Ranunculaceae (Buttercup Family)

British Isles, v.c. 15.

Above: Ficaria verna (= Ranunculus ficaria) subsp. bulbifera (= subsp. verna) or Lesser Celandine (Fig Buttercup). This species is found naturally across Europe, parts of Africa and Asia adjacent to Europe. It is found mainly in damp woodlands, but also in meadows, on hedgebanks and roadsides. It flowers early in Spring from around March to May.

The Ranunculaceae (Crowfoot family, Buttercup family) exhibits a phenomenal diversity of floral forms, from the familiar Buttercup, one section of the crowfoots (Ranunculus), to the showy Clematis, to the exotic looking Monk's-hood (Aconitum) and the peculiar Mousetail (Myosurus). The anunculaceae are annual or perennial herbs or climbing shrubs (e.g. Clematis). and consists of some 59 genera and about 2500 species.

Ficaria verna exhibits nyctinasty: the flowers open in the morning and close in the evening and also close in wet weather. This has been shown to protect the flowers against certain herbivores in this species. Wetting itself has been shown to have no negative impact on flower function.

Note that the outer parts of the petals are glossy with prominent specular highlights; here the epidermal cells have thin smooth walls and are anucleate cells (cells lacking a cell nucleus) that are filled with an oily solution of a yellow carotenoid. The flat surface of these cells creates a polished mirror effect. (Petals with conical or papillate epidermal cells tend to give rise to matte colors - they reflect diffuse light). Beneath this layer of epidermal cells is a layer of hypodermal cells that are also anucleate and are packed with white starch grains that reflect light. Thus, light passes twice through the yellow epidermal cells to intensify the color and the reflective starch later (which I suspect works by a diffraction mechanism) adds the glossy specular effects. Actually, a thin layer of air separates the epidermal and hypodermal layers which also reflects back light as does the waxy cuticle.

Specular highlights occur when the intensity of reflected light depends on both the angle of illumination and the angle of the viewer and are created by reflection from many microscopic mirror-like micro-facets. When more of these facets reflect light back to the eye at a certain angle, a highlight appears. These highlights tend to catch the eye, especially when the eye is moving and may serve to attract the attention of flying insects to affect pollination.

Note that the base of each petal is a dull matte. The backs of the petals are also a yellow matte, due to a yellow pigment in the plastids. At the base of each petal a tiny scale conceals a nectary which opens via a pore.

British Isles, v.c. 15. The leaves visible here belong to Wood Anemone.

Lesser Celandine is found in disturbed habitats and also in forests / woods and along the shores of rivers and lakes. The flower has 7 or more separate petals, 3 (to 5) sepals, 13 or more stamens (up to 60+) and a number of carpels in the center. (Young stamens may resemble young carpels). It occurs in the eastern, southeastern and northwestern USA where it is often invasive. Floral formula:

*K3-5 C8-11 A 15-31 G 9-10

Note that the ovaries are superior.

Each carpel forms a dry fruit, which does not split open, called an achene or nut; 15 to 30 or more achenes may be produced. The individual achenes may also be referred to as nutlets or fruitlets when 'fruit' is applied to the whole group of achenes. The seedling has one fan-shaped cotyledon. Several subspecies are known. The one above is subsp. bulbifera (verna). This tetraploid form is almost sterile (the nuts are mostly sterile) and reproduces mainly by the formation of axillary tubers that form in the leaf axils after flowering. There is no basal rosette of leaves in this form and characteristically the petals are not overlapping.

Below: the other subspecies common to the British Isles, subsp. fertilis has fertile nuts and the petals are more-or-less overlapping (again there is no basal rosette). The cordate (heart-shaped) leaves are characteristic of this species.

The high reflectivity and specular highlights can make it difficult to photograph Ficaria and Ranunculus. Some experimentation with exposure setting may be required as the flowers may easily glare or even white-out on digital cameras.

Buttercups or Sun-Eyes, Ranunculus spp., have similarly bright petals with the same mechanism of reflection discussed above in Ficaria. They also have petal-scales containing nectaries, one at the base of each petal.

Ranunculus bulbosus (Bulbous Buttercup)

Bulbous Buttercup prefers dry calcareous soils. A key feature is the bulbous swelling which is generally visible at the base of the stem as the rootstock forms a swollen corm-like storage organ.

