| Author | (L.) Nieuwland | |
| Distribution | Throughout the state, occurring in all 100 counties.
This is a very widespread species across most of North America.
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| Abundance | Often very common across the state, perhaps less so in the Mountains, but still common there. | |
| Habitat | This species and T. biflora have very similar habitats and often grow together. Both grow in grassy places -- roadsides, weedy fields, meadows, vacant lots, and other sunny open places. It can grow into open woods. | |
| Phenology | Blooms from April through June, and fruits shortly after flowering. | |
| Identification | Both Triodanis species are quite slender and erect, with mainly unbranched stems, but only reaching about 10-12 inches tall. Both have numerous alternate leaves, with flowers in leaf axils in the top part of the stem. They differ in several ways. This species has rotund leaves, about 1/2-inch long and wide, that clearly clasp the stem, whereas T. biflora has rounded to ovate leaves, but are sessile and not clasping the stem. Flowers in T. perfoliata often grow along much of the stem, whereas the other species has flowers only at the top of the stem, usually just one flower in bloom at a time near the tip. The pores in the capsule of this species are well below the apex of the capsule, whereas in the other species they are near the apex. Normally, the flower(s) of T. biflora is lavender to pale blue and not as rich violet as those found in T. perfoliata. Most biologists have little or no trouble in separating these two just by leaf shape, but flower location on the stem is also helpful. This is one of the most common native "weeds" in the state, and the often rich violet of the flowers is quite striking. | |
| Taxonomic Comments | This has always been a good species, but many references, but not RAB (1968) or Weakley (2018), have included T. biflora within it, as a separate variety, and that forced T. perfoliata to be listed as the nominate variety -- T. perfoliata var. perfoliata. Note that members of this genus were long included in the genus Specularia for most of the last century.
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| Other Common Name(s) | None. Many references call this as simply "Venus's-looking-glass", but that should be reserved for the group name, or the species if both were lumped into one. | |
| State Rank | S5 | |
| Global Rank | G5 | |
| State Status | | |
| US Status | | |
| USACE-agcp | FACU link |
| USACE-emp | FAC link |
