The purpose of this page is to provide an identification aid for trout lilies (genus Erythronium) in North Carolina. This is a fun one! Misidentifications run rampant in this genus - guilty of it myself - due to a fairly recent split into two species that doesn't seem to have trickled down yet into popular field guides. It takes a closer look at certain plant features according to more recent botanical manuals to sort them out.

The two species in question are E. americanum (the "original" trout lily) and E. umbilicatum (dimpled trout lily), which was split out and described as a separate species in 1963. Both have yellow flowers and mottled leaves. It turns out that E. umbilicatum actually is the more common one in the state, but this fact is nearly impossible to discern from field guides targeting the lay person. Out of a dozen pictorial wildflower guides for NC or the surrounding area on my book shelf, more than half only list E. americanum and make no mention of E. umbilicatum. Three provide prominent treatment and a picture for E. americanum and do acknowledge that another species exists, but seemingly as an afterthought. Only one book gives E. umbilicatum the more in-depth discussion but happens to get the identification features mixed up, erroneously stating that this species has auricles on the tepals, which actually is a distinguishing characteristic of E. americanum. None of the books have pictures of both species showing distinguishing features. In conclusion, popular field guides are of no help in this matter and will lead to misidentifications of E. umbilicatum as E. americanum.

Even herbarium data has to be taken with a grain of salt as many old specimens identified as E. americanum may in fact represent records of E. umbilicatum. The curators of the range maps caution about this and tried to account for it by considering only recent records and those that have been reexamined and confirmed, but there may still be some errors and an underrepresentation of actual occurrences in the maps. Both BONAP and SERNEC data suggest that E. umbilicatum is the more wide-spread species in NC. E. umbilicatum is common in the mountains and southwestern Piedmont, while E. americanum occurs less frequently in the Piedmont and is rare in the mountains.

(Map data from BONAP, top, and Vascular Plants of North Carolina, bottom.)

The first clue to species identity in this case may be habitat type. E. americanum is described as a species of basic mesic forests and rich bottomlands, limited to very rich, high pH soils. This rules out most habitats in the mountains and Piedmont, which tend to have low pH acidic soils. E. umbilicatum is not as picky about soil pH and grows in a wide range of forest types, including those acidic soils typical for the Southern Appalachians.

The best way to identify to species level based on morphology when in bloom is to look for auricles ("ears") on the innermost tepals. Other characteristics like the color of the pollen or tepals are apparently not reliable diagnostic features due to their high variability. Only E. americanum has these auricles while E. umbilicatum does not. The picture below shows what to look for (highlighted by the circles in the enlarged picture).

(Image source: Wikimedia, public domain; see Flickr for another great picture showing the auricles)

However, the best stage to distinguish the two species is when they are fruiting. E. umbilicatum is named for its umbilicate capsule, meaning it has a dimple in the top resembling a belly button. The capsules of E. americanum have rounded or pointed tips instead. (For a side-by-side comparison, check out the capsule pictures on Carolina Nature). The stalk that is holding the capsule is weak and flops over, causing it to rest on the ground in E. umbilicatum, while it is able to stand upright and hold the capsule "arching gracefully like a swan" as I've seen it described in one account for E. americanum.

(Image source: Wikimedia, shared by user Doppelbrau with a CC BY-SA 4.0 license)

E. umbilicatum is further divided into subspecies based on the presence or absence of stolons.

Posted on November 13, 2019 02:02 PM by annkatrinrose