British Isles, v.c. 15.

Above:diagnostic of this species are the reflexed sepals. These form an important part of the pollination mechanism. Buttercups span a spectrum from insect-pollination to rain-pollination. Ranunculus acris flowers nod in the rain, keeping them dry for insect pollination and the interiors of the flowers provide shelter for pollinators from the rain (though older flowers may self-pollinate if insect cross-pollination fails). Others rely on insect pollination and/or rain pollination.

In rain pollination, the cup-like flowers trap rain water. Only certain parts of the flower are wettable, such as the non-glossy bases of the petals. Water is taken up by the carpels by capillary action (adhesion and cohesion due to electrostatic forces) carrying the pollen to the receptive stigmas for self pollination. This only works if the cup does not overfill, for then the pollen would be lost. Buttercups have narrow gaps between the petal bases to allow excess water to slowly drain. Conversely, however, if this only works if water does not drain too quickly. These gaps are opposed by the sepals, so water collects in between the petals and sepals, further slowing water escape. In Ranunculus bulbosus the recurved sepals retain water better, aided by the hairs visible on the sepals facing the flower stalk. Excess water then slowly trickles down the flower stalk. In short, this forms a leak valve to regulate the amount of water in the petal cup.

In Ranunculus flammula (Lesser Spearwort) the stamens bend outwards and downwards when moistened, coming to lie down on the surface of trapped water to shed floating pollen

Above: Ranunculus bulbosus is visited by a variety of insects, including Thrips as seen here. Thrips possibly effect pollination (especially self-pollination) when the flower is dry.

Ranunculus acris (Meadow Buttercup)

British Isles, v.c. 37.

Another perennial species, with a short rootstock.The stems are erect, the petals have nectary scales at their bases and the sepals are hairy. As the name suggests this species is commonly found in meadows and grassland but also in coppiced woods.

British Isles, v.c. 37.

The leaves are pentagonal in outline but are cleft or clearly divided up into three segments (tripartite leaves) which are themselves deeply cut or toothed.

Ranunculus repens (Creeping Buttercup, Creeping Crowfoot)

British Isles, v.c. 37.

 R. repens is also a perennial and has a short rootstock which gives rise to a decumbent stem (may be more robust and erect in moist, shady places) which gives out flowering shoots and, later in the year, creeping and rooting runners. The leaves are stalked and ternate or bi-ternate with the middle leaflet (and sometimes also the laterals) stalked. The petal bases (claws) bear nectaries covered in nectary scales. It occurs on hedgebanks, along riversides and in meadows and on disturbed ground.

A meadow of buttercups, mostly R. acris with some R. repens. British Isles, v.c. 37.

The genus Ranunculus contains the aquatic Water-Crowfoots. These may exhibit pronounced heterophylly - the growth of different leaf forms on the same plant, with submerged leaves typically being highly divided into narrow segments (capillary leaves) and terrestrial leaves more blade-like. This can be seen in Ranunculus aquatilis (Common Water-crowfoot) in specimens that have floating leaves in addition to the usual submerged capillary leaves; the floating leaves being reniform (kidney-shaped) or orbicular (circular) and more-or-less divided into 3 lobes or parts.

Many plants possess hydathodes on their leaf margins, but these are well studied in Ranunculaceae. These typically consist of colorless, loosely-packed and thin-walled subepidermal cells forming a tissue called epithem. Tracheids in the vascular strand end blindly in the epithem into which xylem sap is excreted to escape to the outside via a water pore (typically a modified stoma). These function to allow transpiration to occur via positive root pressure, supplying mineral nutrients to the plant's parts even in the absence of appreciable transpiration. (Active pumping by the epithem is possibly also involved). Root pressure is particularly important in herbaceous plants (trees are too tall to utilize root pressure and must rely chiefly on evapotranspiration to create negative suction pressure in the xylem; see: water transport in plants).

Ranunculus fluitans (River Water Crowfoot) is found in clear flowing streams. The stems are rooted at their nodes, except for the upper five or six which trail freely in the water. The leaves are all submerged capillary leaves with a single (weakly developed) vascular strand supplying each roughly cylindrical segment. The tip of each segment is equipped with three hairs and three water pores (modified stomata complete with guard cells). These water pores belong to hydathodes and excrete sap to maintain a pressure gradient to drive xylem flow under water for mineral transport. In older leaves the guard cells are lost, resulting in large open pores in which the epithem secretes a gumming resin to block water flow across the epithem, so that the hydathodes are no longer functional.

