger. 1, vertical section of flower; 2, nectary, side and front view (nat. size).

In Trollius they are long and narrow with a honey-secreting pit at the base, in Nigella and Helleborus (fig. 7) they form short stalked pitchers, in Aquilegia they are large and coloured with a showy petal-like upper portion and a long basal spur in the tip of which is the nectary. In Delphinium they are also spurred, and in Acomtum form a spur-like sac on a long stalk (fig. 8). The parts of the flower are generally arranged in a spiral (acyclic), but are sometimes hemicyclic, the perianth forming a whorl as in winter aconite; rarely is the flower cyclic, as in Aquilegia (fig. 9) where the parts throughout are arranged in alternating whorls. In Caltha, where there are no petals, honey is secreted by two shallow depressions on the side of each carpel.

Fig. 8. — Part of the flower of Aconite (Aconitum Napellus), showing two irregular horn-like petals p, supported on grooved stalks o. These serve as nectarines. s, the whorl of stamens inserted on the thalamus, and surrounding the pistil.

Fig. 9. — Floral diagram of Columbine (Aquilegia) showing regular cyclic arrangement.

Tribe III. Anemoneae, with 8 genera, are chiefly north temperate, arctic and alpine plants, but also pass beyond the tropics to the southern hemisphere. They differ from the two preceding tribes in the numerous carpels, each with only one ovule, forming a fruit of numerous achenes. They are annual or perennial herbs, erect as in Anemone, Thalictrum (meadow-rue) and many buttercups, or creeping as in Ranunculus repens; the section Batrachium of the genus Ranunculus (q.v.) contains aquatic plants with submerged or floating stems and leaves. The flowers are solitary, as in Anemone Pulsatilla (Pasque flower) and the wood anemone, or cymose as in species of Ranunculus, or in racemes or panicles as in Thalictrum. The parts are spirally arranged throughout as in Myosurus (mouse-tail), where the very numerous carpels are borne on a much elongated receptacle, or Adonis (pheasant's eye), or the perianth is whorled as in Anemone and Ranunculus. In Anemone there is a whorl of foliage leaves below the flower, as in Eranthis. In Anemone and Thalictrum there is only one series of perianth leaves, which are petaloid and attractive in Anemone where honey is secreted by modified stamens, as in A. Pulsatilla, or, as in A. nemorosa (Wood anemone), there is no honey and the flower is visited by insects for the sake of the pollen; in Thalictrum the perianth is greenish or slightly coloured and the flower is wind-pollinated (T. minus) or visited for its pollen. In Ranunculus and Adonis a calyx of green protective sepals is succeeded by a corolla of showy petals; in Ranunculus (fig. 10) there is a basal honey-secreting gland which is absent in Adonis. In Anemone the achenes bear the persistent naked or bearded style which aids in dissemination; the same purpose is served by the prickles on the achenes of Ranunculus arvensis.

Fig. 10. — Petal of Crowfoot (Ranunculus), bearing at the base a honey gland protected by a scale, s.

Tribe IV. Clematideae comprise the genus Clematis (q.v.), characterized by its shrubby, often climbing habit, opposite leaves and the valvate, not imbricate as in the other tribes, aestivation of the sepals. The usually four sepals are whorled and petaloid, the numerous stamens and carpels are spirally arranged; the flowers are visited by insects for the sake of the abundant pollen. The fruit consists of numerous achenes which are generally prolonged into the long the feathery style, whence the popular name of the British species, old man's beard (Clematis vitalba). The genus, which contains about 170 species, has a wide distribution, but is rarer in the tropics than in temperate regions.

Special articles will be found on the more important genera of Ranunculaceae, e.g. Aconitum, Adonis, Anemone, Baneberry (Actaea), Clematis, Columbine, Hellebore, Ranunculus.