By Patsy Cotterill
The genus Ranunculus – the buttercups, spearworts and water crowfoots
This genus in the crowfoot family (Ranunculaceae) contains about 700 species distributed world-wide in temperate and montane regions. Its members are easy to recognize because the flowers have a similar simple structure, and most are yellow, with a lesser number of species having white flowers. Even the leaves have similarities of design, often with simple, round basal leaves with three-part divisions and deeply divided stem leaves, all with palmate venation.
It is thought the genus originated in northern Eurasia about 56 million years ago or later, and spread widely across the globe (except for the tropics), differentiating into different species. Most species inhabit cool, moist environments (including some truly aquatic ones), which probably explains the Latin name of the genus (Ranunculus means “little frog”).
There are some 300 species of Ranunculus in North America of which Alberta’s share is 24. Of these, seven occur in alpine or montane habitats and one is most often located in mountainous habitats. In these articles (two more articles will appear in subsequent newsletters) I will cover only our local Edmonton-area species, not the mountain ones. Several of these latter species are also quite rare. For those who frequent the mountains I will merely say that Eschscholtz’s buttercup (Ranunculus eschscholtzii) seems by far the commonest species in Alberta.
In our area we have 11 species, including two which are aquatic, the water crowfoots, and the others variously denizens of riparian muddy shores, natural grassland, disturbed open areas or moist, shady, often woodland habitats.
I will describe or refer to another two species that were once in the genus Ranunculus but have now been moved into other genera: Halerpestes cymbalaria (formerly Ranunculus cymbalaria) and Coptidium lapponicum (formerly Ranunculus lapponicus).
The Ranunculi are herbaceous plants; most species are perennial, but some are biennial or short-lived. The flowers are radially symmetrical, with five sepals that may become reflexed, and five yellow, or much less commonly white, petals. A ring of numerous, spirally arranged stamens lies at the base of a slightly cone-shaped receptacle to which are attached the stalkless pistils (usually referred to as carpels). Each of the numerous ovaries will form a single fruit (the achene) from a single ovule, the remains of the style often persisting as a beak.
A characteristic, especially of yellow buttercups, is that the petals are glossy and reflect light. This is thought to be adaptive in attracting pollinators and also in regulating the temperature of the reproductive parts of the flower. (As kids in Britain, where once the hayfields were full of buttercups and daisies, we used to play a game, holding a buttercup flower under each other’s chins. If the chin reflected yellow, that person was supposed to like butter!) Also characteristically, the petals have a nectary gland at their base, which may or may not be covered by a scale.
In this first article I will cover locally common species of moist, shady habitats.
Buttercups of moist, often shaded, habitats.
Ranunculus abortivus goes by several common names, including small-flowered, little-leaf, or kidney-leaved buttercup. Of these the first is probably the most fitting as this plant has the smallest flowers of all our local buttercups. The petals are not longer than 3.5 mm, and are shorter than the sepals which are 2.5-4 mm long.
It is an erect biennial or short-lived perennial 10-60 cm in height, which means that its populations vary. A characteristic feature is that its basal and stem leaves are different: the basal ones are round-ovate or kidney-shaped, with only shallow indentations (crenate) and on long stalks, the stem leaves, lacking stalks or with short stalks, are deeply divided into three narrow segments. The tiny achenes (1.5 mm) are smooth, with minute, curved beaks and together form a round or somewhat ovoid fruiting head. Small-flowered buttercup is commonly found in the moister areas of trails through woods. A single plant may escape notice, but where individuals are numerous or a small cluster occurs, it will attract your attention when it blooms at the end of May into June.
The other two local species that occur in woods, as well as in riparian areas, have basal and stem leaves similar although the stem leaves are often smaller and on shorter stalks. Macoun’s buttercup (Ranunculus macounii) and bristly or Pennsylvania buttercup (Ranunculus pensylvanicus) are quite similar to each other. They are both annual or perennial in growth habit, 30-70 cm tall, and hairy. Both have leaves that are divided into three leaflets which are further 2-3-divided into lobed and toothed segments. Macoun’s buttercup, however, tends to be a more prostrate or spreading plant, with sprawling stems that root at the nodes, whereas bristly buttercup is more erect and does not root at the nodes.
The two can best be separated on floral characters: R. macounii has petals 4-6 mm long, which are slightly longer than the sepals, whereas in R. pensylvanicus they are only 2-4 mm long, half as long as the sepals. The fruiting heads provide the most obvious distinction; in Macoun’s the heads of achenes are round or ovoid; in bristly buttercup they are cylindric-oblong. Both flower in early to mid-summer. Of the two, Macoun’s buttercup appears to be the more common and widespread, and bristly buttercup has a more northern distribution.
Have fun distinguishing the two! Both should be suitable candidates for gardeners who have some space around shady ponds, and should grow readily from seed.
Lapland buttercup (Coptidium lapponicum, formerly Ranunculus lapponicus) has as its name suggests a northern distribution and in my experience is rare in the Edmonton area. It is a species of mossy and peaty forests. I have seen it a few times in Wagner Natural Area but never in flower. The stalked basal leaves are kidney-shaped and divided into three wedge-shaped segments that are shallowly lobed. Unlike the buttercups, it has three sepals and 5-9 yellow or whitish, oblong petals. The achenes have long beaks that are curved and hooked.
If you come across this plant it would definitely be worth entering the record into iNaturalist (see Susan Neuman’s article in this newsletter).
References:
En.wikipedia.org(wiki)/Ranunculus
Flora of North America. Volume 3. Ranunculus.
Kershaw, Linda and Lorna Allen. 2020. Vascular Flora of Alberta: An Illustrated Guide. Self-published. Kindle Direct Publishing.
Moss, E. H. 1983. Flora of Alberta. 2d ed. Edited by J. G. Packer. Toronto, U of Toronto Press.