Anemone nemorosa (Wood Anemone, Wind-Flower))

British Isles, v.c. 15.

When the Wood Anemone flower first opens, the stamens crowd over the stigmas but diverge away from the center later on so the stigmas can receive pollen - the flower is apparently protandrous (the male organs ripen first). A variety of insects (inc. beetles, flies, hoverflies, bees, thrips) will take pollen. It is often stated that the flower produces no nectar and that insects visit for the pollen, however, recent studies show that a small quantity of nectar is produced. There are no petals in Anemone, but the 6 (5 to 9) sepals are petal-like. The achenes are covered with downy hairs. the peduncle becomes hooked when bearing fruit, presumable to aid dispersal of the fruit by dropping. Anemone nemorosa occurs in woods and 'shrubby places' such as hedgebanks and is also found on heathland, moorland and rocky places such as scree and limestone pavements.

British Isles, v.c. 15.

Each inflorescence ends in a single flower borne on a long pedicel which emerges from an involucre of three stalked leaf-like bracts, each ternate (the blade divided into three main sections) with the separate segments pinnatifid (feather-like) or less deeply cut into more-or-less pointed lobes.One or two radical leaves emerge from the rootstock, from a separate point to the flowering stem or scape (a scape is a long internode forming the base of the peduncle or inflorescence stalk). These radical leaves are bi-ternate (the blade is divided into 3 main sections, each divided into 3 again) with pinnatifid segments. Thus, the main above-ground shoot is the inflorescence with its leafy bracts. The rootstock itself is a creeping rhizome only a few mm in diameter and brown-black in color. This plant is a rhizomatous perennial.

British Isles, v.c. 15.

Note that although Anemone has a whorl of petal-like sepals or tepals the stamens and carpels retain a primitive feature: they are in spiral whorls and variable in number. This is an ancestral trait of flowering plants: the flower evolves from a spiral of modified leaf-like appendages, one borne on each node, with the internodes shortening towards the shoot apex. These modified leaves which express different genes as they near the shoot apex, genes to turn them into sepals, petals, stamens or carpels. Eventually these spirals of floral organs or appendages become definite whorls with definite numbers in each whorl.

Anemone apennina (Blue Anemone, Blue Mountain Anemone, Apennine Anemone)

British Isles, v.c. 15.

Anemone apennina is also a rhizomatous perennial, but the rootstock is thick, olive-black and tuber-like. It is native to southern central Europe. It occurs, for example, on the Apennine mountains of the Italian Peninsulabut is also a garden favorite and garden escapes have naturalized in other parts of Europe. Solitary flowers are borne on pedicels, each pedicel emerging from an involucre of 3 leafy-bracts (each a ternate leaf with pinnatifid segments as can be seen above); 1 to 3 bi-ternate radical leaves (with pinnatifid segments) emerge from the same point on the rhizome as the scape. The carpels and achenes are smooth and hairless. The calyx consists of about 10 or 12 blue ligulate sepals (the specimen above has 16). The specimen above is certainly a garden escape.

Anemone coronaria (Poppy Anemone)

Anemone coronaria also has single flowers on each inflorescence with 3 to 5 bracts, with toothed or lobed margins towards the tip, forming the involucre. About 300 or more stamens occur in each flower, maturing from the outside in. Each flower has about 1000 carpels, each containing a single ovule. The stigma is the dry type and is elongated and covered with unicellular papillae. The achenes are covered in soft curled hairs.

This plant is native to the Mediterranean, but widely planted as an ornamental elsewhere. It occurs in red, purple-blue and white color morphs. It is perennial. There are about 150 species in the genus Anemone.

Nigella damascena (Love-in-a-mist, Devil-in-the-bush)

A popular garden plant, the specimen shown here is a garden escape. Note the highly divided bracts. Below: the characteristically large swollen fruit capsule.

Nigella damascena occurs in the Mediterranean and Near East

Ranunculaceae part 2 - Hellebore and Evolution of the Ranunculaceae

Article updated: 28 Dec 2020, 5 Mar 2023