Since violets (Viola species) hybridize so readily, they can be tricky to identify. Individual plants sometimes show characteristics intermediate between two species. Take a look at the USDA PLANTS Database page for Viola and you’ll see what I mean: of the 129 species shown there, 43 are hybrids. (Presumably these are naturally occurring hybrids, not cultivated varieties.)
Yellow violets are easier, because there are only a few species, and only three of those are found in Maryland. Right now, one of them is blooming in the Potomac gorge area: smooth yellow violet (Viola pubescens var. scabriuscula, formerly known as Viola pensylvanica). There’s a second variety of the same species that’s commonly called downy yellow violet (V. pubescens var. pubescens).
I started writing this post almost a year ago, then realized I didn’t have any good photos for it, so set it aside until now. Over the last few days I’ve examined a few dozen yellow violets, and they’ve all been the smooth variety. I hoped to have photos of both for this post, but if I wait too long I’ll have to set it aside again, so here goes.
The two varieties bloom at about the same time (April) and grow in the same habitat (moist deciduous woodlands). The main difference between the two is hinted at in the name: in botany, pubescent means covered in short hair, while scabriuscula means slightly rough.
Although this one is smooth yellow violet, you can see some pubescence on the leaf base and adjoining stem on the lower right leaf. Smooth yellow violet can have a slight pubescence but is mostly glabrous (smooth), which you can see on the rest of this plant.
Another identifying characteristic is the shape of the stipules. Those of downy yellow violet are broadly oval, with a blunt tip, while those of smooth yellow violet are narrowly oval, with a pointed tip, as shown here. (A stipule is a small, leaf-like bit of tissue found where the petiole meets the main stem; there’s one in the very center of this photo.)
Finally, look at the whole plant: downy yellow has a single flowering stem, with one basal leaf or none, while smooth yellow has two or more flowering stems and one to three basal leaves.* The plant pictured here appears to have three basal leaves (at one o’clock, six o’clock, and eleven o’clock), one flowering stem with a blossom and a bud (seven o’clock), and a second flowering stem still developing (twelve o-clock).
I’ll keep looking at yellow violets this spring, and if I find any of the the downy variety I’ll write a follow-up post.
*descriptions from the Flora Novae Angliae by way of the New England Wildflower Society’s gobotany website (which every botanerd should bookmark):
1a. Stems solitary, with 0 or 1 basal leaves; leaf blades densely pubescent; stipules broad-ovate, with an obtuse apex … 21a. V. pubescens var. pubescens
1b. Stems 2 or more from the apex of the rhizome, with 1–3 basal leaves; leaf blades glabrous or sparsely pubescent; stipules lanceolate to narrow-ovate, with an acute apex [Fig. 935] … 21b. V. pubescens var. scabriuscula Torr. & Gray
Violets in California are not much to look at. As far as I know, there is only one yellow one here, at it is sometimes white or creamy white. There is a spectacular yellow violet in western Oregon!