Ranunculaceae
Buttercup Family
Order: Ranunculales
Phylogenetic Position: Early-diverging eudicots
Family Overview
The Ranunculaceae, commonly known as the buttercup family, is a diverse family of flowering plants that includes approximately 2,000 species in about 50 genera. This family is distributed worldwide but is most diverse in temperate and cold regions of the Northern Hemisphere. The Ranunculaceae is an ancient family that represents one of the early-diverging lineages of eudicots in the angiosperm phylogeny.
Members of this family are primarily herbaceous perennials, with some annuals and a few woody climbers (like Clematis). They are known for their often showy flowers with numerous stamens and carpels, and many species are cultivated as ornamentals. Some members contain toxic alkaloids and have been used in traditional medicine, though they can be poisonous if misused.
The Ranunculaceae is characterized by its basal position in eudicot evolution, showing some primitive floral features while also exhibiting specialized adaptations in various genera. This family is of significant ecological importance, with many species serving as early spring wildflowers in temperate ecosystems and providing important nectar sources for pollinators.
Botanical Characteristics
Growth Form
Primarily herbaceous perennials or annuals, with a few woody climbers (Clematis). Plants often have fibrous roots, rhizomes, or tuberous roots. Many species are low-growing, while others can reach up to 2 meters in height.
Leaves
Leaves are typically alternate, sometimes basal, and often compound or deeply divided with palmate or pinnate venation. Leaf shapes vary widely from simple to highly dissected. Petioles are often present and may be sheathing at the base. Stipules are usually absent.
Stems
Stems are usually herbaceous, sometimes hollow, and may contain colored sap in some genera. In climbing species like Clematis, stems can be woody and use leaf petioles as tendrils for climbing.
Flowers
Flowers are usually radially symmetric (actinomorphic), bisexual, and hypogynous (with superior ovaries). They typically have 5 sepals (sometimes 3-6), which are often petal-like and colorful. True petals may be present or modified into nectaries, or sometimes absent. Stamens are numerous (often 10 or more) and spirally arranged. Carpels are also usually numerous and separate (apocarpous).
Fruits
Fruits are typically either achenes (dry, single-seeded fruits) or follicles (dry fruits that split along one side to release seeds). Some genera produce berries. Seeds often have small embryos and abundant endosperm.
Specialized Features
Many members contain toxic alkaloids or glycosides as chemical defenses. Some species have specialized nectar-producing structures modified from petals. The family shows diverse pollination strategies, from generalist insect pollination to specialized mechanisms. Some species have adaptations for wind dispersal of seeds, with features like feathery styles (as in Clematis).
Field Identification
Primary Features
- Numerous stamens and carpels: The presence of many stamens and separate carpels in a spiral arrangement is a key feature.
- Divided leaves: Many species have compound or deeply divided leaves, often with palmate or pinnate patterns.
- Colorful sepals: The showy parts of the flowers are often sepals rather than petals, which may be reduced or modified.
- Lack of stipules: Unlike some similar families, Ranunculaceae typically lacks stipules at the leaf bases.
- Hypogynous flowers: Flower parts attached below the ovary (superior ovary).
Secondary Features
- Habitat preference: Many species prefer moist habitats or flower in early spring.
- Basal leaf arrangement: Several genera have primarily basal leaves.
- Nectar spurs: Some genera (like Aquilegia) have distinctive nectar spurs.
- Fruit type: The presence of either achenes or follicles can help confirm identification.
- Acrid taste: Many species have an acrid, bitter taste if a tiny piece is sampled (though tasting is not recommended due to toxicity).
Seasonal Identification Tips
Spring: Many species flower in early spring before tree canopies leaf out. Look for colorful flowers with numerous stamens and often deeply divided leaves.
Summer: Fruiting structures with multiple achenes or follicles are distinctive. Some species continue flowering into summer.
Fall/Winter: Persistent fruit heads may remain visible in some species. Evergreen basal leaves may be present in some genera.
Potential Confusion Points
- Rosaceae: Also has numerous stamens but typically has stipules and often has united carpels or a hypanthium.
- Papaveraceae: Has numerous stamens but typically has milky or colored sap and only 2-3 sepals that fall off as the flower opens.
- Berberidaceae: Related family in the same order but typically has parts in multiples of 3 or 6 rather than 5.
