KYBBY ID Tips: Common Small-flowered Buttercups

(Cross-posted from the KNPS Wildflower Week BotanyBlitz journal)

Today I thought we'd take a look at two common, native, small-flowered Buttercups, Ranunculus abortivus (Small-flowered or Kidney-leaf Buttercup) and Ranunculus micranthus (Rock Buttercup). In overall aspect, these two are strikingly similar:

• basal leaves on long petioles that vary from basically round to kidney-shaped to tri-lobed
• stem leaves that are deeply 3-lobed with lanceolate to oblong lobes
• dinky flowers
• not particularly restricted to any particular habitat, and can be found in a variety of dry to mesic wooded sites, fields, riparian areas, roadsides, etc.

Looking at them side by side, you can see how it's kind of a "Patty Duke Show" situation, but with buttercups:

(Left: R. abortivus by @easter22; right: R. micranthus by @sarcasticdungbeetle)

(Left: Basal rosette of R. abortivus by @sam727, right: Basal rosette of R. micranthus by @tanyuu)

Even so, you might be able to visually detect a key difference from the above photos: the foliage and stems of Ranunculus micranthus appears more grayish-green due to the presence of long, soft hairs on the stem and petioles, and the light pubescence on the leaves. Ranunculus abortivus tends to be darker or deeper green, because its stems, petioles, and foliage are all glabrous (hairless). This is probably the easiest ways to tell the two apart vegetatively; here are some closeups:

(Left: glabrous stem of R. abortivus by @emily7; right: softly hairy stem of R. micranthus by @vvoelker)

As you become more familiar with these two, you'll notice a few more differences:

• The bases of basal leaves are more truncate to cuneate for R. micranthus, compared to kidney-shaped to cordate for R. abortivus
• On average, R. abortivus tends to be a bit more robust in stature, often with with stouter stems
• Although it is possible for them to co-occur in the same habitat, R. micranthus is slightly more conservative and skews toward somewhat drier habitats

For further reading and additional comparison notes, the website Missouri Plants has great photos and descriptions of both R. abortivus and R. micranthus!

Note: these are not the only small-flowered Buttercup species in Kentucky, but they are two of the most common and widespread lookalikes. A few other small-flowered Buttercups to be aware of include:

• Ranunculus recurvatus - Also common and widespread, but with larger stem leaves and generally less likely to be mistaken for abortivus or micranthus (distribution in KY)
• Ranunculus allegheniensis - Restricted to the southeastern Appalachian Plateau counties, this species may resemble R. abortivus in overall aspect and glabrous stems, but with hairy sepals instead of hairless (distribution in KY)
• Ranunculus harveyi - Most similar to R. micranthus, but with noticeably slightly larger petals. This species is only known from Cumberland and Clinton Counties in Ky (distribution in KY)
• Ranunculus sceleratus - tends to be a wetland or wetland-adjacent species (distribution in KY)
• Uncommon to rare native wetland Buttercups - Ranunculus ambigens, Ranunculus laxicaulis, Ranunculus pusillus
• Non-native and weedy - Ranunculus parviflorus

Posted on March 21, 2022 03:07 PM by vvoelker