By Patsy Cotterill
Ranunculi: Part 2. The Aquatic and Riparian Species
In a previous article (https://www.enps.ca/post/plant-profile-buttercups-part-1), we described the buttercup species (members of the Ranunculus family) found in the Edmonton area in moist, shady terrestrial habitats. This article will examine those species found in wetter conditions.
The water-crowfoots (two species in Alberta)
The water-crowfoots provide an interesting example of how complicated taxonomy can get with species that are circumpolar and wide-ranging. Names change and treatments differ, and looking at various sources can be confusing. According to Kershaw and Allen’s Vascular Flora of Alberta (VFAB), which follows the national vascular plant database Canadensys Vascan, there are two species of water-crowfoot in Alberta: Ranunculus trichophyllus (which is called Ranunculus aquatilis var. capillaceus in the 1983 edition of Flora of Alberta) with the common name of thread-leaved water-crowfoot, and R. longirostris (formerly R. circinatus var. subrigidus), with the common name of long-beaked water-crowfoot in VFAB. Canadensys Vascan considers R. circinatus, a Eurasian species, as present in B.C. and from Ontario eastwards, but absent from the Prairies. If it were to be found in Alberta, that would make three species.
Both species are submersed aquatics in ponds, lakes and creeks. Their floating leaves are finely divided into fine, thread-like segments which assume a circular or fan-shaped outline. The single white flowers are borne on long stalks from the leaf nodes along the slender stems and rise above the water surface. The petals, 4-9 mm long, are white with a yellow spot at the base. The tiny, crowded achenes form a small, rounded fruiting head (see second photo below).
Likely long-beaked water-crowfoot (Ranunculus longirostris) in Strawberry Creek Natural Area, 2009-07-20. Photo: P. Cotterill.
Mounted specimen of Ranunculus longirostris, collected in Magrath, AB, 1991-07-24, showing fan-shaped leaves and lack of leaf stalks.
Mounted specimen of Ranunculus trichophyllus, thread-leaved water-crowfoot. Photo taken by P. Cotterill of a specimen collected in Leaf Rapids, Manitoba on 1978-06-14.
The character usually given for separating the two species is that R. longirostris has firmer leaves that do not collapse when taken out of the water, compared with the softer, collapsing leaves of R. trichophyllus. However, this is not a particularly useful feature if you don’t have both species for comparison. As the name suggests, in R. longirostris (the specific name is Latin for “long beak”), the achene beaks reach 0.5 mm in length (!) whereas they hardly exist at all in R. trichophyllus. Fruiting heads may be hard to examine – indeed, collecting the species at all may require hip waders or the plant being in shallow water or stranded on mud. Perhaps the best character is the length of the leaf stalk as it emerges from the stipular sheath at the base: it is longer than the stipule in R. trichophyllus, but barely exceeds the stipule in R. longirostris. This feature, along with the texture of the leaves, gives the plants a different look when they are mounted.
Long-beaked water-crowfoot is much the commoner of the two species, having a fairly wide distribution in Alberta and on the North American continent as a whole. Thread-leaved water-crowfoot is a more northern species and is circumpolar.
It is my impression that long-beaked water crowfoot has become less common in recent decades, perhaps due to the drying up of wetlands. This summer I was excited to see a floating white mass on Whitemud Creek in Whitemud Creek Park South, but on closer examination it turned out to be a population of floating marsh marigold (Caltha natans), another member of the buttercup family.
Terrestrial species that like muddy lake shores
Gmelin’s buttercup or yellow water crowfoot (Ranunculus gmelinii) is a yellow-flowered buttercup whose spreading stems float in water or root at the nodes on muddy shores, forming attractive patches. The leaves are circular in outline and divided into three segments which are further 1-3 divided or lobed; their edges are shallow-rounded-toothed (crenate). Floating or emersed leaves are usually smaller and somewhat thicker than the submersed ones. The flowers, borne on long stalks, may have more than five petals, are 3-7 mm long and form rounded heads of achenes about 3-8 mm long. The species is widely distributed across Canada and northern North America and can be readily found in the Edmonton area. It blooms from late May through the summer.
Submersed leaves and stems of yellow water crowfoot (Ranunculus gmelinii) with flowers above the water surface. Sandhills Trail, Elk Island National Park, 2015-05-30. Photo: P. Kyle.
Seaside crowfoot (Halerpestes cymbalaria, formerly Ranunculus cymbalaria) occupies similar habitats to Gmelin’s buttercup, occurring on the muddy shores of ponds and streams. It may become inundated when water levels rise, but it is essentially terrestrial. It creeps by means of stolons which root at the nodes. The leaves, however, are quite distinct from those of R. gmelinii. They are basal, on long stalks, spade-shaped in outline, undivided and usually heart-shaped at the base, with shallowly-toothed margins. The yellow petals are 3-5 mm long and the fruiting heads of the achenes are oblong-cylindrical. It is common throughout Alberta, although less so in the north, and is widely distributed in North America as a whole. The species blooms during the summer.
Seaside crowfoot (Halerpestes cymbalaria), Whitemud Creek, 2009-08-26. Photo: P. Cotterill.
Cursed crowfoot/buttercup (Ranunculus sceleratus), our third common riparian species, is circumpolar and wide-ranging, occurring in both North America and Eurasia. It comes in two varieties: var. multifidus, native to western North America and as far west as Ontario in Canada, and var. sceleratus, which has an eastern North American distribution and is considered non-native. The common name of var. multifidus is celery-leaved crowfoot and that of var. sceleratus is cursed crowfoot, the name also of the species as a whole.
The species is a tall (to 60 cm), erect annual or short-lived perennial growing on the muddy shores of ponds and ditches. It has stout, hollow, much branched stems bearing many flowers. The long-stalked, kidney-shaped leaves, both basal and along the stem, are built on the three-part plan, divided into three segments which are again divided or lobed (in var. multifidus), with crenate margins. The yellow petals are 2-4 mm long, shorter than the sepals, and the fruiting heads of achenes are ovoid or short-cylindric and smooth. It flowers throughout the summer and its abundance seems to depend on water levels and the amount of exposed mud.
In the variety sceleratus, the leaves are only once divided into three, and the achenes are cross-wrinkled. Var. multifidus is the common variety of Alberta, but it may be interesting to check the achenes for cross-wrinkling vs. smoothness to see if the non-native variety is spreading.
Care should be taken when handling this plant, however. Its common name of “cursed” refers to its comparatively high content of the toxic chemical protoanemonin which, when the plant is cut or bruised, can cause blisters on human skin.
Celery-leaved crowfoot (Ranunculus sceleratus var. multifidus) at Clifford E. Lee Nature Sanctuary, 2021-07-11. Photo: P. Cotterill.
Celery-leaved crowfoot (Ranunculus sceleratus var. multifidus) in the dugout at Bunchberry Meadows Conservation Area, 2023-06-06. Photo: P. Cotterill.
Part 3 of the Ranunculi series will appear in the next issue of WN.