Notable Examples
Ranunculus (Buttercups)
The largest genus in the family, with about 600 species. Known for their glossy yellow flowers with 5 petals and numerous stamens. Many species have deeply divided leaves. Some are aquatic. Common examples include the common buttercup (R. acris) and creeping buttercup (R. repens).
Ecological/Economic Importance: Some species are agricultural weeds. Many contain the glycoside ranunculin, which breaks down to the irritant protoanemonin when the plant is crushed, causing skin irritation and making them unpalatable to livestock.
Clematis (Virgin's Bower)
Woody climbing vines with opposite, usually compound leaves. Flowers typically have 4 showy sepals and no true petals. The fruits develop long, feathery styles that aid in wind dispersal. Popular garden plants with many cultivars.
Ecological/Economic Importance: Valuable ornamental plants. In the wild, they provide habitat for birds and insects. The feathery seed heads are important for seed dispersal mechanisms.
Anemone (Windflowers)
Perennial herbs with basal leaves and solitary flowers on long stalks. Flowers typically have 5-10 petal-like sepals and no true petals. Fruits are achenes, sometimes with woolly coverings.
Ecological/Economic Importance: Important early spring wildflowers in many ecosystems. Some species are cultivated as ornamentals. Some have been used in traditional medicine.
Aquilegia (Columbines)
Perennial herbs with compound leaves. Distinctive flowers have 5 sepals, 5 petals with backward-projecting spurs that contain nectar, and numerous stamens. The name "columbine" comes from the Latin for "dove," as the spurs resemble a circle of doves.
Ecological/Economic Importance: Important nectar sources for hummingbirds and long-tongued insects. Many species and hybrids are cultivated as ornamentals.
Delphinium (Larkspurs)
Annual or perennial herbs with palmate leaves. Flowers are irregular with 5 sepals, the upper one extended into a spur, and 4 petals. Colors are typically blue, purple, or white.
Ecological/Economic Importance: Many species are cultivated as ornamentals. Some contain toxic alkaloids that can be harmful to livestock. Some species are important in their native ecosystems as pollinator plants.
Helleborus (Hellebores)
Perennial herbs with leathery, divided leaves. Flowers have 5 petal-like sepals that persist long after flowering, and modified petals as nectaries. Many species flower in winter or early spring.
Ecological/Economic Importance: Valued as garden plants, especially for winter interest. Contains cardiac glycosides and has been used in traditional medicine but is toxic if misused.
Phylogenetic Position and Evolution
The Ranunculaceae is positioned within the order Ranunculales, which is one of the earliest-diverging lineages of eudicots in the angiosperm phylogeny. This basal position makes the family particularly interesting from an evolutionary perspective, as it retains some ancestral characteristics while also showing specialized adaptations.
Evolutionary Significance
- Primitive floral features: The numerous spirally arranged stamens and carpels represent an ancestral condition in flowering plants.
- Diverse perianth evolution: The family shows interesting patterns in the evolution of sepals and petals, with some genera having both clearly differentiated, while others have modified or reduced petals.
- Chemical evolution: The family has evolved diverse secondary compounds, particularly alkaloids and glycosides, as defensive adaptations.
- Pollination syndromes: Various specialized pollination mechanisms have evolved within the family, from generalist insect pollination to specialized adaptations for birds or specific insect groups.
Related Families
Other families in the Ranunculales order include:
- Berberidaceae (Barberry family)
- Papaveraceae (Poppy family)
- Menispermaceae (Moonseed family)
- Lardizabalaceae (Lardizabala family)
These families share some characteristics with Ranunculaceae but have diverged in various ways, such as the development of colored latex in Papaveraceae or the woody habit and different alkaloid profiles in Berberidaceae.
References and Further Reading
APG IV. (2016). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society, 181(1), 1-20.
Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 14, July 2017. http://www.mobot.org/MOBOT/research/APweb/
Tamura, M. (1993). Ranunculaceae. In K. Kubitzki, J. G. Rohwer, & V. Bittrich (Eds.), The Families and Genera of Vascular Plants (Vol. 2, pp. 563-583). Springer-Verlag.
Wang, W., Lu, A. M., Ren, Y., Endress, M. E., & Chen, Z. D. (2009). Phylogeny and classification of Ranunculales: Evidence from four molecular loci and morphological data. Perspectives in Plant Ecology, Evolution and Systematics, 11(2), 81-110.