The combination of bright-yellow, glossy-petalled flowers and fleshy, heart-shaped leaves sets lesser celandines apart from all other early-spring, herbaceous plants of seasonally-wet habitats in western and central Europe. The vivid petal colouration is a consequence of chemistry and anatomy; pigment-rich epidermal cells overlay cells rich in white starch grains.
The name Ficaria ('little figs') was first used for the lesser celandine by the early-sixteenth-century German botanist and theologian Otto Brunfels. Brunfels's Herbarum vivae eicones (1530-1536) has the twin distinctions of being one of the earliest botanical books to contain naturalistic illustrations and to be banned by the Vatican as heretical. Brunfels's 'little figs' are overwintering tubers at the plant's base. Under the Doctorine of Signatures these tubers were thought to resemble haemorrhoids, hence another of the plant's common names, pilewort.
One of its chemical defence mechanisms is based on a glucoside called ranunculin. When the fresh plant is damaged, enzymes break ranunculin down into glucose and the toxin protoanemonin, a lactone. The ability of protoanemonin to blister skin and mucose membranes was used medicinally, but also by medieval beggars to mimic skin burns and remove leprosy scars.
Ficaria was formally recognised as a separate genus in the mid-eighteenth century on the basis of its variable number of petals surrounded by three sepals. However, for much of the twentieth century, the genus was subsumed into the much larger genus, Ranunculus. By the end of the century, phylogenetic evidence, derived from DNA-sequence data, showed Ficaria and Ranunculus were separate genera.
The variable number of floral parts across the species' European range led to extensive academic debates about the existence of local genetic types and their identification in the early 1900s. Researchers found geographic variation in part numbers but also seasonal differences; late-flowering plants have fewer flower parts than early-flowering plants. This research was an early example of statistical techniques being applied to taxonomic discussions. Furthermore, it highlighted the importance of experimental design if environmental effects are to be eliminated when studying natural variation.
Naturally there are two sorts of lesser celandine that can only be distinguished based on chromosome number: diploids with two sets of chromosome and tetraploids with four sets of chromosome. When the two sorts occur together at the same location, triploid plants with three chromosome sets can be found. Diploid plants reproduce sexually via seed but tetraploids and triploids reproduce vegetatively by bulbils at the bases of the leaves.
Parkin J 1928. The glossy petal of Ranunculus. Annals of Botany 42: 739-755.
Pearson K et al. 1903. Cooperative investigation on plants. 2. Variation and correlation in Lesser Celandine from divers localities. Biometrika 2: 145-164.
Taylor K and Markham B 1978. Biological flora of the British Isles: 24. Ranunculus ficaria L. (Ficaria verna Huds.; F. ranunculoides Moench). Journal of Ecology 66: 1011-1031.